Earthquakes

(1) What causes earthquakes? It’s plate movement Movement in the crust causes stress– energy that slowly changes the shape of rock Earthquake– shaking from the sudden movement of rock at a fault (stress is quickly released) Bedarliex, France Bedarliex, France

Fault energy can be released all at once and cause elastic rebound

(2) Where do earthquakes occur? Pacific PlateN.A. Plate

(2) Where do earthquakes occur? 1) At strike-slip faults, plates move at sliding boundaries (San Andreas Fault, CA)  Pacific PlateN.A. Plate

(2) Where do earthquakes occur? 1) At strike-slip faults, plates move at sliding boundaries (San Andreas Fault, CA) 2) Large earthquakes can occur at subduction zones, colliding boundaries (near Japan)  N. A. Plate Pacific Plate

Where do earthquakes occur? 1) At strike-slip faults, plates move at sliding boundaries (San Andreas Fault, CA) 2) Large earthquakes can occur at subduction zones, colliding boundaries (near Japan or Chile) 3) Smaller ‘quakes happen at mid-ocean ridges & rift zones, spreading boundaries (Mid-Atlantic Ridge)  N. A. Plate Eurasian Plate

Epicenter & Focus epicenter- point on Earth’s surface directly above the focus focus- area beneath the surface, where the release of fault energy starts an earthquake

(4) What are seismic waves? seismic waves- vibrations made from the release of an earthquake’s energy These waves travel outward from the focus…

(4) What are seismic waves? seismic waves- vibrations made from the release of an earthquake’s energy These waves travel outward from the focus… …underground through Earth’s body of solid rock (P waves or S waves)

(4) What are seismic waves? seismic waves- vibrations made from the release of an earthquake’s energy These waves travel outward from the focus… …underground through Earth’s body of solid rock (P waves or S waves) …and above ground as destructive surface waves (L waves, long-waves)

(5) How do waves move underground? First, there are… - Primary or pressure waves are the fastest, and cause rock to compress & expand (push-pull) P waves- Primary or pressure waves are the fastest, and cause rock to compress & expand (push-pull)

(6) Next, are underground… S waves- secondary or shear waves; travel slower than primary waves, up-and-down (back and forth)

(7) S waves can move through solids (rock), but NOT through liquids or gases What happens to the S waves (blue)?

(8) How do surface waves move? P and S waves above the ground… …are L waves, called surface waves- the slowest waves; slower than P & S waves

(8) How do surface waves move? P and S waves above the ground… …are L waves, called surface waves- the slowest waves; slower than P & S waves …cause severe shearing of the ground (side-to-side) …can make the ground roll like waves on water

gory/japan/ gory/japan/ gory/japan/ gory/japan/ Penn. State Univ. ML/Classes/IntroQuakes/Notes/waves_an d_interior.html Penn. State Univ. ML/Classes/IntroQuakes/Notes/waves_an d_interior.html ML/Classes/IntroQuakes/Notes/waves_an d_interior.html ML/Classes/IntroQuakes/Notes/waves_an d_interior.html Wikipedia Wikipedia

Where do earthquakes occur? 1) At strike-slip faults, plate move at sliding boundaries (San Andreas Fault, CA) 2) Large earthquakes can occur at subduction zones, colliding boundaries (near Japan or Chile) 3) Smaller ‘quakes happen at mid-ocean ridges, spreading boundaries (Mid-Atlantic Ridge) Nazca Plate S. A. Plate

How does a magnitude 6 compare to a 5 ? The waves are 10 times greater from a magnitude 6 than those from a magnitude 5 earthquake A magnitude 6 releases about 30 times more energy than a magnitude 5 Richter Magnitude Strength (amplitude) Energy Released 5XY 610X30Y 7100X1000Y