Transcript for:
Earthquake Fundamentals

hi everyone and welcome back to another lesson in your favorite class of the semester geology so this week we're going to be covering earthquakes and deoration so like faults and folds how the earthquake energy propagates through seismic waves you know it's going to be a lot of good times there's going to be a lot of good information that we should all be aware of you know because of where we live so I want you guys to you know pay a lot of attention and take good notes uh this lecture is going to be about 3 hours in length and then next week we'll come back to this topic briefly we're going to cover everything with earthquakes and this lecture and uh faults and folds except for some of the damages and Hazards we'll touch upon that briefly next week and next week we'll also cover um topographic maps so this week make sure that you uh you you know watch this lecture uh there's a homework assignment make sure you do that don't forget to post on the discussion board related to this assignment because that's how I'm keeping attendance as well as how I will be giving participation points for this week and then on top of that there will be a lab this week where we will be going over some you know earthquake stuff so when you watch go to the lab make sure you check out the video at you know the start of the canvas page it should be right near the top where I'll go over the lab it's a really great opportunity to you know actually get a little bit of practice you know and a little bit of um kind of more directed advice now as always I want to remind you that you can email me your Labs early if you have questions about them or if you want me to just look them over um but other than that let's get into it now most people intuitively know what an earthquake is you know it's when you're you know taking a a walk around town or you're you know maybe sitting uh at your local Starbucks and enjoying your delicious tasty beverage and the ground starts to shake you know oh earthquake but you know let's try to get a little bit more technical about that so you know the definition what you guys to think of when you're thinking of earthquakes is that it's going to be any Earth shaking like any ground shaking caused by the Rapid Release of energy now that's just making it a little bit more technical but let's make it um let's make it a little bit more applicable let's think of this in a different way so as an experiment let's go ahead and clap our hands when you clap your H hands you're making a noise but what you're really doing is you're rapidly moving your hands and at that moment of impact you are compressing the air between your hands now that compressed air is going to escape and it's going to leave that point of impact as a wave and it's going to be a wave of air particles that are being compressed and air particles that are expanding out like uh extending and it's going to be uh moving away from it in this like weird frequency of extension and contraction and it's going to travel you know through the medium of the rest of the air until eventually it hits your ear and the nerves in your ear are going to translate that you know frequency of oscillations of compression and contraction to as sound now we often imagine this or picture this as like you know these linear waves traveling through the air but in reality it's going to be leaving that point of impact as a sphere we call them spheroidal waves because the waves are coming out in all directions in a perfect sphere evenly now we know this because if you're standing in the middle of a crowded room and you slap or clap your hands you know everyone in the room is going to hear it you know that impact is going to create you know frequency vibrations that are going to travel in all directions and hit everyone's ear so earthquakes are kind of the same idea in the form that you have a rock that's you know like in the ground you know like deep underground you got Solid Rock and you get enough energy built up in the Rock and we're going to talk about that process later that eventually it cracks The Rock and the rock moves you know in a sense you can picture that movement as like that clapping and so it's not going to be you know compressing and releasing air in this context it's going to be compressing and extending Rock now it's going to granted you know maybe move a little bit more a little bit less than the sound but much like that sound wave it is going that uh wave of energy we call those seismic waves that wave of energy where it's compressing and uh and Contracting the rock as well as moving it in all sorts of different ways we're going to talk about later it's going to extend outward from the source in all directions and the process like the result of this is going to be an actual shaking or movement of the ground and so that that's what an earthquake is and so um I think this picture on the right here shows it pretty well you know where you apply some stress to the Rock and it would be like kind of having a stick and you're kind of bending it now that solid stick you know at first it's going to deform a little bit because you know it has some strength you know the the the stick itself has a certain amount of strength so you're applying a certain amount of pressure to it you know you're applying energy to that stick and it's why it's deforming but it's not enough energy to break but at some point if you keep you know applying more and more stress you know in a sense like these tectonic forces applying more pressure more stress over time you finally get to the point where you have enough energy that it actually breaks the stick or breaks the Rock at which point in time it's going to separate and as it separate you know that motion that vibration that's causes by that breaking and separating is going to be your earthquake now earthquakes are super common and when I say super common I mean we have more than a million detectable earthquakes every year and that's just the ones that could be uh detected by our equipment from a distance uh if you can could include like if you wanted to go with the technical definition I mean you would have countless quadrillions you know but uh but for the most part you know you're having like about a million detectable earthquakes every year uh but almost all of those earthquakes you're no one's ever going to feel because most of those earthquakes are shaking the Earth so little that even if it was happening right now you know you're just not sensitive enough to detect it now geologists have some pretty cool equipment and we can actually detect these extremely fine motions in the ground and we can use that to you know recreate um the conditions we can say oh wow there was an earthquake and could even detect where that earthquake came you know in processes we're going to talk about later and so you know most of them are just you know not noticeable we only really notice them when they're big enough to really you know actually cause us to move you know and it happens especially in places like California I mean just this year we've had like here in Fresno we've had earthquakes that were felt like this summer you know that's pretty cool so um and so in as that regard you know even like the notable ones are fairly common uh in fact you can go on the internet and go out like you know earthquake tracker you know and you can actually get a list of like all the earthquakes above you know like that threshold where you can start to feel it and you'll be surprised I mean sometimes there's like dozens or hundreds of them in a day you know um usually you might be looking at more like a few to a dozen you know just depends on the day um but like I said they're very very common now most earthquakes are the result of tectonic plate motion because you know by definition anything that's causing motion of the ground is technically causing an earthquake in theory if you were to jump up and down you're causing an earthquake but we don't really count those because those are too low energy they're just effectively unnoticeable you know when we're talking about earthquakes for this lecture we're really talking about the ones that are releasing huge amounts of energy and the more energy that's being released the more the ground shakes and the more we're likely to feel it and so it really takes you know tectonic motion you know like like the the motion of these tectonic plates to generate enough energy to really create these earthquakes now when you're dealing with Earth processes you're often dealing with values that are a bit absurd on a human scale now if you want go with like a really large earthquake like the earthquake that destroyed San Francisco back at the start of the 1900s and the first like what like the first minute or so of that earthquake it released enough energy to power the entirety of the US right now for a year and it was like actually less than a minute it was like uh I forget their exact calculation but it was like the first like 30 seconds or something like that and that was just the energy that was released that we you know detected and picked up so when you're dealing with Earth processes always keep in mind that sometimes you're dealing with scales that are you know not really human scale you can deal with like or energy at orders of magnitude way above human consumption you can deal with periods of time that are almost beyond our Reckoning it's one of the funnest things about geology is that you can deal with Concepts that are just so much bigger than us so the end result of course is that you know while almost all of these earthquakes are super small and effectively unnoticeable you know we have to be aware of them because some of them can be very large and some of them can be very destructive and even when they're not particularly destructive you know that Earth motion can create you know notable changes you know so for example you might have a railroad uh track that suddenly gets sh shifted you know 8 in and now you know you can no longer run a train on it because one side is 8 in farther to the right than the other side things like that so there could be a lot of different causes for earthquakes and we should explore some of this now this earthquake activity can be caused by anything really I mean like I said by definition jumping up and down can cause it it's just too little damage to be noticeable but there are a bunch of causes that can create significant enough changes um in motion to actually be detectable with our instruments and so I'm going to go through some of these pretty quickly so the most common one is going to be some sort of sudden motion or uh some sort of slip along a fault and we're going to go into faults later but a fault you can just imagine as like a crack in the ground like a break in the Rock along which there is motion so you might you know there might be a break that makes a newly formed crack or you might have a pre-existing crack that's going to uh do this uh generally speaking if you have a fault in the area earthquakes are more likely to um happen there that makes it the by far the most common thing and as an example of this you can just consider like a piece of paper I mean this is an experiment you can try right now at home like take a sheet of paper kind of like hold it in your hands flat you know where you have like gripping one end with one hand and the other with the other hand and kind of try to pull it apart a bit and you'll notice that you know you might make some slapping sounds but the paper's not really ripping and then you know take the paper and kind of put a little tear you know like maybe like a 2in tear in the center um along one of the edges up um between the two sides and and then do it again and you'll find that that paper rips pretty easily and it's going to rip along that rip because once you have that weakness that that break which is now a zone of weakness then the energy is going to be able to focalize there and you know tear the rest of the paper more easily so in this context FAL lip is going to be the most common cause of earthquakes now for the other ones you can have things like a sudden change in Mineral structure and we haven't really touched upon minerals yet you know that's going to be um a little bit later uh I believe it's going to be for the next unit but more or less uh when you have these tectonic motions and you're forcing a plate to go deep like a subjecting plate to go deep into the ground that change in temperature and that change in pressure can occasionally cause the chemistry of the RO to change like the minerals to form new crystals and by doing so it can actually change like the volume of those crystals and that can in turn create um Mo motion uh you can also have um magma like moving a magma in a volcano or a volcanic eruption itself and we're going to talk about volcanos more you know later on in the semester but you know magma is basically like lava it's just lava that's underground and before like it before a volcano over erupts you can even if it's not imminent you know sometimes that magma might have a sudden shift it might just move underground and that can create an earthquake and obviously if it hits the surface it's going to make a it's going to be pretty violent that can also shake the Earth um giant landsides can do that I mean landsides are super common like super common we're going to talk about that in a little bit later on in the semester but um there are cases like especially with like um you know the continental shelf like off the in the oceans things like that you can get these landsides that can be truly massive and that is so much movement of Earth materials that it can lead to another earthquake and of course you got things like meteorite impacts I mean that's just hitting the ground really hard or nuclear detonations which would be the similar process all of these things can create earthquakes but generally speaking whenever we're really talking about earthquakes for the rest of this lecture or any times you really hear earthquakes on the news almost always the earthquakes are referring to is going to be you know basically the release of that tectonic stress caused by fault slip or let me rephrase that the release of tectonic energy caused by that plate motion no matter how far away it is that's being released along a fault I guess that would be the more accurate way to say that now keep in mind also that um earthquakes don't have to only occur exactly at those play boundaries because those stresses that all this is causing can translate through the Rock and actually build up in other places they're more common in maybe like a few hundred miles on either side of like a major play boundary but you can actually have earthquakes almost anywhere on a plate uh because stresses can build up under different conditions it's just that when you get into the deep interior of a plate they're pretty rare if you go to like to you know my home state of Michigan or Illinois you're almost never going to find an earthquake there but it's possible in fact I once uh when I was some archaeology in Illinois there was an earthquake there once I mean this was so small was one of those ones that I didn't really sense it um some people I know did I I was walking so I didn't quite notice it uh but it was basically like a faal slip that no one was really aware of because it's been building up stresses so slowly that it probably took like tens of millions of years to build up enough to actually create that earthquake and it was so small was still even barely noticeable um and and of course you know there are like other processes that can determine earthquakes that I'm just not going to really go into because that's um a level of detail that's not needed for this class but you can have things like um crestal extension during um like following the subduction of a plate that created like de Basin en range there are other processes that can cause this when we talk about earthquakes there's going to be two terms which you're absolutely going to have to know and you're going to have to be able to distinguish between for the test so this are these are very important terms so you know going to put a little star here little star here and the first one's going to be your hypocenter which we often times call the focus focus is the more common term and you have the epicenter and so the focus of an earthquake is going to be where the earthquake started so for example if you were to take a sheet of paper you know and tear it in two then that tear as a whole is going to be like the earthquake SL fault Motion in a sense and that top of the page where it starts to tear that's going to be your focus in a sense because that's where the motion first started and so you can imagine the focus as you know where it starts in 3D you know bad handwriting and so the focus is almost always going to be deep underneath the ground the epicenter is going to be basically the spot of the land like on the surface of the land directly above it and so this picture up here let me change my color real quick this picture right here is a pretty good one because you can see where you have like the land here you know it kind of goes up like this and you had this fault surface so the fault surface is going to be this guy right there see me use a different color here that's going to be your fault surface right there which means that it's where the rock is broken where the slip is going to occur now when you have slip in these you know rock it's not going to be like in two Dimensions it's going to be a big chunk of rock moving relative to another big chunk of rock in some cases these big chunks of rocks can be really big and so you know that's why it's not really a fault line it's a fault plane which would be this whole area right here as worth STP caner curve and so as you can see this block up here of this block let me change my color again this block is going to be moving down it's like slipping down like that or in other words this side is going to be moving up like that let me make the color a little darker so nice dark Arrow nice dark Arrow here for you and so it's sliding down relative the top in this case is sliding down relative to the bottom and so where that earthquake first originates that's going to be the Earth or the focus of the earthquake you know right there and right here so that's where the fault first starts to move that's where the waves are going to first start to be released and then with in this context if you were to draw a line straight up then the spot on the surface directly above it is going to be your epicenter so for example if I were to create an earthquake you know with my magical geology Powers you know 20 ft down and then I were to stand like 20 ft down directly below my feet then that 20 ft down directly below my feet would be the focus and my feet would be standing on the epicenter now I said 20 ft but keep in mind when