HR: 09:45h
AN: S41B-08    [Abstracts]
TI: Site Response in the Northern San Francisco Bay, California
AU: * Bergen, K
EM: kristian.bergen@gmail.com
AF: U.S. Geological Survey, 345 Middlefield Rd. MS 977, Menlo Parkq, CA 94025, United States
AU: Fletcher, J
EM: jfletcher
AF: U.S. Geological Survey, 345 Middlefield Rd. MS 977, Menlo Parkq, CA 94025, United States
AU: Boatwright, J
EM: boat@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd. MS 977, Menlo Parkq, CA 94025, United States
AU: Sell, R
EM: sell@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd. MS 977, Menlo Parkq, CA 94025, United States
AU: Detweiler, S
EM: shane@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd. MS 977, Menlo Parkq, CA 94025, United States
AU: Noce, T
EM: noce@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd. MS 977, Menlo Parkq, CA 94025, United States
AU: Holzer, T
EM: tholzer@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd. MS 977, Menlo Parkq, CA 94025, United States
AB: Santa Rosa, California sustained unexpectedly high damage from the 1906 San Francisco earthquake (M7.8) and the 1969 Santa Rosa Earthquake sequence (M5.6 and M5.7). At the nearby city of Napa, ground motion was also unexpectedly high during the 2000 Yountville earthquake (M5.2). This history of unexpectedly strong ground motion, in combination with high metropolitan populations in Santa Rosa (over 450,000) and Napa (over 100,000), and their close proximities to Holocene active faults such as the Rodgers-Healdsburg fault system, West Napa Fault, and Green Valley fault, make estimation of site response in these regions particularly important. We estimate site response at 24 sites in this region by inverting seismograms of local events (radius < 100km) for source, site, and propagation characteristics. Regional seismicity was recorded from January, 2004, to September, 2006. We inverted spectra of 33 earthquakes for P-waves and 25 earthquakes for S-waves, covering a range of hypocentral distances and azimuths. Seismic cone penetration testing (SCPT) was done at three stations in Santa Rosa and three stations in Napa to determine near surface S-wave velocities and constrain absolute site amplification. High site response is estimated from the inversion in the city of Napa, in agreement with slower near-surface S-wave velocities from SCPT. Response is estimated to be lower at adjacent sites outside of the valley. Site response is also high in the city of Santa Rosa, although lower than Napa. High response in Santa Rosa is in agreement with faster near-surface S-wave velocities from SCPT.
DE: 7203 Body waves
DE: 7205 Continental crust (1219)
DE: 7255 Surface waves and free oscillations
DE: 7290 Computational seismology
DE: 7294 Seismic instruments and networks (0935, 3025)
SC: Seismology [S]
MN: 2007 Joint Assembly