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New USGS Maps Show San Francisco Bay Area's Active Faults and Underlying Geologic Deposits
Released: 4/20/2006 1:39:11 PM

Contact Information:
U.S. Department of the Interior, U.S. Geological Survey
Office of Communication
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Reston, VA 20192
Stephanie Hanna 1-click interview
Phone: (206) 331-0335

Scott Harris 1-click interview
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The U.S. Geological Survey (USGS) is releasing two new maps providing a new look at the hazards and geologic history of the greater San Francisco Bay Area.

The first map/poster updates the locations of all faults in the Bay Area known to have deformed the Earth´s surface during the past 2 million years using the latest, most detailed digital mapping. The most hazardous faults include those that broke during historic earthquakes in 1868, 1906, and 1989, along the San Andreas and Hayward faults.

According to Russ Graymer, the USGS geologist who led the project, "several other hazardous faults include the Rodgers Creek, Calaveras, San Gregorio, Greenville, and Green Valley Faults." Graymer notes that "there is evidence that these faults produced large earthquakes within the past few hundred years."

The new printable and digital map/poster compiles the latest and best known locations for these faults, and for all faults known to have generated earthquakes in the past 2 million years.

The second map/poster shows the Bay Area´s geologic materials and structures, which is in part derived from the new map of young (Quaternary) geologic deposits announced by the USGS last February. This poster reveals the complicated geologic history that has led to the landscape that shapes the Bay Area. This new USGS poster is unique in the United States for its level of detail and scope of coverage for a major urban area.

These new products are the most accurate and detailed depiction of active faults, geologic materials, and geologic structures of the region ever produced. They will be invaluable in assessing ground water and other geologic resources, ecological habitats, as well as hazards including seismic amplification, liquefaction, ground rupture hazard, and landslides. Given the region´s recent record rainfalls and threat of landslides, these maps are particularly timely.

"These maps are in invaluable resource for our ongoing project of mapping earthquake-induced landslide hazard throughout the San Francisco Bay region," said David Keefer, a USGS landslide expert. "They make possible application of a new model for this mapping, which returns probabilistic outputs of hazard levels for the very different types of landslides that are triggered by earthquakes.

"Together these map/posters illustrate how earthquakes and the faults that cause them have shaped the region since the time of the dinosaurs," said Graymer. "The hills around the Bay Area may look like they have been there forever, but they are actually recent geologically, pushed up by the same forces that cause earthquakes. The rock under your house may have originated hundreds, even thousands of miles away. The Earth is amazingly dynamic."

A web site accompanying these publications allow the public to click on the maps, and be taken to additional geologic stories, field trips, photographs, and other images, as well as to download the maps. Users can also explore the relationship between the landscape and the underlying geology. These can be found on the web at http://sfgeo.wr.usgs.gov.

"These posters will be valuable to educators as the basis for effective interactive learning experiences for students at many grade levels," said David Anderson, Professor of Geology at San Jose State University. These posters are intended primarily for informational and educational purposes. The official state Alquist-Priolo Earthquake Fault Zones maps that govern construction setbacks and disclosure are produced by the California Geological Survey (CGS).

"These map products incorporate many years of dedicated work by the USGS, CGS, and others, and are an invaluable source of geological information for Californians," said John Parrish, California State Geologist. "It is through these types of cooperative mapping programs between Federal and State agencies that California´s communities and businesses receive the greatest benefits. CGS is very pleased to have been a part of the team that contributed to the creation of these posters."

"The great thing about these maps is that they provide a complete digital picture of the major faults of the Bay Area, including detailed fault mapping by the California Geological Survey for establishing Alquist-Priolo Earthquake Fault Zones, and more recent detailed mapping by the USGS and others," said Chris Wills, a supervising geologist with CGS. "They will help identify areas that may need re-evaluation of the Alquist-Priolo Earthquake Fault zones and will form a consistent baseline for any evaluations of the Bay Area´s faults."

To learn more about fault-related regulatory maps produced by the California Geological Survey, see http://gmw.consrv.ca.gov/shmp/. Interactive versions of CGS Alquist-Priolo Earthquake Fault Zone Maps are available online at http://quake.abag.ca.gov/faults/.

Additional collaborators are from several consulting firms including William Lettis & Associates, Sanders & Associates Geotechnical Engineering, Lachel Felice & Associates, and Tierra Geosciences.

Both new resources are available free online: http://pubs.usgs.gov/sim/2006/2919 and http://pubs.usgs.gov/sim/2006/2918. For a complete list of 1906 Centennial Alliance Events, exhibits, lectures, and publications, see http://1906centennial.org/activities/. For other 1906 related information released by the USGS see http://earthquake.usgs.gov/1906/.


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