you're dealing with real earthquakes 20 mi would be more likely or two or 12 or so on and so forth now this picture over here on the bottom is going to be a map of epicenters uh along the uh Rockies so this is colorcoded where green is lower and brown is higher and the white is much higher you know and and so you can see how like you have all of these different um epicenters like earthquakes that have been occurring underneath those Mountain bases now the black lines you see there are basically the fault ples um it's how we call them fault traces it means that there's a fault either at the surface or underneath the ground that we've mapped and if you were looking straight down that's what it would be you know it's like the bird's eye view so if you notice most of those faults happen to be kind of along these highlights so you got a whole bunch here let me change my color again got a whole bunch here that color is not good either I'm going find a good color for you guys got a whole bunch here which is where most of them are happening but if you notice that's all along these black lines that are indicating that fault so it's kind of like what you see up here on the top picture you know where the B the top block is moving down relative but the bottom block is moving up relative so in a sense you have that uplift that's like that uplifting of mountains and when this happens over and over again over many many earthquakes you can move you know a block of land up super high I mean the Seer Nevada mountains comes to mind that's a slightly different case it was like Regional block uplift but the principle is still the same you know the whole ground has been uplifted from deep underneath we know this because the Sierra Nevada mountains are composed of granite and Grano diorites which are rocks which only form very deep beneath the ground which means that you know it had to have formed super deep and then has now been not only brought to the surface but then pushed up to be mountains you also notice how you got like these linear kind of features here these like linear mountains that's called the Basin and Range we're going to talk about that later but notice how you have the fs that are kind of going alongside that it's because the falter where that motion is and so it's lifting it up so it's it's actually really kind of cool so this bottom picture is representing the boundary between the Bas and range and the Colorado Plateau so that Uplands are going to be a portion of the Rocky Mountains but this principle is actually going to be true most anywhere where you have earthquakes or you have um Uplands so most of those other causes I mentioned of earthquakes you know will generally create really weak earthquakes you know things that might only be felt with instruments or things that you know might only be felt in a very you know localized area but you know when you're dealing with plate motion you know that's when you can start dealing with um you know really destructive really big earthquakes and so I wanted to kind of go into how these earthquakes occur and so you can imagine this as a series of steps where you have these rocks and and this plate you know these this mantle convection you know these the driving force behind plate tectonics it's trying to move the plate I mean it's trying to move the Rocks but the rocks are one solid piece I mean it's a solid rock I mean imagine taking like a a rock and trying to break it in your hands it's it's hard it's solid so you're going to have to like keep applying more and more stress to it more and more energy to it you know in the form of this like uh tectonic stress and it's still going to resist it and so the primary uh things that's keeping it from moving is going to be the friction and strength you know like in a sense like the chemistry of it the the the characteristics of the rock now just because you are applying you know this much energy to it doesn't mean and it's not breaking doesn't mean that the energy is just disappearing that that stress you know you can think of stress as energy that that stress is just going to be continuously built building up in the rock until such time that you have built up so much stress that you can overcome the strength of that rock you know you can overcome the friction that's holding all those pieces together and at that point it's going to break the Rock and it's going to slip and that stress that was being pented up there like being stored up gets released as like those seismic waves and so we call it the yield point um yield point when uh when you finally overcome it so I guess another way to say this is the yield point is going to be the amount of stress that is needed to be applied to the Rock in order to break it to overcome that friction to cause displacement to cause that motion and so once that rock is broken that energy is going to be released and it's going to be released as motion you know both the slippage you know that displacement as well as the shaking and it's going to keep slipping until you finally released enough energy that the remaining energy the remaining stress of the rock is no longer enough to overcome the friction at which point we start the process all over again and so we have something we call the elastic rebound model because um basically as the rocks are um as the rocks are being applied or having stress applied to this you'll often see some like large scale warping or deformation of the rock um and it will continue to deform Until It Breaks at which point the rocks will immediately slap back into the original shape so if you remember that picture a couple sides back uh with the stick you know as you're applying the stress to it you're bending it but so you know you're deforming it but once you know it breaks the both sides of those uh stick is going to become straight again so that's you know the basically how this earthquake goes now there isn't one single yield point you know that's something I want to really stress right now is that um you can have like this the type of the rock determines the yield point so you can have something like the San Andreas fault which you know is basically you know connecting along a lot of the West Coast and in fact um you know if San Francisco on one side and LA on the other side given enough time they will eventually become neighbors but you might notice that you get a lot more earthquakes in LA than you do in San Francisco and that's because in many places the Rocks over large areas around the LA area are weaker they they don't have as much strength behind them so it doesn't take as much stress to crack those rocks which means you're going to get a lot more slippage whereas the Rocks closer to San Francisco actually have a much higher strength so it can withhold that stress for you know a longer time before it breaks but when they do break they have a habit of breaking in a bigger way you know for example that giant earthquake that destroyed San Francisco in the early 1900s and the next Ultra major one that is probably going to happen in the next 30 Years uh statistically speaking there's about a 90% chance so you know just because like you have one fall kind of connecting the two representing that actual plate boundary you know the nature of the rock can differ from place to place and that can actually have an impact on the characteristics of the earthquakes themselves okay so this is going to be that picture to show it so imagine this as like time one time two time three and time four so let's begin with the stick pictures on the right because because I think these are going to demonstrate them better and so you have that stick and you're holding it and as you're applying pressure it's going to start to deform a little bit the stick is going to be strong enough that it's not going to snap yet you know it's not enough to break it but it is enough to deform it now if you continue to try to you know squeeze down on it eventually you will get to the point where the amount of stresser putting on that stick is going to be greater than the strength of the stick that's going to be the yield point point and so when you hit that yield Point you're going to snap the stick now notice how the in the picture you have it like bouncing around really fast like that vibration that vibration would be that shaking that we associate with an earthquake and then once that shaking stops or in other words the earthquake is done you know that stick is permanently displaced cuz you broke it but the shape of the stick goes back to its original shape in terms of like long and straight because of its elastic rebound and so we can see this with the land um you know we begin where you apply some land you know some basic amount of land Life's good you apply the stress and notice how you're getting that warping going on as you're trying to push it you know forward and backward in this case and then once it the yield point is reached it's going to slip so notice how the grounded sh is vibrating that's like that earthquake shaking we feel and the blocks are actually separating from each other and then once they uh stop shaking once the energy is released you now have them back in the original shape but they're going to be permanently displaced so like that would be like that false scarp like right here you know that that newly exposed area and in tectonics you know it stopped because the energy is released it's no longer strong enough the pressure inside the planet is going to kind of squeeze it so the rocks will start to reform which will again add to the uh add to all this and the stress will just continue to build up again until such time that it overcomes the yield point now you guys might have heard of aftershocks you know in fact I think we felt them uh this last week um and this happens when you have the earthquake occur and it releases a bunch of the energy and then it stops but that boundary between the two blocks are no longer smooth like it's it's kind of like two pieces of sandpaper kind of held together or they're not quite smooth it's like jaggedy and rough at which point you only need to add a little bit more stress to initiate a new slip because the yield point is very low at the moment and then of course it shakes and then you can either repeat the process you can have many aftershocks or you can done there is something also called for shocks which is where um you have like a little break and a little motion creating a little earthquake and then it gets preceded by not preceded it gets followed by a much bigger earthquake and then usually in that context you'd also have some aftershocks and we can sometimes use these four shocks as like an early warning to a coming main shock but the problem though is is we can never really be sure if what we're feeling is a fores shock or the main shock we only really know for sure if no other bigger earthquakes occur you know afterwards now there are some cool tools that we can use in this though um one of the things that I thought was really fun and fascinating is something called geophones which is basically like a microphone you stick in the rocks and the thinking there is is that as the yield point is starting to be reached but hasn't quite happened so like the deformation hitting its highest point but not quite enough to break it quite yet some of those Rock bits are actually going to start to break you're going to actually break some of these mineral crystals inside the rock uh and so it'll sound like kind of like the tinkling of glass if you heard it and so they put these geophones in the Rock and they listen uh well they have a computer listen I should say and when they start to hear uh a bunch of these crystals cracking then they realize that an earthquake is imminent that is one of the techniques we have to use as early warning for earthquakes but it's not the only one although I also want to point out right now that you can never truly predict an earthquake I mean you can sometimes get a little bit of a head start a little bit warning like with those geophones that giv you a pretty good idea one is imminent but it's possible that that early warning might only be 5 Seconds you know the best we can usually do is create statistical models meaning we look at the recurrence interval basically how often it occurs or how much time passes between earthquakes on average and we look at past examples we can use U we have special devices that can measure stresses no we can basically collect a lot of data and we can create a probability chart we can say it is this percentage likely to have happen within this amount of time for example a earthquake of six or 7.0 or greater hitting San Francisco in the next 30 Years is something like 90% meaning in the next 30 Years a fairly large earthquake at some point was a very large earthquake will hit San Francisco in the next 30 Years it doesn't mean it's guaranteed it means there's a 90% chance it'll happen uh and it could mean and it could also happen not in 30 years but at any point between right now and 30 years from now um there's also like a smaller percentage chance of it being even larger than that and if you guys are interested I could see if I can hunt down the article where they actually calculated all these numbers out just let me know the uh now probabilities are a good thing and it does help you plan um for example uh cities like San Francisco and Los Angeles are very well engineered particularly San Francisco we've engineered a lot of our buildings and bridges and stuff with the idea that an big earthquake is going to happen let's try to minimize the damage it causes and the country of Japan which is the most seismically active country in the world is also the most engineered country in the world their buildings are exceptionally well built to withstand earthquakes the largest earthquakes are usually associated with convergent play boundaries and remember that those are the play boundaries that generate compressional forces and so these earthquakes are often associated with mountain building and faulting and when you're dealing with like an oceanic uh Continental uh convergent boundary you also get something called a mega thrust fault now I'm not going to go into this at this exact moment and a little bit we'll talk about the different types of faults and a thrust fault is just one of the types of faults but a mega thrust fault is a fault that like a thrust fault that is just Mega it's just really really big you know and I'm talking like country scale continent scale you know maybe state scale you know you get the idea it's not like a little local fall it's it's one that can be hundreds perhaps thousands of miles long well 8,000 miles long you know depending on which one and where it is and when you have that oceanic continental convergence creating this Mega thrust VA these are the ones that generally produce the most powerful earthquakes um and if these earthquakes can produce vertical motion of the ocean or the water column you know for example by triggering a landslide or thrusting a big chunk of land straight up underground or underwater this can create tsunamis and we'll talk about this a little bit later now I'm not saying that all the biggest earthquakes are caused by convergent plate boundaries I'm just saying most of them are the San Andre's fault is a transform boundary creating strik St faults and those can also produce really big earthquakes as well so this is a block diagram showing a convergent play boundary that's going to lead to a mega thrust Vault so I got a couple of things here that are you know be good to notice so you have you know the oceanic crust there notice how it's thinner than the continental crust and it is moving it's towards the continental crust so it's moving this way and the continental crust is moving that way but because it is denser it is subducting down it is being pushed underneath this part right here is called an accretionary prism and we're going to talk about that in a future lecture now you're going to have the generation of a mega thrust fault which would be like this thing right here you know it' be associated with that trench for example it's going to be very big scale it's going to be along that whole play boundary or large portions of it at least now I mentioned uh in a previous lecture that these convergent play boundaries are associated with reverse faults or thrust vaults thrust faults are a type of reverse Vault and so the mega thrust is going to be what I just pointed out where it's this gigantic scale you know imagine like Japan sized but you can have these smaller ones let me CH get a different color here you can have these smaller ones like here and here and these are going to be associated with that uplifting of the mountains you also have that partial melting I talked about which is going to come up and lead to the volcanism right here here which can happen independently or in addition to the you know rising of the mountains and also take note how this is drawn I got all these squiggly lines here all the squiggly lines is representing ductile deformation and we're going to talk about that tomorrow so the type of plate boundary can actually also influence the you know sizes of the earthquakes so in general convergent boundaries are going to create pretty big earthquakes you know we got kind of two cases of this you know the first you know what's the number one here is going to be um where you have oceanic plate subducting underneath continental plate uh we call it um you know the one in the Pacific we call that the circum Pacific Bell because it rings the whole Pacific Ocean uh and we also call it like the the non-technical name is the ring of fire not the Johnny cast song and that actually is where we get about 95% of the earthquakes in any given year and some of these earthquakes can be some of the largest earthquakes you know we have now you can also get earthquakes along like Continental to Continental collisions and the big Continental to Continental Collision place we have right now is going to be the Alpine Himalayan belt which is caused by India um Arabia and Africa kind of starting to run into Europe and uh Asia and those actually can also be pretty big um in some areas they're not too bad but in some areas they can be pretty bad now at the divergent boundaries especially at the ocean ridges you can get these weak earthquakes because of like the tension pulling the plates apart and transform fults like the San Andreas kind of create these weird scenarios where you got these like large earthquakes but they follow a like cyclical nature so uh it's and it's based upon like that example I gave of yield point you know where it's building up the stress and it breaks and it has a habit of creating these like really cyclical earthquakes so I've been talking about faults a lot so far and before I really get into seismic waves and that sort of thing I want to talk a bit about faults in more detail because it is really