Environmental Geology lecture outline - Events associated with earthquakes and some case histories.

What happens during an earthquake that is of potential concern?

Interplate earthquake case histories (so many!).

Kobe, Japan, January 17, 1995, case history.

San Fernando Valley Earthquakes: Feb. 9, 1971 and Jan 17, 1994

Intraplate earthquake case histories:

New Madrid, Missouri:

Charleston, South Carolina August, 31st 1886:

Nebraska and the Humboldt fault zone?

Common traits of intraplate earthquakes? They are associated with old buried fault zones that are part of continental rifts and they have lower slip rates and longer recurrence intervals than interplate earthquakes.

Induced sesimicity case histories

1960s, Rocky Mountain Arsenal in Colorado:

Rangely anticline, CO and S-central NE, secondary recovery of oil by injection of fluids, increasing pore pressure and flushing oil from reservoir.

Koyna Dam near Bombay, India;

Lake Mead another example.

Fluid injection (or withdrawal) and reservoir infilling can induce earthquakes.

The orange colored gravity anomaly depicted on the image below is a representation of an old buried feature, the Keweenawan rift. The rift contains basaltic rocks, which are denser than the surrounding rocks and hence cause a positive gravity anomaly feature. The Humboldt fault zone in the SE corner of Nebraska likely represents present-day seismic reactivation of this older feature.

H.D. Maher Jr., 3/2/98

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