Earthquakes

Earthquakes - Stress - force exerted per unit area within...

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Subject: Environmental Geology Case History - Northridge Quake quake struck LA - Jan 17, 1994 • initiated on a steep fault surface ~18 km (11 mi) below surface • shaking lasted about 15 seconds • killed 57 people, collapsed freeways, parking structures, 3000+ buildings • $40 billion property damage Earthquakes violent ground-shaking phenomenon by sudden release of strain energy stored in rocks • globally, most earthquakes are concentrated along lithospheric plate boundaries • USGS estimates about 1 million quakes annually • millions of people killed and billions of dollars in damage have been due to catastrophic earthquakes • 2010 Haiti 7.0 - 230,000 killed, 1.5 million homeless Causes for Earthquakes Stress and strain in rocks
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Unformatted text preview: Stress - force exerted per unit area within rocks on other Earth materials Strain - deformation (size, shape, orientation) on rock materials caused by stress Rock strength - rock's ability to withstand a magnitude level of stress before rupture Earthquake - sudden release of strain energy caused by rock rupture (through faulting) some earthquakes induced by human activities - smaller magnitude, reservoir-induced earthquakes, deep waste disposal cause slippage/earthquakes, nuclear explosions Earthquake has a focus on a fault - surface level focus = epicenter, fault = fault scarp Earthquake Magnitude Scale Richter scale: amplitude of seismic wave indication ground motion. Log Scale increase of one order in magnitude = tenfold increase in magnitude Moment Magnitude scale: amount of strain energy released...
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This note was uploaded on 11/19/2011 for the course GEOL 1011 taught by Professor Brown during the Fall '11 term at GWU.

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Earthquakes - Stress - force exerted per unit area within...

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