important that you not only understand what a fault is but that you're able to identify ify what type of fault it is when you see a picture identify the type of stress you know what kind of play boundary it might be associated with and that sort of thing and there's going to be a bunch of questions about that on the test like there's going to be a lot of pictures of faults and you're going to have to answer questions about them so this is really important to know and really important you take a lot of notes on this so a fault is going to be a planer break in blocks of crust that's basically a fancy wave saying that it's going to be a broken surface and that surface is going to be flat and so we often draw these faults in the form of like simple diagrams something like that kind of showcasing um like a 2d picture of it but keep in mind like the black diagram you see in the bottom left these things are all occurring in three dimensions it's not just a line it's it's like a sheet also before I go any further I want to point out notice how I drew the uh Arrow here and here you can also see it in the black diagram here and here so these are going to be half arrows and it's one of the just little things we do in geology is when we're showing motion along a fault we do these sort of half arrows to indicate the relative motion to each other now when you're dealing with a fault most faults are going to have a slope meaning they're rarely going to be a pure vertical wall they're almost always going to have you know some sort of angle to them and they're not so they're going to be something like that they're rarely going to be like that there are some particular certain strikes St faults but most faults are going to have some sort of slope to them now when you're dealing with two fault blocks you know the you know the rock block above the rock block above below you're going to have your hanging wall block which is going to be the block of rock above the fault and you're going to have the foot wall block which is going to be the block of rock below the fault it doesn't matter what direction they're moving in terms of what they are hanging wall is just going to be if it's above it foot wall is going to be below it and so this is a really really really important distinction to make because in order to identify a fault you're going to have to be able to identify the hanging wall in the foot wall and I can guarantee there will also be questions about trying to identify a foot wall or a hanging wall on the test so this is something that's really worth practicing and really worth studying on now the final point on this diagram is going to be the fault scarp and a fault scarp is basically the fault plane that is exposed after motion so the fall plane is going to be know me use a different color here real quick oh didn't switch over it's going to be this full surface right here you know the whole sheet of it but the scarp is going to be the part that's exposed to the air after the earthquake after the motion so FAL scarps are really important like if you see a cliff that Cliff is generally going to be a false scar I can't say always because there are other Cliff forming processes that we're simply not going to get into uh except for one which is called carting which we'll talk about much later on well actually we'll talk about next week but um for the for the most part uh when you have these exposed like Cliff type surfaces that's going to be a fa C that's not to say that every time you have a fault it's going to be this nice clean break because keep in mind that once exposed to air it's now subject to weathering so you know if you see like a hill you know that Hill has the potential of actually being a fault scarp you don't know unless you could actually look at the Rock underneath a simple way to consider this is to actually look look at an example using you know a method how they determine the names of foot wall and hanging wall in the first place so I'm going to first begin by drawing a block of land just can keep it simple and put a fault down in the center of it and so the top here is above the fault and the bottom is below the fault so the bottom is going to be your foot wall and your top is going to be your hanging wall that's a terrible looking H now you may not remember like oh wait which side is up you know or whatever or maybe just get a little confused so let's draw a new one and so you have your fault plane you don't know what's going on so what you're going to do is you're going to draw kind of like a little tunnel like a little circle or something and in the little circle you're going to draw a person and so the person is going to hang their Lantern on the hanging wall and their feet are going to be on the foot wall and that is literally how those terms came to be you know because the miners when they were cutting through a fault would always be you know hanging their lights from the roof and the roof is above the fault and so that's the hanging wall and of course foot wall feet right another thing to consider is that the uh the direction of the fault doesn't matter so in this case I just drew the fault in an opposite direction but if I were to go ahead and draw like my little thing here and my little guy you know caring a little Starbucks cup you know and he's hanging his Lantern then again his Lantern is on the hanging wall and his feet are on the foot wall so I really recommend as you're taking notes you actually draw this out you know you know draw like the little block with the guy hanging the thing you know I'm a really terrible artist so you get terrible stick figures but you know I'm a geologist not an artist but this is a really good way to remember and even like on um on the test you know like when you're taking the test and maybe have a a sheet of paper on hand so if you see a picture and you're not sure you can just quickly like sketch it out and then draw the lines as you need to before I go into the different types of faults I want to give you like a simple trick that I use to remember the different types of faults and so this is only going to apply to normal and reverse faults because strike clip faults don't really move up or down you know they don't really have that hanging wall motion but the first one is going to be fun and fun stands for foot wall up normal and what that means is if you have a scenario where you have your fault so you know draw your little guy if you want you know you got your foot wall and you got your hanging wall so if your foot wall is moving up relative to your hanging wall me try drawing it like this you know your foot wall is moving up relative to your hanging wall but hanging it's going to be a normal fault now this might look a little bit harder to identify but remember you can always draw your little guy in there hanging his Lantern and feet on the wall ground you know it always works so now that you know the trick for identifying a normal fault the other one is going to be her which stands for hanging wall up reverse now some people choose to go with FD as in foot wall down reverse you know whatever works best for you and so again you can do something like like this where you have your relative motions being like this because your hanging wall is moving up relative to your foot wall and again if you have a hard time identifying this just draw your little man so note that that area right there that's going to be your false scarp same with the previous picture but you may have noticed that you don't usually see an overhang like that in nature because like I said once it forms it's subject to weathering and so in reality it would actually probably create some sort of slope like that so you have to look at the context of the rocks to actually identify in nature but for this test you know I'll keep them pretty straightforward like I just drew them now that I've given you the primer with my bad handwriting and worse drawings let's go into some actual black diagrams so this is going to be a normal fault you know again you have your exposed false scarp you know from that motion the line here is a fault notice the blocks showing the relative motion so the hanging wall uh is actually moving down relative to the foot wall so foot wall up normal got your little guy here as like your test if you needed it and and so you're going to get uh normal faults as a result of tension you know basically um extension caused by the pulling apart or stretching of the land so this is going to be tension stress and it's going to be Divergent boundaries okay I'm going to attempt to kind of showcase how that works using some bad art so let's say we have let me get some color going let's say we have a block of land cool but then you're going to start to pull that block of land apart you know so it's going to be your virgin play boundary right so as you're pulling this block of land apart it's going to start to develop cracks you know probably something along the lines of that now we're not going to go into the exact nature of why the geometries went like that in this case but at first they're just going to be cracks something called joints we're going to talk about in a moment now as you go on you're going to have a scenario were you know they're going to be kind of separated like this and this inner part of the block right here is going to fall and so because you know you just have only so much space so it's going to fall apart and so in this context if I were to draw this bigger you know you'd see something like this know continuation of the faults so this is of course the purple land area just try this aha even better coloring and so your fault motion is going to be like that and like that like that and like that now notice how in that inside block I drew two arrows that looked something like this and you're thinking wait that seems contradictory one is going down into the right the other is going down into the left well that's because these are showing their motions relative to the other side of the fault and so this is going to be your normal fault the next type of fault is going to be the reverse fault and so the reverse fault occurs as I said when the hanging wall is moving up relative to the foot wall this is caused by compression or you know compressional stress which is a form of like squeezing or shortening and with the reverse fault you're going to have a pretty steep slope you know so notice the angle of the fault here it's 60° so for it to be a reverse fult you have to have a pretty steep Angle now this is again going to be associated with your convergent clay boundaries and results from compressional stress so notice how the arrows are showing the block squeezing together and the hanging wall is moving up relative to the foot wall now I mentioned how we' have thrust faults uh in an earlier slide and so a thrust fault is the exact same thing as a reverse Vault but it's going to have a shallower angle in this case it's drawn at 30° usually you're looking at around 30 give or take 10 for your thrust vaults and around 60 give or take 10 for your reverse vaults you know the exact same processes are at play in both it's just that if it's a shallow angle we call it a Thrust Vault that is the only different typically we see thrust faults associated with like Mega thrust faults like those like um actual direct plate interactions and we normally see the reverse faults as like the local scale deformation so I'm going to attempt again to show how this works by using my amazingly great I mean bad art so we begin with the block and you're going to squeeze those rocks together and as you're squeezing those rocks together you're going to develop a couple of faults kind of a similar to the no normal fault it's just that in this case you're squeezing it together so we can imagine like you have your this remember this going to be your foot wall hanging wall and foot wall so let's go ahead and draw one foot wall here and draw the other foot wall here um they should be theoretically even I just drew them badly so you got your foot walls here but because you're squeezing these things together then you're going to have to deal with your hanging wall which is going to be squeezed upward relative to that foot wall because as you're squeezing it together you know there's only one place for it to go and that's up you know it can't go down because you'd be pushing against the entirety of the planet it has to squeeze itself upward and so your hanging wall is going to be moving up relative to your foot wall and again note the fault scarps that are created now be keep in mind though that I drew this with you know uh let's use this color with like nothing here I mean in reality there's always more rock underneath to fill in you know but I wanted to demonstrate it like that to kind of showcase a little bit better the last type of fault is going to be the strike slip fault this would be faults like the uh San Andreas fault and it is literally just a case where one block is moving past another block now this is the case where the strikes of faults tend to be vertical you know like like I said that they usually almost always have a slope in strike step faults they can be vertical or more likely near vertical in the San Andreas San Andreas fault's case it is actually near vertical in some places and less so in others and when it's like not vertical it creates something called a transpressional fault which then leads to what's called a stepover complex which is just way more detailed than you or anyone in elementary or even high school really needs to worry about right now so in general and for the test you can just consider that strike slip faults are going to be vertical and they're just going to be moving you know past one another and so as a reminder this is going to be using shear stress and it's going to be from a transform plate boundary and so notice how like the motion is just going to be moving past each other relatively speaking now we can actually further specify strike slip faults into right lateral strike slip faults or left lateral strik slip faults depending on the relative motion so let us try another gray case of truly terrible art to Showcase this okay so I'm going to try another attempt at fostering greater understanding through bad art so let's begin by making a block diagram and I already am going to apologize for how bad this is going to be so something like that so you can tell from the relative uh locations that this guy is moving up like this and this guy is moving up like that right so this is going to be a strik slip fault and this is going to be specifically a right lateral strike slip fault I just said SS for strike slip now you may be thinking um well how do you know for sure it's a right lateral and the idea is you're going to be looking at the relative motion of the block across from the fault which means it actually doesn't matter which side of the fault you're on like if you know you're standing uh let's say right here from your perspective You' be seeing you know me standing right here you know moving that direction but if you go from you know my direction let's throw a little Starbucks in there so you know it's me then from my perspective if you kind of just rotate the screen a little bit you can it would actually look like you're moving to my right if I was facing you so from your perspective facing me I am moving to your right and from your perspect from my perspective facing you I'm moving to my or you're moving to my right so it doesn't matter which side of the fault you're on that would be a right lateral strik step fault let's try a different perspective so if I were to draw my block diagram and another block here wow Badly Drawn but okay you can tell that the relative motions are going to be like that right and so again if you drew you know yourself standing here this time you got yourself a Starbucks and now I have two you know from your perspective facing me I'm going to be moving to your left and from my perspective facing you you're going to be moving to my left so it doesn't matter which side of the fault we are on based upon the fault on the other or based upon the motion on the other side of the fault the other side of the fault is moving to the left which would make this a left lateral strike slip fault and again I'm just doing SS for strik slip so we've gone through the different types of faults which are basically that brittle deformation um whereas like um that's you know resulting in motion but there is another concept I want to talk about and that's going to be this idea of joints and a joint is not going to be a fault but it is going to be a break or in other words a fracture in the Rock along which there is no motion so basically it's like a crack in the Rock but the Rocks didn't really move they just got cracked so imagine you're driving your car and a rock gets kicked up from the car in front of you and it hits your window and you get like a bunch of spiderweb cracks in your you know windshield those spiderweb cracks would be like a joint it's a fracture but there was really no motion along it it just was a crack and we'll often see these joints in response to Regional upw warping and down warping of the land so for example if you're having like the continent getting squeezed because of let's say other continents running into it you might create some sort of like Boe effect over a huge swas of land or you can have a similar effect just on a very small and local scale but it's not enough to actually you know break the Rock and cause a bunch of motion it might be enough to still fracture some of those crystals and that could lead to joints now there are a whole bunch of different types of joints out there we're going to be covering some when we go into um you know a future uh lecture but in general a joint is simply a break in the Rock along which there is no motion now I talked about displacement earlier but I want to bring about it again you know kind of go back into some of those terms I already talked about and so displacement is going to be the amount of movement across a fault so when you have that earthquake the fault blocks are going to move you know that that there's going to be motion it's not just a shaking like what we notice you know during an earthquake of course is a shaking but at that actual fault you're going to have displacement you're going to have one block sliding you know either past the other above the the other or below the other depending on where you are in relation to the fault you know and what type of a fault it is and so we sometimes call displacement offset because that's what we're ultimately measuring is we're measuring the offset between the two markers um that's actually one of the ways we were able to determine you know the relative rate of motion on some of these faults because I mean these faults uh are only going to really move during an earthquake and only little bits and might only see one in historical