San Francisco's big 1906 quake was third of a series on San Andreas Fault

Research led by a University of Oregon doctoral student in California's Santa Cruz Mountains has uncovered geologic evidence that supports historical narratives for two earthquakes in the 68 years prior to San Francisco's devastating 1906 disaster.

The evidence places the two earthquakes, in 1838 and 1890, on the San Andreas Fault, as theorized by many researchers based on written accounts about damage to Spanish-built missions in the Monterey and San Francisco bay areas. These two quakes, as in 1906, were surface-rupturing events, the researchers concluded.

Continuing work, says San Francisco Bay-area native Ashley R. Streig, will dig deeper into the region's geological record -- layers of sediment along the fault -- to determine if the ensuing seismically quiet years make up a normal pattern -- or not -- of quake frequency along the fault.

Streig is lead author of the study, published in this month's issue of the Bulletin of the Seismological Society of America. She collaborated on the project with her doctoral adviser Ray Weldon, professor of the UO's Department of Geological Sciences, and Timothy E. Dawson of the Menlo Park office of the California Geological Survey.

The study was the first to fully map the active fault trace in the Santa Cruz Mountains using a combination of on-the-ground observations and airborne Light Detection and Ranging (LiDAR), a remote sensing technology. The Santa Cruz Mountains run for about 39 miles from south of San Francisco to near San Juan Batista. Hazel Dell is east of Santa Cruz and north of Watsonville.

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Experimental Storm-Surge Maps to Accompany NOAA Hurricane Projections

Emergency management crews will have another tool to help them protect low-lying areas from flooding the next time a hurricane approaches.

Beginning this year, the National Hurricane Center's projections will include surge maps that show where flooding is expected along the Gulf and Atlantic coasts.

Flooding that usually accompanies a hurricane is caused by a storm surge -- a rise in ocean water caused by the atmospheric pressure and wind that pushes water landward. Storm surges can kill, with nine out of every 10 deaths from hurricanes caused by the surge or its flooding, according to Federal Emergency Management Agency statistics.

The surge maps, which will be experimental for at least two years, will be issued at the first sign of a hurricane or tropical storm watch and will be continuously updated with each new hurricane forecast, typically issued every six hours, according to a release from hurricane center's parent agency, the National Oceanic and Atmospheric Administration.

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