Topic: What Causes Earthquakes? PSSA: A / S8.D.1.1

Objective:  TLW explain where earthquakes take place.  TLW describe the types of faults associated with plate boundaries.  TLW compare the three types of waves that are generated by earthquakes.

MI #1: Seismology  An earthquake is a movement or trembling of the ground caused by a sudden release of energy when rocks move along a fault.  Seismology is the study of earthquakes.

MI #2: Where do earthquakes occur?  Most earthquakes occur along tectonic plate boundaries.  Faults, or breaks in the Earth’s crust, happen along these boundaries.

MI #3: What causes earthquakes?  Deformation is primarily responsible for causing earthquakes.  Plastic deformation is like molded clay and does not cause earthquakes.  Elastic deformation occurs when rock under stress is stretched without breaking (like a rubber band).  Elastic rebound occurs when elastically deformed rock snaps back to its original shape.

MI #4: Faults at Plate Boundaries  Transform Boundary = Strike-slip fault  Convergent Boundary = Reverse Fault  Divergent Boundary = Normal Fault

MI #5: Seismic Waves  Seismic waves are waves of energy that travel through the earth away from an earthquake in all directions.  Body waves travel through the Earth’s interior, while surface waves travel along Earth’s surface.

MI #6: Types of Seismic Waves  P waves: aka Primary waves, compressional, fastest earthquake waves  S waves: aka Secondary waves, side to side motion, second fastest  Surface waves: move like water waves, slowest, most destructive

So What…? Real Life Application  Understanding earthquake waves is important to understanding how earthquake epicenters are located.