record or maybe we've never even seen another one like let's look at something like the San Andreas fault the San Andreas fault we wanted to know what the average rate of motion is and actually if this was my go1 class I'd make you guys calculate this out but what we wanted to do because sure we see little bits of motion here and again with all the different earthquakes but the earthquakes are not steady across the whole of the fault you know it moves more in other places and we're only getting a limited snapshot so what we do is we try to find something identifiable um usually like a really really big rock that you know is not can be found on both sides of the fault and so what we'll do is we'll look at really big rocks that are on one side of the fault and really big rocks that look similar on the other side of the fault and then we'll actually chemically fingerprint it we'll actually take a sample from both of the Rocks throw it in a machine to determine its exact chemical composition and if they match we say that they were formed at the same time you know it's like a it's like a fingerprint and so the idea here is that with San Andreas you know you had this um you the San Andreas block here or fault here and you had a rock that happened to form on both sides of it and we could and then over time it'll be displaced so that you know you're going to have like at one point later on you're going to have one chunk of the rock here one chunk of the rock there you know because of the relative motions how I'm drawing them and so we can say wow these got a big rock on one side big rock on the other side you know we can fingerprint them we know they're the same and so we measure how far apart they are and that's how much displacement there has been and then we can actually date the rock using methods we're going to talk about in week five and we could say Well it has moved this much much in this amount of time here is the average rate of displacement and so one of the things when they started doing this fingerprinting thing is they discover that the rocks on the San Andrea's vault have now moved hundreds of miles already you know because the displacement on a fault is going to be cumulative over time like meaning like let's say you know you have an earthquake and it pushes one rock you know to the left an inch well it's never going to go back the next earthquake it might only push it another inch but now you have a cumulative 2 in of displacement and like I said with the San Andreas fall cases it has now translated inch by inch into hundreds of miles all right quick pop quiz what is going to be the name of this feature that I am circling now so even though I can't technically physically hear you know your answers you know you guys are all such great students I sure I'm sure you already know that that is going to be a fult scarp you know that's going to be that that trace of the fault caused by the displacement of the land you know at the surface so in a sense you can imagine that you know this block of land right here was pushed up uh or conversely this block of land was pushed down and I mean when you're dealing with uh fall motion it's always about being relative so one could be pushed up the other could be pushed down or in reality it's probably a little of both and so uh this kind of goes into the thoughts of like the different types of thoughts you might have you know we talked about like you know the normal verse and whatnot but beyond that you know you could classify them as active or inactive and so an active fault is going to be a fault where you have ongoing stresses that are producing motion meaning that there is still shifting of the earth going on there and keep in mind that we could be dealing with like huge time scales you know like let's say the last time it shifted was a thousand years ago in geology that's just the blink of an eye an inactive fault is going to be where you know there was a break there and there was Motion in the past but you know the proximal causes of those stresses have went away and so there's not going to be really any more motion along those faults you know so for example um when you know North America collided with Europe you know to create Pangia you know that put a bunch of compressional stresses which made a bunch of um reverse faults you know over along the Eastern seabo you know created things like the Appalachian Mountains and that was cool but you know we're no longer running into Europe so those Faults Are uh effectively inactive right now they're not really moving at all and so it's also important to realize that not all faults are going to reach the surface you know we call we call them blame faults you know when there that break is only you know deep underground you know when they're basically invisible now there are various reasons that um you know a fault might become a blindfold you know the most common type of which is simply just the nature of the surface meaning you have a little bit of you have a break in the Deep Rock and you have some shifting and in a sense that break does go all the way to the surface but because the surface has like a deep layer of sediment like you know you might have like a few thousand feet of just loose sediment that that loose siment just sort of shifts a little bit and and it does it you know it it's sort of like you know you're like trying to break a box of sand you know like trying to break the sand in the in a sand box the Sand's just going to shift you know no biggie no harm no foul uh in other cases you know you might have actually had um the fall actually reach all the way to the surface uh in the past but then you had so much deposition of sediment and stuff that it's now so deeply buried you just don't see it you know either or it's possible and and both happen quiz time what kind of a fault is this before you move on to the next slide I want you to you know pause this you know and either if you you know print out a copy of the Powerpoints that's cool or um or sketch this out if you want and try to identify where the fault is uh try to identify like the relative motion meaning is it being pushed together or is it being pulled apart and identify the relative motion of the hanging wall and the foot wall and of course identify the hanging on foot wall so I'm going to just take a couple of seconds so you have a chance to pause [Music] this yeah my singing is about as bad as my drawing sorry sorry I just geology real good okay let's move on to the answer so this is going to be a normal fault because if you notice you have the motion going um to the right and left like it's pulling itself apart now we know this because let me uh go ahead and add some color to this you have the fault planes that I drew on here already and you can see the relative motions you know you can tell how this part is higher than this part and this part you know etc etc um now this is going to be your oh let me say foot wall hanging wall but here's where it gets weird this is going to be your hanging wall as well and that's going to be let me put this in red this is going to be a foot wall down here so that Center slice is both a hanging wall and a foot wall and if you look at the arrows it looks like it's moving both up and down right and that's because like I said those arrows are only representing the motion relative to the other side and the hanging W football is only representative of the other side so this is twof fa like so it's kind of a trick question don't worry there won't be trick questions like this on the test and it's representing like like I said uh a divergent boundary it's pulling itself apart so you can imagine that like that block is starting to slip in because it has more space than it knows what to do with I really recommend maybe even Googling fault and studying this because questions like that is going to be coming on the test I mean like I said this was a tw- fa system which was a little tricky but the principle is still the same you should be able to have identified the fault planes the hanging wall the foot wall the relative motions the type of fault the stress involved which in this case is tension and the plate boundary you'd expect to find it in which would be a divergent plate boundary to repeat my earlier point you know stress when you're dealing with earthquakes you know it's going to be a situation where your stress builds up but it's going to take a while to build up because the rocks are strong you know they're resisting it with their strength/ friction until you hit the yield point which is that point the amount of energy needed to finally break the Rock and once it's broken slip is going to occur you're going to get a lot of Shak the energy is going to be replace replaced by or the energy is going to be released as seismic waves and you're going to have displacement sometimes called offset and then you're going to repeat the process once the emotion stops you know it's going to take time to build up enough to break it again so there's a lot of terminology I've been going through in this lecture and if you have not gone through and been taking notes as you've been watching it I highly recommend you actually go back and rewatch it and take notes because this is very important to understand the Lexicon also while we're at it before we move on to the next slide how many faults can you identify in this particular picture so let me to give you a second pause it if you like now I'm not going to say I'm going to draw them all but I'll draw a couple of them got one here that's kind of goes up we got here here here here here um well that kind of continues up like that you got one here it's very hard to tell but you have the incipient one right here you have the deoration starting um it kind of goes up like that like that that oh got that one there got one right here got one right here got one right here you know and to be honest I'm sure I could find a few more if I kept looking so again this is way more complicated um then you I'd expect you to ever do on the test you know this is a lot of crazy faults by the way this is like these are normal faults so again tension but do not really expect you guys to identify all of those that's a little nuts the reason I put this picture on here in the first place though is scale like a lot of the pictures I've shown you were either Continental scale you know with like the mega thrust vaults or just really big you know things like mountains and stuff I mean San Andreas fall is huge right but um Faults Are any break along which there's motion so you so there size inv variant you can actually have very small faults in fact I once was looking at a s Like a Rock under a microscope so I was at a magnification that would be equivalent to like looking at really large bacteria I mean bacteria would be very small in that image but about that scale and I actually saw on the crystal I actually saw some slippage in like um of of the actual crystals themselves and when when I was plotting them I realized that I was actually looking at a fault in this rock on the scale of maybe a thousandth of a foot you know so like like a third of a millimeter you know I mean these are very very small breaks now I have no idea what caused them but it was a pretty cool discovery so the other question is going to be is if you can have offset or displacement without causing an earthquake and this is a really interesting question because the answer is yes now everything I've talked about so far all this faulting is called brittle deformation let me go ahead and circle that for you which means brittle is like you know breakable deformation is of course change it's deforming something you know so faulting as the Rocks cracking and breaking but rocks can also undergo ductile deformation which would be like a plastic flow so imagine um like a fault would be like taking a spaghetti like a dry spaghetti noodle and snapping it into two and ductile deformation be like taking a block of Play-Doh and squeezing it in your hand it just sort of oozes like the um kind of like the asthenosphere now when you have ductile deformation it does not generate earthquake because remember the earthquake is that breaking of the rock to release the energy whereas ductile deformation is going to be just sort of an oozing and flowing of it so you don't really have the same case like you're releasing a lot of energy because the rock is holding on to it because of its strength and a fault and then it breaks and releases it suddenly but if the rock is able to just ooze then it doesn't really have time to build up any energy as that energy is being applied it is directly making it ooze and flow more and so there are uh different reasons why you can have this ductile deformation but usually it's because of pressure and heat now we talked about this in the context of context of the asthenosphere you know the asthenosphere it's under ultra high pressure ultra high heat so it's just going to flow it's not going to break but that doesn't really apply to you know the crust the crust is definitely the lithosphere by definition the crust is going to be brittle so how is it that we're able to have conditions that allow for it to be hot enough and under high enough pressure in order for it to just flow and the answer is tectonic forces you know so the heat is just going to be the fact that it's deep you're always going to have this occur deep like 15 to 20 km down um and so it's going to be hot simply because of that geothermal gradient you're 15 to 20 kilm down it's going to be hotter so that helps now it's still not going to be enough pressure at that dep it'll still want to just break in fact we can easily get faults that go quite a bit deeper than that at times but in some situations let's say at a com virgin boundary like where you have compression the squeezing of the two blocks can put enough side pressure that it can actually make it act as though it's under a lot higher pressure than it is because it is under very high pressure like the the asthenosphere is under ultra high pressure because you have like you know 50 miles of rock above you putting weight on you in a convergent boundary you have two plates pushing into each other which is providing a similar amount of stress so you can so it can occur at a much shallower dep but the pressure is still going to be the same and so whenever you see ductile deformation it is always always going to be at a convergent plate boundary or some other position or situation where you have a lot of compression and so that deformation it creates by the way is going to be called a fold f o d and that's what makes these like wavy like patterns and we're going to talk about that a little bit more closer to the end of the lecture so we're going to be going into you know a little bit more detail on the different types of seismic waves here uh I recommend maybe taking a moment and pausing this presentation just taking a small break you know I think it would be uh beneficial but when you come back we know we'll start talking about the seismic waves so there are going to be two groups of seismic waves you know uh which comprise four total different types of seismic waves and so the first type is going to be your body waves and your body waves are going to be your p waves and your S waves and we're going to talk about each of those you know in more detail shortly now we call them Body Waves because these are the waves that are able to travel through the whole planet you know um this is how you know if there's an major earthquake anywhere in the world or generally any earthquake anywhere in the world we know exactly where it's at with great accuracy because we have seismometers we have these devices that can listen for them like all over the planet uh in fact we there's a kind of a subbranch of geology that we call seismology and seismology is basically you know looking at you know seismic waves like the study of seismic waves and trying to use that information to figure out what's happening inside the Earth and and so uh earlier we talked uh in great detail about the various Earth layers uh including like you know like the relative like iron content and all that other stuff and this is all information we know because of seismology we've never been able to dig anywhere near that deep but by creating like you know little miniature artificial earthquakes and Labs we have been able to get a pretty good idea of how um these seismic waves behave under different types of rocks and pressure and temperatures and things like that and so when an earthquake happens we take this absolute like mountain of data from SE seiso graphs like these devices from all over the world uh and we're able to then you know piece together like how deep each of the layers are as well as like the material that makes it up um we have gotten like collaboration of some of those deep earth materials through like kimberl pipes and things like that we're not going to worry about that you know in this unit in the next uh we'll talk talked about kimberl pipes a little bit in the volcano unit but we were able to determine all this information and in fact we also know for example that the outer core is liquid and the inner core is solid because of these Body Waves as well like the travel time should not be able to distinguish between the two but S waves assure waves are not able to penetrate any liquid and so we were able to create these like kind of sheer w Shadow zones and we're able to use that to identify the boundary of the uh outer core and then we're able to look at you know the defraction of the seismic waves as they the p waves as they hit the inter core to determine the size of how big the interc core is as well as how much it's growing every year so those are Body Waves surface waves on the other hand are going to be these the same idea it's going to be these seismic waves but instead of penetrating deep into the Earth they're going to be traveling specifically along the surface and so when an earthquake occurs most of the damage that is going to occur in that earthquake is going to be caused by the surface waves because they have the much higher amplitude they don't have as much punching power in terms of pushing through the whole planet but you know when they're going along the surface there's they're what's causing the greatest amount of Earth motion you know near the surface so I'd like to go into the different types of waves in a little bit more detail so the first wave we're going to be talking about is going to be a p-wave and a p-wave is the first type of body wave and so the P stands for a primary wave and we call it the primary wave because it is the fastest so this is going to be the fastest of all the waves and this is going to be an important point to note that the p wve is the fastest wave and I'll go into why that's important a little bit later on now we also call it a compressional wave because it is propagating through the