Lecture 16

# Lecture 16 - GEOS 1004 SPOTILA/27/09 Earthquakes What is an...

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GEOS 1004, SPOTILA Lecture 16, 10/27/09 Earthquakes What is an earthquake? -release of elastic energy (seismic waves, shaking) caused by motion along a fault -fault motion causes the earthquake; the earthquake does not cause or produce the fault. Earthquakes are an effect. Are earthquakes produced as single points, like epicenters? No, they occur on plate boundaries and are planar actions possibly 1000s of km long *Fault ruptures can be very long; 1857 San Andreas fault M8 = 300 km 1964 Alaska, M9.2 = 800 km -seismic energy is released all during the rupture, as the rupture propagates from one end to the other. Where do earthquakes occur? Plate Boundaries Rare events occur within plates; 1886, M6.7 Charleston, SC 1812, M8.2 New Madrid, MO Earthquakes are produced by stick-slip fault motion. -occur in brittle deformation; stress causes rocks to “strain” (deform) elastically -elastic strain = recoverable, like a spring -plate motion causes rocks to strain (deform) elastically -this occurs until the rock strength is exceeded, and then snap -sudden motion, releases seismic waves. =Elastic Rebound Theory Loading and release of elastic strain is systematic; a fault will have a certain “rate”. So can we predict earthquakes?

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Lecture 16 - GEOS 1004 SPOTILA/27/09 Earthquakes What is an...

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