Earthquakes By Mr D and some slides taken

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

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

Plate Tectonics USGS Earthquake Hazards Program Lisa Wald USGS Pasadena U. S. Department of the Interior U. S. Geological Survey

Plate Boundaries

Three Types of Faults Strike-Slip Thrust Normal

Strike-slip Fault Example

Normal Fault Example Dixie Valley-Fairview Peaks, Nevada earthquake December 16, 1954

Thrust Fault Example

Bigger Faults Make Bigger Earthquakes

Bigger Earthquakes Last a Longer Time

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 Loma Prieta, CA 1989 KGO-TV News ABC-7

Earthquake Effects - Surface Faulting Landers, CA 1992

Earthquake Effects - Landslides Source: National Geophysical Data Center Turnagain Heights, Alaska, 1964 (upper left inset); Santa Cruz Mtns, California , 1989

Earthquake Effects - Fires Loma Prieta, CA 1989 KGO-TV News ABC-7

Earthquake Effects - Tsunamis 2011 Tsunami in Japan Photograph Credit: Henry Helbush. Source: National Geophysical Data Center

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 Scale Magnitude 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. 9 May 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.