HR: 17:45h
AN: S54A-08    [Abstracts]
TI: Finite-Source Modeling of Micro-earthquakes on the Parkfield Segment of the San Andreas Fault
AU: * Dreger, D
EM: dreger@seismo.berkeley.edu
AF: Berkeley Seismological Laboratory, 215 McCone Hall University of California, Berkeley, CA 94720, United States
AU: Morrish, A
EM: amorrish@seismo.berkeley.edu
AF: Berkeley Seismological Laboratory, 215 McCone Hall University of California, Berkeley, CA 94720, United States
AU: Nadeau, R
EM: nadeau@seismo.berkeley.edu
AF: Berkeley Seismological Laboratory, 215 McCone Hall University of California, Berkeley, CA 94720, United States
AB: We have investigated the rupture kinematics of the SAFOD target repeating events by inverting seismic moment rate functions obtained from empirical Green's function deconvolution using the Berkeley Seismological Laboratory High Resolution borehole Seismic Network (HRSN). With this method it is assumed that if a suitable empirical Green's function (eGf) can be found, namely a collocated smaller event with the same radiation pattern as the targeted larger event, the shared propagation, attenuation and site effects can be removed by deconvolution of the smaller signal from the larger one leaving the moment rate function of the target event. The obtained moment rate functions are then inverted for the spatial distribution of moment release, the rupture speed and possibly the slip velocity. In this study we present inversions for the Mw2.1 "San Francisco" and the Mw1.8 "Hawaii" repeating sequences using nearly collocated (order of 10m) M<1.0 events as the eGfs. The deconvolution process recovers stable seismic moment rate functions with excellent signal to noise ratios. The functions display azimuthal variability which may be due to directivity. Our results indicate that the small repeating events are kinematically similar to larger earthquakes in terms of slip-pulse behavior, rupture velocity and slip velocity. However, we find that rupture area is extremely compact (radius of 20m), with large peak slip. Stress drops estimated from the finite-source slip models are correspondingly high, with average and peak stress drops for the 5 studied "San Francisco" sequence events ranging from 8.3-14.5MPa, and 65.0-93.8MPa, respectively. Thus the finite-source modeling is consistent with both the relatively low estimates of average stress drop reported from studies using spectral corner frequency methods (e.g. Imanishi et al., 2004) as well as the high estimates inferred from the tectonic loading asperity model of Nadeau and Johnson (1998). The results indicate that substantial stress and strength heterogeneity exists along the San Andreas fault.
DE: 7209 Earthquake dynamics (1242)
DE: 7215 Earthquake source observations (1240)
SC: Seismology [S]
MN: 2007 Fall Meeting