Causes of Earthquakes Lecture Notes

Primary Causes of Earthquakes

1. Plate Boundary Interactions
   • Learned about in the previous plate tectonics unit.
2. Volcanic Eruptions
   • Magma rising to the surface exerts pressure, causing surrounding rocks to crack and shift.
3. Nuclear Detonation
   • Example: Castle Bravo test
     • Largest U.S. nuclear detonation on March 1, 1954, at Bikini Atoll.
     • Expected yield: 4-8 megatons; Actual yield: 15 megatons.
     • 1,000 times more powerful than Hiroshima.
     • Mushroom cloud reached 25 miles high and 25 miles diameter in under 10 minutes.
     • Created a 6,500 feet wide and 250 feet deep ocean floor crater.
     • Vaporized two islands and part of a third.
4. Meteor Impact
   • Reference: Chicxulub impact crater in Yucatan Peninsula, learned in astronomy unit.
   • Asteroid: 6 miles wide, traveling at ~45,000 mph.
   • Released energy 10,000 times greater than all nuclear weapons combined.
   • Created a crater ~125 miles wide.
   • Fractures surrounding rock and creates faults.
5. Dams/Mining/Fracking
   • Discussed in the reading assignment "How Humans are causing Earthquakes."

U.S. Earthquake Hazard Maps Analysis (2008-2023)

• Key Questions:
  1. Where are the highest hazards in the US?
  2. What is the risk level in Massachusetts?
  3. What new places have increased in risk over the last 15 years?
  4. Why have risks/hazards increased?

Hydraulic Fracturing - Fracking

• Discussed as a human-induced cause of earthquakes.

Historical Earthquakes

• Cape Ann Earthquake of 1755
  • Magnitude: 6.0-6.3
  • Largest earthquake in colonized Boston history.
  • Occurred despite not being on a plate boundary.

Faults

• Bloody Bluff Fault
  • Located between Concord and Lexington in Minute Man National Historical Park.
  • Named after a revolutionary skirmish.
  • Nashoba: referred to as "hill that shakes."