California forecast earthquake may be more powerful than originally estimated
FEWW Moderators have upgraded their forecast for a California earthquake to a Magnitude 7.9 event.
For initial forecast see California Earthquake Forecast 2009 [March 24, 2009]
For Update # 1 see: California Earthquake Forecast 2009 – UPDATE [August 4, 2009]
San Andreas Fault
The topographic texture of western California is controlled by the San Andreas fault system, the tectonic expression of the Pacific plate sliding northwestward along the western margin of the North American plate. Hundreds of miles long and up to a mile wide, the San Andreas Fault Zone has been active since its original development in the Tertiary. About 10 percent of the present plate motion is compressional, which means horizontal forces are shortening and wrinkling the crust along the fault zone. This movement has created the parallel coastal northwest-southeast mountain ranges such as the Coastal Ranges along California’s central coast. Comparatively quiet during the period between the 1906 San Francisco earthquake and the 1989 Loma Prieta event, the fault is again showing activity. Image and caption: nationalatlas.gov
Fault map for San Francisco Bay Area from http://www.abag.ca.gov/bayarea/eqmaps/pickcity.html, annotated and colors modified by User: Leonard G. Released into the public domain (Leonard G. ).
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