HR: 1340h
AN: S53A-1086    [Abstracts]
TI: The 2004 Parkfield Earthquake and its Relation to the Surrounding Fault-Zone Structure
AU: * Custodio, S
EM: susana@crustal.ucsb.edu
AF: Department of Earth Science, University of California, Santa Barbara, Santa Barbara, CA 93106 United States
AU: * Custodio, S
EM: susana@crustal.ucsb.edu
AF: Institute for Crustal Studies, University of California, Santa Barbara, Santa Barbara, CA 93106-1100 United States
AU: Liu, P
EM: pcliu@crustal.ucsb.edu
AF: Institute for Crustal Studies, University of California, Santa Barbara, Santa Barbara, CA 93106-1100 United States
AU: Archuleta, R J
EM: ralph@crustal.ucsb.edu
AF: Department of Earth Science, University of California, Santa Barbara, Santa Barbara, CA 93106 United States
AU: Archuleta, R J
EM: ralph@crustal.ucsb.edu
AF: Institute for Crustal Studies, University of California, Santa Barbara, Santa Barbara, CA 93106-1100 United States
AB: The Parkfield section of the San Andreas Fault, California, is one of the best-studied fault zones in the world. Velocity structure studies (Michelini and McEvilly, 1991; Eberhart-Phillips and Michael, 1993; Thurber et al., 2003), magneto-telluric work (Unsworth and Bedrosian, 2004), and recent drilling at SAFOD show that the rock material in the Parkfield region is extremely heterogeneous. In terms of seismic activity, Parkfield is characterized by repetitive microseismicity - small earthquakes repeat in the same locations with well-defined recurrence intervals. Also larger earthquakes, Mw6, take place in Parkfield. Bakun and McEvilly (1984) proposed that Mw6 Parkfield characteristic earthquakes would repeat every 22 years, nucleate at a common hypocenter, and always rupture the same fault area, releasing the same amount of energy. However, the 2004 Mw6 Parkfield earthquake happened 39 years after the previous Mw6 earthquake, nucleated approximately 20 km SE of previous events, and ruptured from SE to NW, unlike the previous Mw6 earthquakes. The 2004 event generated the largest ground-motion ever observed for a Mw6 earthquake. We use data from the 1983 Coalinga earthquake to infer site effects in the Parkfield region. We conclude that most stations in the fault zone are strongly affected by local amplifications and resonance. In particular, most the large Peak Ground Velocities (PGVs) can be explained by site conditions. This observation is in agreement with fault-zone studies that evidence extreme material heterogeneity at Parkfield. We obtain a kinematic model for the 2004 Mw6 earthquake from the inversion of near-source strong-motion seismic data. We correct the data in order to take in account site effects as observed for the Coalinga earthquake. The inversion yields a non-unique solution - we compute several acceptable rupture models and observe which features are robust. We relate the robust slip features to relocated microseismicity (both before and after the mainshock), to the largest aftershocks (4w<5), and to material structure around the fault zone (inferred from tomography and SAFOD drilling).
DE: 3260 Inverse theory
DE: 7215 Earthquake source observations (1240)
DE: 7223 Earthquake interaction, forecasting, and prediction (1217, 1242)
DE: 8118 Dynamics and mechanics of faulting (8004)
SC: Seismology [S]
MN: Fall Meeting 2005