[Music] hi students this is mom day again and today we will be trying to use your previous knowledge of the types of seismic waves in order for you to locate the epicenter of an earthquake at first you will think is it really possible to locate the epicenter of an earthquake but don't we need special materials for us to locate epicenter actually given some data you can already identify or locate the epicenter of one earthquake and we will be discussing it today now what method will we be using we will be using what we call the triangulation method why is it called triangulation method because just like a triangle we're wherein a triangle has three sides in this method you need three different seismic stations for you to get a point of intersection just like in this image this image is provided in your module as you can see we have three circles one showing the seismic station found in bohol the second a seismic station found in negros oriental and third a seismic station found in cebu so once you have data coming from these three different seismic stations you can get the point of intersection of the three circles you have drawn and that will show you where the epicenter of an earthquake is just a short recap of what we have discussed in the previous video there are two main types of seismic waves and those are body waves and surface waves body waves has two subtypes and they are primary waves and secondary waves while surface waves have two subtypes as well which are love waves and rayleigh waves now going back to the two types of body waves which are primary waves and secondary waves since these waves are the waves that can travel through the interior of the earth then these waves play an important role in identifying the epicenter of an earthquake how because we know that primary waves travel faster than secondary waves this means that p waves will be received earlier in the seismic stations than the s waves therefore there will be a time difference this time difference will help us identify the distance of the epicenter from the three seismic stations now i will be showing you a demonstration on how to do the triangulation method in this video i will be using a different set of data which i have used in my previous classes so here we have a map of the philippines and i have data for three places which are iloilo naga and tarlac first what materials will you be using you will be using a drawing compass however if you don't have it you can improvise using a pencil and a string also you will be needing a ruler and if you have an extra pencil or a ball pen you will also be needing it for calculations so there the three seismic stations that we will be using for this example or demonstration are iloilo naga and tarla so we are also provided here the time difference between the arrival times of p waves and s waves and the distance of the epicenter from the seismic station why are these important because that distance of the epicenter from the seismic station will serve as the ray juice of the circle that you will be drawing in a short while so one important thing to know here is that the computed distance of the epicenter from the seismic station is the actual distance which is in kilometers however we are trying to draw this on a smaller scale so therefore we have to convert this into a smaller length using the given scale the given scale is 1 centimeter is equal to 100 kilometers very important this scale only applies to this demonstration other maps will have different scales just like in your module so you will be using another scale for your module so we are given the following data so we are given the data for iloilo we are also given data for naga and we are also given data for tarla [Music] what are these data for this data that i'm talking about is a distance of the epicenter from these respective seismic stations so for example for iloilo we have 520 kilometers and then for naga we have 320 kilometers and for turlock we have 280 kilometers our scale here is one centimeter is equal to 100 kilometers again very important this only applies to this example or this demonstration in your module you will be having different scale other graphs or other maps would also have different scales how do we convert this using the scale so we have to multiply our distance by [Music] 100 kilometers in the denominator and one centimeter in the numerator in order to cancel the kilometers so we can simply do this mentally so 520 divided by 100 would be 5.20 centimeters we will be doing the same with naga and tarla [Music] [Music] now these three values would be the lengths or the radii that you will be using in drawing your three circles you can record this on the third column you can find in the paper that i am showing in the demonstration [Music] now after recording this data it's time for you to mark these places in our map i'm referring to iloilo naga and tarlac so make sure you know your geography next starting with iloilo draw a circle with a reduce corresponding to the distance of the epicenter from iloilo which we have computed a while ago and that is equal to 5.2 centimeters make sure you start with zero [Music] once you have measured the radius use your drawing compass or your improvised compass to draw a circle [Music] that's it you're done with the first circle now do the same with the second and the third circle using the data we have obtained do [Music] that's good [Music] [Music] [Music] now you can see that we have three circles and they intersect at one place and that place in this example would be matangas therefore if the point of intersection in this demonstration is batangas it will be the epicenter of the earthquake [Music] so that's all for this demonstration thank you for watching