Earth in the form of a wave of compression and extension or dilation of the material now this is where it might get a little bit weird you know but how these waves are transmitting through the ground is occurring kind of like how sound does in the form that it's going to be a displacement an elastic displacement so we think of energy moving like electricity or light like it just sort of flows through things but this is not how it actually moves this is actually propagating the energy via the deformation of the rock or soil that happens to moving through or water or air or anything else for that matter and so we usually try to describe this in the form of a very complex partial gradient function and I used to like to throw that equation up on the screen and say this is what we're studying today and you know watch people's you know horrified looks when they see you know calculus 3 on the screen but we're not actually going to be dealing with that because what that is ultimately describing is the motion of the sediment in three dimension as the seismic wave passes so if you remember when we talked about seismic waves yesterday you know I was talking about this in the form of like an energy wave that's kind of compressing the air and it's kind of creating this pattern of like compression and extension as it reaches towards you and a PE wve is much like this you know so what it is is that energy is propagating through the ground and when the energy hits a piece of rock it is going to push the rock outward and so in so doing it's going to compress it but as the energy wave continues Beyond it it's going to compress the next area and the area behind it will elastically deform back to its original shape but in the process it's going to extend itself and so you're going to have a compressive Zone an extended Zone in a compression Zone and so it's in a sense kind of Imagine like an accordion you know where it's in your hands you guys know those old tiny instruments you know you're kind of squeezing it you know together and aart together and aart together together and apart you know so imagine it like your hands clapping you know together apart together apart together apart this is how these p waves are propagating it's this compression together and apart dilation or extension and so it's usually not going to be a high intensity wave meaning the amount of damage this causes is going to be minimal compared to the other waves but it can still cause damage in its own right so imagine you were standing on the ground and all of a sudden you know you had your feet you know shoulder width apart you know you got a nice balanced stance and then all of a sudden your feet are just pushed together because the ground got compressed and then suddenly it got pushed apart until you're doing practically the splits now admittedly in an earthquake that degree of compression and dilation is never going to happen you're never going to see that degree of squeezing but the principle is the same and so because it's just simply pushing the material forward and then kind of releasing it and having it extend or getting pulled apart a little bit this is why I can move the fastest and this is also why it can move through anything because kind of like those sound wavs can travel through air or sound can travel through water so to can these seismic waves travel through the ground the rock the liquid core the solid core it doesn't matter it can travel through anything so for trying to understand you know the exact shape of the earth you know and specifically the dimensions of the inner core the p waves are Paramount they're super important I think uh the picture on the bottom showcases this pretty well and so you got a SC like let's say a slinky and you attach a slinky you know to a wall so it's you know nice and firmly attached and so that top picture you know this guy right here it's kind of indicating like it's kind of default State and what the picture is trying to show is like you know a pumping motion where the hand is pushing it in and then pulling it out and pushing it in so as it pushes it in it's going to compress the slinky in the immediate because your that energy is going to push it forward it's going to compress and then as that kind of forward motion propagates it is going to slide that compress forward Meanwhile your hand is pulling it back and so it's going to extend it so you notice how it's a little bit more extended over here and it's compressed here and if you complete this process you'll notice how you have like compression extension and here they have it back at its ground state but that would again be another compression if you continueed this motion and you can just keep doing this as long as you're kind of pumping your hand forward and backwards forward and backwards and so that's one of the things to consider is what the ground motion is doing is it's basically kind of compressing out from you and then being pulled towards you and then compressing out from you and then being told you so it's like compressing dilating compressing dilating and even though it's doing this according motion that action of according motion that compression extension wave it's always going to be propagating forward and that is something to always keep in mind we're going to be talking about the motions of all of these different types of waves but no matter what the motion of these waves are doing that motion is always moving forward so you can have that like compressed Zone moving forward followed by that extension Zone which you know was caused by moving backwards but during the next compression the extended zone is going to be traveling forward and then you're going to have a new compression Zone behind it which will also be traveling forward so on and so forth so this picture on the right kind of showcases this with a block diagram so you can see that you know in the undisturbed rock you know you can divide it up into these like perfect cubes and so you can have like these darker zones which are going to be where it's compressed you know you're squeezing those blacks closer together so like right here actually it's more like that and then you have your extended zones where they're kind of a little bit more spread apart like that and so you got your compression extension compression extension and so it's going to be moving forward that's going to be the direction of wave propagation but the vibration of the ground like that motion of the individual particles is going to be moving backwards and forward as it is being compressed and extended compressed and extended and so you know it's kind of a weird motion sense but um it's going to create like I said this according to motion traveling through the ground and it's going to be moving really really fast it is definitely the fastest S waves are going to be the second type of body wave and this is going to be the second fastest of the Waves so it's slower than the p waves but it's going to be faster than all of the surface waves and so this is going to be a different type of motion where the ground is going to be kind of going up and down in a wave like fashion and so I think this picture right here on the left shows it quite well so imagine and this is this is actually an experiment you can do at home you know take like a big piece of yarn or jump rope or something piece of rope and firmly attach one end to something solid that's not going to move you know like like a hook or a wall or something and then you'll pull the string taut and then as it's pulled taut just kind of whip your wrist so like you know you're quickly pushing it up and down and you'll see that that up and down motion is going to create like this little up and down wavelength structure and as you're watching it it will actually propagate forward so again you know the vibration is going to be up and down it's going to be the the sediment itself is going to be moving up and down but the energ that is moving it up and down is going to be propagating forward kind of like the bottom string it's just going to travel along until eventually it dies off now again s-waves have the ability to travel throughout the whole planet it does lose energy as it travel because there's still a frictional effect I mean you are deforming the you know rock so there is a frictional effect and the size of those waves will get smaller you know the farther away you are from Earth but when you're dealing with earthquakes especially like big earthquakes there's enough energy behind them that they can make it through the whole planet but with s waves it's going to be a little bit different because it can only travel through solid objects the second and s-wave actually hits a liquid or a gas it will immediately stop and all the energy is just instantly dissipated into the environment harmlessly and the reason for that is because of something in physics called sheer strength and that's because liquids and gases have no sheer strength I'm going write this out put the H down there that's going to be a r you know no sheer strength um and that's why we call it you know a sheer wave or you know we call it secondary wave because it's you know the second fastest or we call it a sheer wave because it's basically utilizing sheer stress and so solid objects have a sheer strength and because of that it can propagate but when you hit a liquid since it has no sheer strength then there's nothing for that energy to propagate through and thus it simply dissipates harmlessly into the environment um in terms of raw physics you will see a slight increase in the ambient temperature but a you know a negligible increase nothing to worry about and so this is going to be the second type of wave because the p-wave and the s-wave moves at different speeds it gives us a unique opportunity to find a way to triangulate the source or in other words the focus like where the earthquake starts and this is really cool and I want to mention it here since we just talked about the Body Waves but I'm going to go into this in more detail after we finish the uh other types of earthquake waves and then we go into seismic graphs so L waves are going to be you know the first of the surface waves and the surface waves are a bit different they move way slower than both the p-wave and the s-wave although still incredibly quick by you know human standards I mean like and excessively exceedingly impossible to match quick you know like supersonic jet quii um and so these waves though they're slower uh they only move along the surface of the planet and as as I explained earlier they only move along the surface of the planet because the nature of these waves mean that they very quickly uh get weaker as you get deeper now even though that these waves are slow and even though they can only really travel along the surface uh they are still the most destructive because the amplitude of their motion is greater and so this is something we're going to talk a little bit about with seismic graphs in a moment but the amplitude of a seismic wave is a function of how much the ground is moving you know and so the uh surface waves make the ground move more so in a sense the most intense of the shaking is going to be caused by the surface waves and so often times the other ones that going to create the greatest amount of Destruction now this is also why you know the earthquakes are most destructive near their focus or near their eper Center I should say because you know that's where you're going to get those surface waves that are out their strongest and as they're traveling on the surface they're going to quickly lose energy so the farther away you go the weaker it gets like if Fresno had an 6.0 earthquake um underneath our city like we would really notice it we would see cracks in the walls we would have things toppling off shelves our TVs would you know fall off our you know stands and break you know you know that precious precious Frappuccino on your desk that you're um P your hand so you can take quick you know refreshing drinks as you're watching this wonderful lecture would just jump off the desk and spill on the floor and that really is just going to be the ultimate tragedy there um cuz it's intense I mean it's a lot of motion but the Central Valley it's going to be a relatively stable place um like Fresno like the Central Valley as a whole very few earthquakes actually start in the Central Valley or I should say very few earthquakes of notable size they have it occasionally but it's it's relatively few uh but that doesn't mean we can't feel earthquakes from farther away so that earthquake that would you know be shaking our house and you know possibly putting some cracks in the walls things like that it's unlikely our houses would fall down in a 6.0 earthquake because in California we have laws requiring buildings to be engineered to withstand Earth Quakes up to a certain size um so even though our house might not collapse it would probably take us a bunch of damage if it was right beneath our feet but you know you might get an earthquake that starts farther away like Lone Pine or Nevada or you know San Francisco or something and when that happens there you know you're going to see all that destruction over there but by the time it reaches us I mean we'll feel it we we'll feel a little bit of shaking but it'll just be enough to be like whoa we're in an earthquake that's kind of cool but it's not not going to really topple anything it's going to be too weak at that point and that's because those waves are going to quickly lose their energy yet the longer they travel I mean quickly being a relative term U but these surface waves they are crazy destructive and their their motions are going to be a little bit different than the p waves and the S waves so the first type of wave is going to be the l-wave and the l-wave is going to stand for a love wave a isn't that sweet and so I I'll be honest I'm actually not certain why they call it a love wave I just like it and so the s-wave it's similar to an s-wave because like the swave was a situation where like the ground was kind of bucking up and down kind of like a undulations up and down the L wve is similar but instead of going up and down it is moving left and right kind of like the writhing of a snake you know kind of going side to side as it's moving forward and that's a snake is really the best way to think of this you know how it's moving side to side and it's doing this in order to push itself forward and I believe that it's pretty well expressed here you know in this bottom picture you know where you have that like back and forth motion or left and right motion but the wave is always propagating forward now notice how the individual blocks is seeing maybe some minor deformation as a function of that motion but only in the form of you know partial shearing of the shape you know not much and that's actually something I want to express right now is that these earthquake waves these seismic waves are all elastic deformation meaning you can you know Shear it you know to make it a little bit up long to push it up and down or left and right you can stretch it you can compress it you can do all sorts of things to these blocks but because it's elastic deformation once that energy wave passes it simply goes back to its original shape it will always go back to its original shape The Only Exception would be um unconsolidated self- sediment can you know sometimes change their shape a little bit so for example let's say you know I guess here's a way to think about this you know let's say you have one of those little plastic Kitty pools and then you put like a layer of sand on the bottom and then you then over that layer of sand you put a layer of flour and then you put a layer of sand back over that flower and a layer of flour over the sand so you have these alternating layers of you know like brown sand and white flour you know got the and these are nice flat layers inside this Kitty pool and then you picked up the kitty pool and you started to shake it like you would in an earthquake it's reasonable to expect that those nice flat layers are not going to be nice and flat and even anymore they're going to be rippled and mixed and churned you know and so soft sediment would be the exception because they're not Consolidated you know but when it actually travels through solid rock and keep in mind most of the ground it's going to be solid rock the sediment layers aren't that deep uh and I'm going to say real quick just to clarify when I say not that de I'm talking geologically like in the Central Valley we have areas of set that are over 10,000 ft deep so they can be deep by our scale but um in most places they're not too bad you know like in the Central Valley over large portions of it you're really only going to be looking at a couple thousand feet at most over large parts of it unless the closer you get towards the mountains and in places like San Francisco a lot of it you know it's either resting on Bedrock or perhaps you know at most like you know between 20 and 100 ft of sediment so it just kind of depends on you know where you're at our waves are going to be the second type of body wave and these are going to be called ra Raleigh waves now I believe it's pronounced rale I always pronounce it rale I suppose you could try to call it R but I believe it's pronounced rale it doesn't matter as long as you can recognize the spelling of it and these are going to be the weirdest of all ripples so kind of from like an external perspective it would look like the ground is vibrating or undulating up and down as that wave progresses kind of like uh the p waves but the actual motion is a little bit different so it's basic or up and down like an s-wave I should say not a p wve it's basically almost like a combination of an s-wave and a p-wave in that the ground is undulating up and down via contraction and extension uh you know like compression and dilation in a sense uh and it's doing this because the wave motion is actually acting like Oceanic waves and this is something we're going to talk about a little bit more detail when we go into the oceans lab but you know when we look at the waves in the ocean we might see something like you know looks like waves but in reality the direction of the water molecules is actually creating circular orbits so it's like it'll go forward and then it's going to go back and then as it's going forward and back you know that's like that movement of the parcel but the whole thing is going to be propagating forward you know that's why for example if you were to um drop a big rock like in a lake or Pond or your pool you know you're going to see a bunch of ripples spreading out and those ripples are kind of like waves and that water is going to be moving in like a forward upward backwards and downward and then back to its original Place motion and but it's going to also be moving outward now this is kind of weird to really picture you know I it took me