HR: 08:30h
AN: S31C-03    [Abstracts]
TI: Vibroseis Monitoring of San Andreas Fault in California: What Can Be Done Next.
AU: * Korneev, V
EM: vakorneev@lbl.gov
AF: Lawrence Berkeley National Laboratory, 1 Cyclotron Rd, Berkeley, CA 94720
AU: Nadeau, R
EM: nadeau@seismo.berkeley.edu
AF: UC Berkeley, UCB, Seismological station, Berkeley, CA 94720
AB: In the Vibroseis monitoring experiment, seismic waves repeatedly illuminated the epicentral region of the expected M6 event San Andreas Fault (SAF) at Parkfield from June 1987 until November 1996. For this effort, a large shear-wave vibrator was interfaced with the 3-component (3-C) borehole High-Resolution Seismic Network (HRSN), providing precisely timed collection of data for detailed studies of changes in wave propagation associated with stress and strain accumulation in the fault zone (FZ). The investigations reported significant traveltime changes in the S coda for paths crossing the fault zone southeast of the epicenter and above the rupture zone of the 1966 M6 earthquake. Analysis and modeling of these data and comparison with observed changes in creep, water level, microseismicity, slip-at-depth and propagation from characteristic repeating microearthquakes showed temporal variations in a variety of wave propagation attributes that were synchronous with changes in deformation and local seismicity patterns. Numerical modeling suggests 200 meters as an effective thickness of SAF. The observed variations can be explained by velocity 6% velocity variation within SAF core. Guided wave amplitude tomographic inversion for SAF using microearthquakes, shows clearly that FZGW are significantly less attenuated in a well-defined region of the FZ. This region plunges to the northwest along the northwest boundary of the region of highest moment release and separates locked and slipping sections of the SAF at depth, as determined independently from geodesy, seismicity and the recurrence rates of characteristically repeating microearthquakes. Temporal changes of FZGW correlates with changes in overall seismicity. Active monitoring of changes in FZGW has a potential for imaging and detecting of changes in strees within FZ cores.
DE: 7223 Seismic hazard assessment and prediction
DE: 7230 Seismicity and seismotectonics
DE: 7260 Theory and modeling
DE: 5144 Wave attenuation
DE: 7209 Earthquake dynamics and mechanics
SC: Seismology [S]
MN: 2004 AGU Fall Meeting