Faults and Earthquakes. Some faults become “locked” –Pressure pushes together the irregular walls of the fault; surfaces resist sliding Slip can’t occur.

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Presentation transcript:

Faults and Earthquakes

Some faults become “locked” –Pressure pushes together the irregular walls of the fault; surfaces resist sliding Slip can’t occur until enough stress is built up to overcome resistance

Earthquake ! Focus - point of initial rupture Epicenter - point on surface directly above the focus

The energy released by the earthquake increases with (a) the area of the fault plane that slips (b) the slip distance (c) the strength of the rocks It’s easy to break contact points on a small section of fault, that allows a little slip. Large slip on big sections of a fault, requires an rare alignment of contacts points. therefore larger earthquakes are rarer than small earthquakes.

Earthquake Damage - ground displacement

Earthquake Damage - shaking

San Francisco, 1906 Earthquake Damage - fire

Measurement of Earthquake Magnitude, continued –M 5 earthquake versus M 7 earthquake M 7 has 100X stronger shaking, ~900X the energy Magnitude is measured on a Logarithmic Scale An increase in 1 whole number represents an earthquake that has 10 times stronger ground motion ~30 times as much energy release

Sources of Earthquake Damage shaking liquifaction- shaking can cause water-saturated soil to behave like a fluid: buildings sink or tip over fire tsunami landslides ground displacement

Dangerous factors contributing to earthquake deaths Dense populations Building style Time of day Relief infrastructure

Earthquake Hazard

California Earthquakes 1989 Loma Prieta Hector Mine Landers Northridge San Fernando Long Beach Kern County Owens Valley Fort Tejon Coalinga San Francisco 7.9

Tsunami (incorrectly called “tidal wave”) Open sea Wave height: cm to 1 m Speed: 750 km/hr Near shore Wave height: up to tens of meters Seismically-induced sea wave

2004 Indian Ocean Tsunami

2004 Sumatra “Tsunami” Earthquake Dec. 26, 2004 : M 9.0 earthquake (4th largest recorded) occurs off northern Sumatra; ~500 km section of fault moves, with max. of 20 m of slip

Several meters of seafloor movement triggers tsunami Wave height on Sumatra - 30 m Thailand - 10 m Sri Lanka - 15 m India - 5 m