a little bit of time to actually really picture how this motion really works but I guess a way to think about this would be like again in terms of the ocean waves so let's say you have a boat in the water and a big wave is coming up behind it and so that wave is propagating forward until eventually it goes underneath the boat now as that wave approaches it's going to kind of pick up the back end of the boat so it's going to be angled right and then as the wave progresses you got like the back here and the front here well that didn't come out well at all back and front anyway so you got like I'll just draw it over here so you got like the wave propagating so it's picking up the back of the boat and then as it raave reaches its height it's going to flatten the boat you know it'll be kind of riding on the top of the curve and then the boat is going to sink as the wave is passing in a sense it's like kind of sliding it down its backside and then the wave passes and it goes back to being flat again and so even though the the boat went up and down and changed its orientation a couple of times you know it ended in the exact same spot it began and that wave continues forward and so the same thing is going to be happening with these Raleigh waves like so you're going to have this pattern of compression and extension as the ground is literally kind of being pushed forward and it's being pushed up and then back an extension until it eventually gets back to its original spot and gets back to its original shape and because this has this like compression you know like this squeezing effect uh and compress an extending effect as well as going up and down this is going to be the most destructive of the surface waves but love waves are also crazy destructive and because they're occurring at roughly the same time frame because they're both relatively the same speed we can't really distinguish them in terms of which one is specifically causing which specific piece of Destruction you know but so together they're the most destructive force so I guess another way to think about this is imagine you're standing at the ground you know and your feet are you know nicely balanced at shoulder length and then all of a sudden the ground is squeezing together so your feet slide together and then get pushed apart into the splits so that would be like that PE wve tape motion but at the same time you're being picked up first by your front feet and then by your back feet you know or so your right foot and then by your back foot while you're you know suddenly starting to do the splits and then all of a sudden you know your you know right foot as it's moving back towards your left foot and your left foot starts moving back towards your front foot you're starting to be dropped down until in the end somehow you're supposed to be left standing now obviously when this is happening on the ground and you went through that it's very unlikely you're going to be left standing and so if you are something solid like a building and you're suddenly getting pulled apart pushed up and down you know and that it's going to be a lot of shaking a lot of motion and it's going to cause a lot of damage now I'm expressing this kind of in an extreme case like I said this compression is never going to be to the point where your legs are slapping together and then going into the splits that is obviously a great exaggeration of that degree of compression I'm just exaggerating it to demonstrate the motion uh often times these levels of vibrations like in terms of the up and down motions might only be on the order of a few centim M or a few millimeters uh it really depends on the strength of an earthquake and I think you'll get a pretty good view of this when you look at the lab because the lab for today there's going to be a video where they simulate earthquakes of different magnitudes and it's basically going to show you a desk with some stuff on it and they're going to shake that desk with the amount of shaking equivalent to the different strengths of earthquakes and when you get to something like a 9.0 you'll realize that it can be pretty intense and pretty big shake so we've gone through you know the four types of seismic waves um and you know they each have their own characteristics but I want you to be aware that when an earthquake happens all of these seismic waves are being released simultaneously so you can imagine that all of that all the different seismic signatures are happening at the same time well kind of you know because each of these size mic waves travel at a different speed then they will all arrive at the destination at different times and we can use that arrival time to determine things like you know the location of the earthquake so I've talked about seismographs and seismograms throughout this lecture um and that's going to be how we actually detect earthquakes and so the principle of a seismograph is basically like we'll go with the original design you know where you basically had a let me get a ink here you know you have the ground and you have like a kind of a table you know that's like anchored deep into the ground and then you'd have like this like little device you know thing sticking up here like a like a hook and then from this hook you would have a like a basically like a plum Bob you know where You' have like a string and you'd have like a little weight with like a marker at the end like something to put in the ink and I'm I have it just kind of hanging freely it would actually be touching the table because over here you would have like a little drum roll here and a drum roll here like a for cylinder paper uh and so the idea is that you know you're constantly like rolling the cylinder paper you know underneath it and so if the ground is perfectly still it's just going to create a straight line the paper is just going to go freely you know underneath that Plum Bob but um this is where we uh can actually detect earthquakes because of um you know Newton's Laws of Motion so when an earthquake occurs you know it's going to shake the table a little bit and as it's shaking the table a little bit you know that that motion will translate up through this little hook which is part of it and so the whole table is going to shake but that plumbob that's floating on the string that's going to not react as quick because of um you know the first law of motion the law of inertia you know which means that it's going to want to resist that motion um you know kind of like the principle you know where you have like a tablecloth with like you know some glasses on it and if you pull the tablecloth out quick enough the glasses will stay put it's the same principle so the idea is that the table is going to shake but that plumbob is going to want to stay put for a little bit and so as such you're going to be pushing the paper around and that's going to create these like up and down marks which is representing the degree of that shaking and so I also mentioned that you know these different seismic waves can travel at different speeds and you know where the p waves Ares first the S wav second and the surface waves arrive last now each of these do have like kind of a specific you know shape in a sense like your surface waves are going to be your big ones and your p waves are going to be smaller than your s-waves um but and your p waves will arve first so you got like that straight line representing no motion and then you got your then you say oh this is when my hewa first arriv and so you're going to take take that measurement you're going to say that happened at exactly this moment in time and then you're going to say Well when did the sway first arrive I look at that big jump right over here so you're going to make a mark there and say yeah that's right here actually and that's exactly when the SWA first arrive so that's going to be your lag time you know lag time something we're going to go into shortly uh and then you use your uh your surface waves like the height of your surface waves to determine the magnitude of it you know your La time plus the height of those surface waves and so with all this information you can determine the location of the uh epicenter as well as you know the strength of it we can determine Lac time because we have a pretty good understanding now of how fast p waves and s-waves move so let me kind of make a kind of a reverse example you know using distance so let's say you know you know we're here and we're like all right we're going to do a drag race from here to LA or whatever and I'm just going to say you know it's just some distance away and so um you know you guys are in your cool new Tesla and I'm in my old jalabi and we're both starting off you know at the same place so I'll put a y for you and an M for me now your cool Tesla is going to be able to you know easily handle 100 miles an hour whereas my old jalap is only going to handle 50 m an hour and so we're going to drag erase this whole distance which means that we're going to be putting a pedal to the metal and we're going to go now after 1 hour you know you're going to have gone 100 miles right because you're going 100 miles an hour whereas me I'm only going to go 50 miles because I go 50 mil an hour and so you know there's going to be a difference of 50 miles after another hour I'll use a different color here after another hour you're going to have gone 200 miles and I will have gone you know 100 so in that regard this distance between you know where I am and you are is now going to be oh let me draw that line again is going to be 100 miles like every hour you travel there's going to be an increase in the distance between us by 50 miles so like after hour 1 we're 50 mil apart after 2 hours we're 100 after three we're at 150 so you can kind of look at this distance as a proxy for lack time because the p waves are able to move so much faster the longer they go the more or let me phrase this the farther they go the more more time there is going to be between the p waves first arrival and the S waves first arrival so with this data you know we can calculate out this slck time between the p wve and the swave you know when they arrive and we can say all right if if there's this much time difference and since we know how far or how fast each of these waves are going we can then calculate out the distance and once we can calculate out the distance of that then we can plot you know that distance on the map and if we repeat this many times you know with many different you know seismic graphs then magic we'll know exactly where that earthquake occurred let me kind of demonstrate this all right so let me make a really poorly drawn you know United States you know very poorly drawn now let's say we have three seismographs we have you know one over here one over here and one over here just just arbitrarily saying and there is an earthquake and that earthquake is being picked up by the seismogram by all three seismograms so we calculate out the Rival time let's say you know we'll go with this guy first and so uh we say all right based upon the lack time we know exactly how far it is it's going to be you know so many hundreds of miles now the thing is is that seismogram that lack time cannot tell us where it occurred it can only tell us the distance but it can't tell us the direction so what we would have to do is we'd actually plot a circle around that a seismograph that would indicate you know the that distance from it so we don't know where on the circle the earthquake occurred all we know is it had to have occurred somewhere around that Circle but here's the thing like we have three different seismograms here so if we were to um do the same thing for this guy down here you know and we were to do take the third guy and we were to do something similar there which would be a much bigger one and of course I'm not drawing these as perfect circles then we can narrow it down we can triangulate it and the reason for that is because we don't like I says they don't tell us where it's at they only can tell us a distance so we know that uh it has to be somewhere on this line here let me use a different color here somewhere on this line somewhere on this line and somewhere on this line but since it has to occur so there's there's two rules that have to occur one is it has to occur on that line and two it has to occur at a point where all three lines are touching you know because all three sides my gram felt it which means it has to be at some point common to all three circles or in other words it has to be at the point where all three circles touch now I kind of Drew this freehand pretty poorly but you can imagine that it occurred like right here you know that that's where all the three circles are touching and so um that's that would be how we would identify where the earthquake is uh and this is effectively how we do it right now now in reality you know we don't use those little drum roll seismograms I showed you we actually have lasers and things to make it much more accurate and we have computer programs to plot these things uh utilizing not just three but thousands of cagrs or at least hundreds you know depending on how strong it is so you know we have a pretty accurate measurement of where it's at although sometimes they do have to make adjustments because of like you know calculation error uh but it's a pretty cool and pretty accurate science in fact this is the whole principle of how um GPS works because like uh if you guys didn't know GPS works by basically you have these satellites in space and all they're really doing all those GPS units are doing are constantly sending out a signal saying the time is now this the time is now this the time is now this you know it's just constantly telling the time and so you have on your phone like or whatever device you have that has GPS you know you have a program in there like a little sensor that can actually pick up those signals and it says like okay well um this satellite a is telling me that it is this time but my internal clock says that it's this time which means that there's been this much of a time difference and as part of their programming they know exactly where each of those satellites should be at any given time you know all that information is pre-programmed in and so they say all right since it is since that's how like is saying it's this time and I'm receiving at this time I can kind of create like a big circle of where it's of where I'm at and relation to that satellite cuz the program knows where that satellite is at that exact moment it sent that message out and then it listens to another one and a third one and it can triangulate and create it you only need three satellites to you know actually get a measurement of where you're at uh nowadays we usually have like 16 or so that are going to hit your phone because we have a lot of them up there to make it more accurate and there are of course confounding issues like the magnetosphere which is going to interfere the time and we have other Co Technologies to stop that and if you're interested in knowing more how GPS works then you know please ask me and and I'm happy to go into it in more detail but the principles behind triangulating your location with GPS and using seismograms to triangulate the location of the earthquake is effectively the same okay so we now know what an earthquake is we now know you know the different types of seismic waves that are used to created and now we also even know how to take those seismic ways and even figure out exactly where it originated pretty cool but geology is a science and science likes nothing better than to try to put numbers on things so it's a very quantitative field of study so you know now that we understand what earthquakes are it might be nice to be able to put some numbers to what an earthquake is like so we have an indication of just how big the earthquake was and so we have two different types of measurements that we can take of an earthquake and the the first is going to be a measurement of its intensity in other words it's going to be a measure of you know the not just so much the amount of ground shaking but basically how much property damage there was and the other measure is going to be a measure of the magnitude of the Quake so it's a measure of how much energy was released by the earthquake and the magnitude scales and there's two of them are going to be the more recent one and we're going to be talking about each of these in a little bit more detail so in terms of intensity measurements we use something called the mer modified mercal intensity scale originally it was just the meral intensity scale that was developed in 1902 but you know since then we've modified it a whole bunch now this has been used in historical records and so a lot of our records use it and quite frankly I just don't like it because it's too subjective and it's two based upon property damage as opposed to the actual destructive potential of the earthquake meaning an earthquake that occurred in the middle of a giant farm field you know in the Bread Basket you know you're not can get what might be big enough to destroy San Francisco but it's going to have a smaller number because it did less damage because there's less stuff there so to speak there might be nothing there to break now this scale it is a community internet based system and it was developed by the USGS um so originally it was basically recorded where you had geologists and professionals from around the you know the area go in and you know record what they consider their damage and then people could call in nowadays we have the internet in fact a couple of years back we had an earthquake and it was it wasn't that big of an earthquake but I did notice that in a admittedly old part of my wall uh I notice a tiny little bit of crack formed in the alabaster so I went online and recorded it and uh and you can just go to like USGS like Google USGS reporting earthquake and it'll take you right there and so the scale right now is entirely based upon user input and the idea here is that you have like a a bunch of numbers and like and these numbers are measured by Roman numerals where like one is like you know the lowest and it just goes higher from there and the idea being that one is no damage you kind of felt it there was some shaking you maybe something fell off a shelf perhaps you know but nothing really and and then as you go higher you know it finalizes at the highest level with absolute total Destruction like the buildings are just Rubble on the ground the reason I don't like this besides the fact that you know it assumes that you have um property to be destroyed is that it's also subjective and it doesn't take into account the engineering of those buildings so for example I might say I might look have an earthquake and look at the damage and say well based upon you know my educated expertise so I'm coming as a geologist you know I I should have a greater knowledge I say that this might