Earthquakes By Mr. D and some slides taken from the USGS

Earthquakes usually occur on faults caused by the subduction of two plates

Lisa WaldUSGS Pasadena

U.S. Department of the InteriorU.S. Geological Survey

USGS Earthquake Hazards Program

Plate Tectonics

Plate Boundaries

Three Types of Faults

Strike-SlipThrust

Normal

Strike-slip Fault Example

Normal Fault Example

Dixie Valley-Fairview Peaks, Nevada earthquakeDecember 16, 1954

Thrust Fault Example

Thrust Fault Example

Bigger Faults Make Bigger EarthquakesBigger Faults Make Bigger Earthquakes

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5.5 6 6.5 7 7.5Magnitude

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Bigger Earthquakes Last a Longer TimeBigger Earthquakes Last a Longer Time

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5.5 6 6.5 7 7.5 8

Magnitude

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What Controls the Level of Shaking?What Controls the Level of Shaking?

• Magnitude– More energy released

• Distance– Shaking decays with distance

• Local soils– amplify the shaking

Is there such a thing as “Earthquake Weather”???

Earthquake Effects - Ground Shaking

Northridge, CA 1994

Earthquake Effects - Ground Shaking

KGO-TV News ABC-7

Loma Prieta, CA 1989

Earthquake Effects - Surface Faulting

Landers, CA 1992

Earthquake Effects - Landslides

Turnagain Heights, Alaska,1964 (upper left inset);Santa Cruz Mtns, California , 1989

Source: National Geophysical Data Center

Earthquake Effects - Fires

KGO-TV News ABC-7

Loma Prieta, CA 1989

Earthquake Effects - Tsunamis

Photograph Credit: Henry Helbush. Source: National Geophysical Data Center

2011 Tsunami in Japan

Seismic Waves

Richter magnitude scale

• One way we measure magnitude.

• Developed in 1935 by Charles Richter in partnership with Beno Gutenberg, both of the California Institute of Technology.

• An earthquake that measures 5.0 on the Richter scale has a shaking amplitude 10 times larger than one that measures 4.0.

Earthquake Magnitude

Earthquake Magnitude ScaleMagnitude Earthquake Effects Estimated

• 2.5 or less: Usually not felt, but can be recorded by seismograph (frequently occurs in CA).

• 2.5 to 5.4: Often felt, but only causes minor damage. • 5.5 to 6.0: Slight damage to buildings and other structures.• 6.1 to 6.9May cause a lot of damage in very populated

areas.• 7.0 to 7.9: Major earthquake. Serious damage.20• 8.0 or greater: Great earthquake. Can totally destroy

communities near the epicenter.

EPICENTER

• the point on the Earth's surface that is directly above the hypocenter or focus, the point where an earthquake or underground explosion originates.

Earthquake Location

The San Andreas Fault

Pacific-North American Plate Boundary

Will California eventually fall into the ocean???

Why not?

• The motion between the pacific and the north American plates beneath us is mostly horizontal. That is, the Pacific plate is moving "up" the coast, not away from the North American plate, at a rate of dozens of millimeters per year.

• So in several million years, residents of San Francisco will see the L.A. skyline out their windows.

Faultsof SouthernCalifornia

Source: SCEC Data Center

Shaking Hazard in Southern California

Real-time Earthquake Information

Any Questions?

• Remember you will have a test on this- so ask the questions now before you forget.