be a three on that scale and then a buddy of mine who is equally educated might look at that and say you know what no cuz you know I'm looking at this and I think it's more for and we could argue this back and forth and and there's really no way to say who's right and who's wrong right it's a very subjective thing I'm seeing a three level of damage he's seeing a four level of damage now there is something in statistics called the average of large numbers and the principle of that mathematical law is that in principle I'm going to say Theory but I should say in hypothetically you know in principle um if you you know if you have enough people saying these different numbers then the average of all those numbers should be a pretty close approximation to the truth you know that the people who are way off will be outliers and kind of get discounted and so you know if enough people if half the people are arguing a three and half the people are arguing a four you know it would argue it as a three and a half and there's a good chance that it's probably somewhere in there you know so that's called The Law of large numbers but even then I mean this is based upon the interpretation of a bunch of people who are just normal people in the community now ideally you know when you decide to become dual majors in geology because my class inspired you so much and you take a whole bunch more courses in geology you should be able to make really accurate measurements but who's to say now to be fair right now on the internet the USGS is aware that you know the normal people in fact a lot of geologists for that matter is not going to know off the top of their head you know the difference in destruction between a three and a four on the modified morol scale so usually what they have is they have a number of specific questions you know and you know you input these answers you know usually from drop- down menus and based upon the answers you're inputting from these drop- down menus then the system will calculate out what that number should be based upon your reported deg uh level of Destruction but like I said it also doesn't take into account engineering meaning like let's say I had a house that I put together out of um Rusty Nails and driftwood from the ocean and I decided to build it just to have it just sitting on a pile of loose sand and then you who are much smarter than me decided to build a brick house well actually not a brick house let's say a woodh house which is even better and you have it anchored to concrete that is anchored deep in the ground but you also have you know it being you know kind of loose wood you know you have a little bit of give between the parts you know with like a rubber type spackle so they can kind of compress and extend a little bit now when an earthquake hits you know my house is just going to be ripped to pieces because it's poorly constructed it's put together with Rusty Nails so I report oh no total Destruction you know whereas you'd be like um I I guess a picture fell off the shelf I suppose okay you know and that's the case like yours was engineered better so in California all of our buildings are engineered to withstand earthquakes to a certain intensity you know we're designed to actually weather a certain amount of shaking and we do this because we don't want to have to rebuild every city every time an earthquake hits but even knowing that engineering the type of material makes a difference like if you're in a brick house you're more likely to develop of damage than if you're in a woodh house because wood has a little bit give to it and that makes a big difference uh whereas brick it's it's solid it's brittle it's more likely to just break you know if I were to you know take a stick and you know hit it and try to bend it or try to squeeze it I could actually bend it a little bit before it breaks whereas if I try to do the same with a rock like a dry let's say like a dry spaghetti noodles it's not going to really Bend it's just going to kind of snap so because of these Reasons I'm not a big fan of the modified marol intensity scale and as a geologist I'm like I just let it drop but I have to be fair I got to be true to all sides and I will say it is really good scale for engineers Engineers use this scale in order to better understand to what level they have to engineer their buildings to withstand earthquakes so in my opinion from a geology perspective it's kind of meaningless it's not super useful but if I was an engineering Professor I'd be saying this is the greatest scale ever this is the scale that everyone should be using yeah awesome scale awesome and that's why it's still in use because different professions do have a definite need for it the first measurement of magnitude you know like the size of the earthquake that was developed is the RoR scale and I'm sure everyone here has probably heard of the RoR scale usually when you have an earthquake the news will report things like it was a 7.0 on the RoR scale or whatever um now pretty much in common speak no matter the type of magnitude system we're using magnitude measure we almost always just simply call it the RoR scale it's just common parlament and except for extremely large earthquakes the difference between the different magnitude scales is effectively meaningless they're they will generate usually the same number it only starts to differ when you deal with really really really big earthquakes um or you know potentially earthquakes from Super far away now because you know the RoR skill is only eable up to a certain distance from the original earthquake but it's a pretty big distance so the RoR scale what it does is it's basically looking at the amplitude of the biggest wave or seismic wave so remember those seismo graphs that I was showing earlier you know where you'd have like you know like you got your little p waves and you got your slightly bigger S waves and then you had all those big old surface waves or whatever you know like what it does is it takes a look at the biggest wave and then it takes that measurement you know like the height of that and they're able to use that to figure out um you know the scale and so I'm not going to go into too much detail and like how that translates I'll talk about it in a moment just a bit but the important thing about the RoR scale is that it is a logarithmic scale uh I don't know if you guys remember this from your math class but the log scale is powers of 10 so like if you have a base 10 you know unless you specify otherwise log is always considered base 10 and so like log one is 10 log 2 is 100 log 3 is a th000 you know you're always increasing it by 10 fold so in other words if you had a 6.0 earthquake and then you had it followed by a 7.0 earthquake that 7.0 earthquake would be 10 times the size of the 6.0 earthquake if you had like a 8.0 earthquake that would be a 100 times the size of that 6.0 earthquake if you had a 9.0 earthquake it would be a thousand times that 6.0 earthquake and keep in mind that a 6.0 earthquake was felt in Fresno from a great distance away a 9.0 earthquake is like a city Buster I mean it's it even with good engineering those buildings are still going to be incredibly damaged and California isn't really engineered to withstand 9.0 earthquakes because in California were not really expecting them but if they if and when they do occur it will be crazy destructive now I'm not going to go into the physics equations behind this I'm just going to ask that you accept that um every increase of one on that scale is going to be a 32 fold increase in the amount of energy released so in other words the um amplitude of a 7.0 is going to be 10 times bigger but in order to make that amplitude to 10 times bigger it's going to take 32 times as much energy to do so now the problem for this is of course when you're starting to deal with really big earthquakes and it there's actually some technical difficulties and I don't want to go into all those details they're just not at all important for this class but I will simply say that if you're dealing with like 8.0 and 9.0 earthquakes this scale starts to get a little bit funky so and actually in some cases you know even a little bit smaller than that and the really big earthquakes are the earthquakes that we really want to have that accurate measurement because we can use that to help formulate and predict other future potentially danger Dangerous earthquakes so this is another picture of a seismic graph you know you have your p wve and you have your swave and so you know we use that PS time difference you know to calculate out you know the distance which is important because remember how I said the energy these sizing waves are losing energy as it goes farther so it makes sense that the amplitude of the Waves will get smaller the farther weight you get so we can use the you know the SP time difference you know to calculate out that distance and then we know how much we have to adjust the size of those waves like how big those waves would really be um and we take a look at the waves and we calculate out this biggest wave and we say all right the biggest wave is in this context you know 23 mm above the Baseline and then we go up from there now the actual process is kind of cool and I'm going to kind of showcase this on the next slide so the way we used to um solve these things like the magnitude of an earthquake was kind of weird so you you'd have like a ologist in an office who would be U asking for those like seismic distances from all these different groups so they'd say all right right now we have a PS difference of a certain amount of time and so you'd have these basically these three lines going on um let's try to draw this so you have something like this like this and like this and so on this line table you would have basically different p PS interview time or Ps interval times so like what is that time delay and on this scale you know over here you would have different you know so I'll call this time on this side you have amplitude of the wave on this side you know that thing you measured from that seisa graph and then you would say all right the P the PS delay was this long and it was you know that amplitude cool and then what they would do is they would say they contact like another seismic graph you know another station that had a seismic graph and they'd say okay well what are your PS delay and what is the amplitude and they'd say oh well it's something like this and then oh it's oh I guess I deleted the first one oh already draw it sure it's a little off and let's go with the third one and this one is something like you know this and this one is you know something like this and if you notice I mean I'm kind of drawing these world they're all bunching in the same area but the idea is you take a look at you know where all these things are crossing because we have a scale you know like where this lines cross is going to be the amplitude so for this wave it would be this amplitude for this wave it would be this amplitude you know so on and so forth we take all those different or not amplitude magn magnitudes so this is going to be your magnitude line and we do this for you know usually like at least six seven eight you know different lines we average them together you know because that again law of large numbers that helps take into account like that um error and uh and then that number is going to be the magnitude like cuz the apparent magnitude of the earthquake will be different at each of these sizing stations they should all be close but they'll be slightly different because the amplitude is going to be different based and the you know time difference is going to be different now that's how we used to do it and this principle was exactly the same and we know exactly like what magnitude should be on this scale because we've done a lot of rigorous testing it's all been mathematically proven and and this is how we used to do it like I said but nowadays this is still the function of what we're doing but we have computers that are doing it you know we have a bunch of these stations that are always feeding this information always always always feeding this information into these C computers in different locations because you know you got backups and then it's constantly calculating it out you know and while it's calculating out the magnitude it's also calculating out that epicenter you know or that focus and that's how we know exactly how big an earthquake is and exactly where that earthquake is the moment magnitude scale is the other magnitude measurement and it's it's the newest one it's the best one it's you know we should all like you know clap our hands and seeing its braises because it is a great scale and in fact often times this is what's really being calculated but when it's being reported to the public we just call it the RoR scale because everyone knows what the RoR scale is not everyone knows what the moment magnitude scale is now the moment magnitude scale it is a little bit different because it's not just measuring that amplitude it's a measure of the total energy that is released um so it's a function of like the energy of that wave as opposed to the size of the wave and we calculate out that energy based upon like the displacement how much did that ground move you know that that displacement we talked about um where exactly it moved because one of the problems with the RoR scale is things really far away started becoming problematic so we are better able to take that into account and also how strong was that rock when it broke you know and so the general uh readout is for most earthquakes almost all earthquakes the moment magnitude number will always be the same as the RoR scale number but when you go into like the really really big earthquakes you're going to see a Divergence because the RoR scale is always going to underestimate it and so the moment magnitude is actually a little bit more accurate and we were able to prove this at this point so it is the better scale and in that way I showed you how we calculated out the magnitude of a of the earthquake that was developed for the RoR scale but the principle still applies to the moment magnitude scale but now we can also throw in like you know some more just raw calculations you know and so it's it's pretty cool it's it's surprisingly accurate so just something to keep in mind the moment magnitude is the best most recent most accurate measurement scale it is commonly called the RoR scale the RoR scale is specifically based upon the amplitude of the wave the size of the wave it's the RoR scale is less good on the biggest waves but both of them are going to measure the magnitude magnitude is like a funny way of saying size it's a it's a different way of measuring the size of the earthquake it doesn't care what destruction occurred you know it doesn't matter it's just about the actual size of that earthquake itself since we understand you know what an earthquake is and how to calculate it out and all that other good parts I figure it's now time to talk about the damages that earthquake can create so the amount of damage that an earthquake can create is going to be primarily a function of you know the magnitude of the earthquake the bigger the earthquake you know the more damage it can do in addition the distance from the focus or the epicenter depending on how you want to consider it is going to be another issue so between 20 and 50 kilm from you know the epicenter is all going to have about equal amount of shaking but after that it starts to diminish and it starts to diminish very quickly after 50 km so 50 km just to put this in perspective would be about 30 m um something else that's kind of fun when you deal with a lot of science you know science is always done in metric so you get kind of used to if you're a teacher you get used to converting metric to you know American now another thing that actually influences the amount of damage is going to be the subsurface so things that are built or areas that have a lot of sediment a lot of dirt are going to generally you know have an amplification of the damages it's going to be felt a little bit more strongly areas that you know for example if you have an earthquake in a very stable interior uh that damage is going to be felt less but because that in stable interior it's usually going to be a you know nice s or hard rock you know that Dam those waves are going to be able to propagate farther so you're going to have have you know a little bit less shaking sure but that shaking is going to be able to travel a bunch farther now the amount of damage is also going to be a function of like I said the magnitude the intensity of it but also the duration you know so for example let's say you had like a major bump but it only lasts one second that's going to be a lot less than something that lasts longer but it's smaller so let me uh let me kind of express it this way let's say um you have like I I have a table and I have a bunch of glasses on it and whatnot you know uh and I take the table and I shake it 3 in to the front of me like like in front of me and then I pull it back you know those 3 in again so I moved at 3 in but just boom boom one second has passed I mean there's going to definitely be some motion I might even top over a glass or two right now let's say instead of doing those 3 seconds I only move it or 3 in I only Move It 2 in so it's going to be a weaker level of shaking but it's it just being once forward and once back I just keep vibrating it back and forth for like you know two minutes in the end even though it's less shaking those glasses are going to be vibrating all over the place they gonna fall off the table you know they're going to there's just going to be more damage um in fact uh it's going to be one of the weird truths about it is like you you're going to have greater damage the longer it shakes but you could also mitigate that by having lesser intensity so I uh I I knew someone that was studying earthquakes in South America this one part of South America and in this one area there was a fault and they were actually expecting it to get like a 8.0 or 9.0 earthquake like their statistics showed that it was imminent you know and so what they did was they created um they put in you know a seismic graph like a thing that was measuring the shaking and was report you know sending it to satellites and you know being recorded back to them but they also or um not to satellite sorry to a a local cly computer computer so it would record the data and then they also had a device that was basically like a couple of big receivers with lasers and all it did was more or less measured how much motion there was on the fault like you know so it begins where they were you know directly touching each other in a sense and so they can measure like when they go back after the earthquake they could see how far those two things separated from each other to get an idea of the displacement and so after a year you know the thing reported no earthquakes and she thought that was odd she was almost certain that there should have been something even even if not a big one there should have been something so she goes out there and you know looked at all the data and discovered that there wasn't really one giant earthquake you know like we moving it it was actually like a really it was well it was a giant earthquake but it was a very slow one so you know based upon the amount of displacement it should have been like a 9.0 if it happened over the course of a couple of minutes but instead of it happening like like a couple of minutes and it moves like you know that distance it took about an entire year to move that distance for whatever reason the Rocks gave away in a way where it was sort of a continuous series of micro earthquakes and so in that case you know you had a very low intensity but a very long duration so that actually made much less damage um but to be honest if you were a building sitting on that fault you still would have been torn apart because even though it was a very low intensity the duration would have still ripped that building in two you know less shaking but more displacement on top of all of this you can consider the nature of the surface materials or the building materials you know this is a picture of a bridge that was designed to stand an earthquake so you know you have instead of it being one solid construction anchored firmly in the ground you know they actually have the frames of course anchored firmly on the ground you know these tall bits you see here but they then have uh the bridge actually being suspended from wired cables and then they actually made the uh Concrete in the road they formulated it in a way to actually have a little bit of give so when an earthquake happened the bridge itself you know would Shake but it was designed to withstand a certain amount of shaking and as you can see in this picture quite a bit of shaking and and so in that context you know it's not going to break it's going to shake but it's not going to break apart construction practices also make a difference you know um and and we actually see this in places like San Francisco so when you're in an earthquake um or when you're in a tall building in an earthquake you know that building is going to start to shake and the higher up you are on that building the more intense the shaking it is um so kind of picture this like go find uh like a pencil or a pen or something and kind of hold it by a tip and just kind of move it a little bit you know in your fingers holding it by the tip and you can see that the top of the pen is just moving a lot more than the bottom of the pen same thing is going to happen with skyscrapers so they do two things to these skyscrapers in cities like San Francisco or LA or Tokyo you know to help prevent some of of damage the first is instead of it sitting on like a solid concrete base you know you know in the ground they actually have the building sitting on Springs and of course the Springs are attached to a concrete base that's anchored in the ground you know but the idea here and these are espcially designed Springs where it would take a lot of shaking like a lot of force as an an earthquake to move it but the idea is as it's shaking instead of having the building cracking into the concrete base it's able to go up and down a little bit on these Springs and these Springs of course being super tight are going to absorb some of that earthquake energy in addition they actually designed the buildings themselves to sway to shake back and forth or whatnot and they do and they have the building constructed of materials that can withstand this so it's moving back and forth um but you know like the bridge it's able to withstand that shaking and of course as it's shaking every time it moves you know from one side to the other uh the construction materials are absorbing some of that earthquake energy so you're diminishing the intensity of that wave meaning that it's going to be you know less destructive now there is one design that uh has been considered in some places and it's basically putting a giant gyroscope at the top of these buildings to kind of create a like to use a motor to create like effectively a counter wave to help display some of that energy I don't know if that's being used in practice I I don't I'm not familiar with current engineering practices enough to say if that's currently in use but I do know that it has been considered and the principle is solid for example like uh our gigantic boats you know like our Naval destroyers or whatnot you know like the super big ones they alha will actually have a gyroscope in there so that they don't ever sway too much in the waves they generally will stay upright and so we have these things engineered pretty well um and like I said earlier you know like um materials that are flexible are going to survive better than materials that are not so earthquakes can occur in you know anywhere I mean I I said most of them are going to be in that ring of fire earlier let me uh point that out for you uh let's find a good color so this oh that's not a good color okay uh this is going to be the ring of fire you know that's that circum Pacific ring this is going to be the Mid-Atlantic Ridge and technically speaking you can imagine it kind of going along Antarctica which is beyond like what we can see in the picture and includes this and this um things like that so that's that's like a really big diver a bunch of divergent boundaries that are kind of connected together uh and then the ring of fire in the center is going to be a bunch of conversion boundaries and so if you notice like uh the L is showing those play boundaries happens to be the a place where you have a lot of earthquakes you also got this thing here and see here where you have a bunch of earthquakes and that's going to be uh part of that circum Alpine himan belt kind of continues on into here and that's going to be where you know uh Africa and Arabia and India are all colliding with Eurasia so that's again Continental Continental Collision so it's another convergent boundary and so every dot you see here every color dot is representing an earthquake um given the amount of dots I see here it's probably measuring relatively intense earthquakes I mean not necessarily intense enough to you know feel super strong but you know probably more than 1.0 maybe like a 3.0 or higher if you go on the USG site you can actually go on find their earthquake tracker and you can put like a time frame and it will actually show you where all these earthquakes are and you can put a filter on it to say like I want you to show me where every earthquake is on Earth in the last 24 hours of this intensity or higher it's pretty cool and you'll be surprised just how many earthquakes you see every 24 hours so the uh like the summary of this of course is that almost all of these earthquakes are going to be associated with play boundaries you might notice and I'll use this in purple you know you got some earthquakes here that's going to be you know you got some in a few other similar places like here these are going to be intracratonic earthquakes and there's a fully different phenomenon at work there and I'm not we're just not going to worry about it we're going to pretend it doesn't exist because it's very few of the earthquakes um so you can see that most of these earthquakes are going to be associated with that you know plate boundary and these earthquakes are actually color coded to match how deep they are because remember how I said when we find their focus it's not just you know in two Dimensions like on a map that's usually how they uh announce it to the world like on the news but we can track it in three dimensions so we know exactly how deep it is so basically red is going to be shallow yellow is going to be intermediate and blue is going to be deep so if you notice um again I'll change the color real quick like right here that's not a good color let's try this one right here you have a bunch of shallow earthquakes and that's going to be things like the San Andrea's fault it's going to be a uh and you also have a bunch of shallow earthquakes here and here you know basically those places I was saying are those uh mid ocean ridges those so Divergent and transform faults you know or or um transform um boundaries are almost always going to have relatively shallow earthquakes your deep ones and your intermediate ones are going to be at convergent plate boundaries and so if you notice how you have like um like in South America like right here you can see how it begins shallow on the outside of the KET and it's getting progressively deeper as you go inside you can kind of see the same thing going on there where it's shallow on the outside getting deeper same thing with Japan sh on the other side going deeper and that's because of that descending plate you know you have your continent here and your ocean here and as it's descending down the earthquakes which are going to be following that plate are going to get deeper and deeper and so we call that plane of descending earthquakes the wadad Ben off Zone that's the technical term the Wadi Ben off Zone but in pretty much all parament even amongst geologists we just simply call it the Bening off Zone usually as a shorthand and so you can see here where you have like your overriding lithosphere like you're overwriting continental plate uh let me change the color know like right here and you have your ocean plate and it's descending and so as it's descending you're going to have earthquakes along like where it's basically scraping you know that that uh country rock the rock above it CU remember an earthquake is caused by the release of energy as um as the rock breaks like like as as it's trying to be pushed down uh the rock is trying is adding stress you know you're adding energy as The Rock is being pushed down and eventually stress becomes so big that it's stronger than the Rock and it breaks and releases that energy and so where is the Rock going to break it's going to break at the interface of the subducting plate and this they rock over it which at first is going to be the continent that'll be your shallow stuff but as you get deeper it's going to be your like athenos spere or uh sorry your mantle with a sphere you know and uh and that's going to be your deeper you know your intermediate and your deeper ones now not noce how this is drawn kind of raggedy and that's mostly because in all practicality it's going to start undergoing mineral phase changes and it's going to be buied by certain convection currents so it's never going to be a perfect you know even slab as usually drawn and eventually you notice how it looks almost like it's dripping here and that again has to deal with um phase changes where like you know it becomes denser because of the phase change and then the rock is cooler because you know it's coming from higher up it's much hotter than it was on the surface but it's still going to be cooler than the surrounding Rock a little bit so it's going to keep sinking until eventually it could drip potentially to that core mantle boundary you know that's what we suspect now and so you can tell from the distance here that this can be quite deep you know uh like the deep deep earthquakes that happen in the transition zone notice how that is going to be like 600 km deep I mean that's going to be somewhere in the neighborhood of 350 370 I I I don't want to do the mental math right now miles that is deep 360 miles okay I did the mental math um and um gosh I can't wait I just did that Mental Math um now it doesn't show here but you'd also have your volcanic Arc going on like right here put it in red your volcanic art going on right here from the partial melting at this level um and notice how the deepest earthquake is only at you know somewhere within this transition zone but the slab keeps going down so in theory you should have more earthquakes right as you should keep having earthquak as you keep going down so the question becomes why don't you have earthquakes you know when you're in the lower mantle and actually the lower part of the transition zone for that matter and let's consider that for a second okay yep I sing badly too don't worry um the reason you don't have it in the lower mantle and in the lower transition zone for that matter is because that's the point where you start going into like the asthenosphere you know where the rock is no longer have the ability to break it's always going to flow now you can get to a point in that transition zone where some of that country rock some of that outside Rock might start have flowing properties you know some slight flowing properties but the downo rock is going to still be comparatively colder and that could change the local thinger it might cool the surrounding Rock enough that it for a moment it has some brittle properties and then break you know so you got some weird things going on there but that's how you can have your deep ones you know it's because it's going Inland but when you get deep enough you're just never going to have earthquakes because the rock can't break it's like Playdoh it's just going to ooze and flow so that's going to be it for this week um hope you guys had a lot of fun with this particular lecture uh so as a reminder you know make sure you post on the discussion board after watching this uh and then you know I would do the homework and do the lab following that and uh if you have any questions about the lab or you want me to look it over you can always email it to me ideally before Friday so I have a real chance to look it over um if you have any questions about any of this then of course always let me know now next week you know I guess said at the start we're going to be going over like the rest of earthquake stuff which is just a few slides that goes over a few of the hazards like liquefaction you know which would be like quicksand tsunamis things like that uh and then after that we're going to have um a bit of a lecture on topographic maps it's just to be kind of a bit of information to help prepare you for the uh the actual lab uh the lecture next week will be running short so it'll only be about an hour worth of lecture or actually sorry it'll be closer to two hours worth of lecture uh is my estimation and then I would recommend after you do the lecture you do the lab and then there is going to be a test next week now the test is going to be over everything we've covered so far you know including this lab and including the lab and lecture next week so make sure you do all of that before you do the test the test is going to be 50 multiple choice questions uh it'll be in a style very similar to what you saw in the practice test if you look at the overview page in the the module uh and it's set to be about an hour I I'm going to play with the settings and see if I can give you guys um a little more time because I like to give a little bit more time for these online tests but when I originally wrote the test it was intended to be a a 60-minute test so with that in mind your next week will only have you know be the same six contact hours although the lab next week usually takes most people like maybe two hours so you guys should have a little bit of extra time to study I do recommend taking a little bit of time the rest of this week as well as next week before the test to go over your notes to you know prepare yourself uh do some studying because that is the best way to get a good grade there are four tests as just a reminder there are four tests this semester and I will drop the lowest but that means there going to be only three tests that are red plus the final exam which means every test is worth a lot of points like like the test will be worth about 10% of your final grade so it is extremely important for you to try your best if you mess up like I said I drop the lowest but um but you can really try to get a good start you know and trying to get that solid a you know or or B by just putting in a little bit of time you know this week and next week and stud study along those lines uh I want to remind everyone about the extra credit opportunity of creating a study guide because it has been my experience that people who create study guides on their own do much better on the test than those who don't and so to help incentivize you guys there will be an extra credit opportunity to create your own meaning next week when I post the um test on the module uh the following step after that will be kind of like an assignment but it'll be a place for you to upload your study guide if you've made one now if you didn't make one or you don't want to upload that's fine it won't come against you it's going to be nothing but pure extra credit but it will be uh a way for you guys to earn a few extra points and the way I deal with extra credit like that is after the last test has been brought in I will take all of your test scores and I will do some statistics on them on a class level to determine things like like does do I need to apply a curve because I have a standard policy that if the class average on a given test is less than 75% I will curve everyone's grade up to make the class average 75% and I will often look at a lot of the individual questions and if I find that an individual question has you know like 70 80% of the class getting it wrong then I will assume that maybe I did not do my best job at teaching that particular question and I will give everyone the points for that question but that doesn't come up very often uh and to be honest it's actually pretty rare that I actually even have to curve a test up so don't count on you know those points but uh the best you can do right now would be to work on that extra credit you know study guide as well as just study yourself a lot and whatever those extra credit points you will get uh will be applied directly to the test at a slightly later Point meaning after I've determined if I need to apply a curve or whatnot um I will then go through and look at all the extra credit points you've accumulated for that unit and I will simply add all of those points directly to the extra credit sorry sorry let me rephrase that apply those points directly to the test now there will probably be a second extra credit option which I'm working out right now that will also be available after the test so uh kind of keep an eye out for that uh and that'll occur next week after the test and so both will be found on the module next week after the test is posted and of course there'll be some more information about the test next week so again if you have any questions whatsoever then you know reach out let me know email is the primary form of communication um or you can post it you know under announcements or on the Q&A and I'm very happy to answer you guys so like I said I think that's going to be it um had a lot of fun and I will see you guys next week bye