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Rupture Process of the 2004 Parkfield Earthquake Utilizing Near-Fault Seismic Records and Implications for Shakemap

by Douglas Dreger and Ahyi Kim

Dreger, Douglas and Ahyi Kim (2006). Rupture Process of the 2004 Parkfield Earthquake Utilizing Near-Fault Seismic Records and Implications for ShakeMap. SMIP06 Seminar on Utilization of Strong-Motion Data, p. 1 - 18.

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Abstract

The September 28, 2004 Parkfield earthquake, arguably the best recorded earthquake ever, allows for detailed investigation of finite-source models, and their resolution. We have developed models using GPS and InSAR geodetic data, and CSMIP and USGS strong motion seismic waveforms independently and jointly. In order to focus on better resolved long wavelength features the seismic data was lowpass filtered at 0.5 Hz. We have investigated the sensitivity of the finite-source models due to station coverage, weighting and smoothing parameters, and seismic velocity structure. The resulting model is consistent with preliminary results using regional broadband and strong motion waveform data (e.g. Langbein et al., 2005; Dreger et al., 2005) as well as with higher frequency seismic waveform only inversions (e.g. Custódio et al., 2005; Liu et al., 2006). The scalar seismic moment was found to be 1.28e25 dyne cm (Mw6.0), the overall rupture length 25 km, the peak slip 58 cm, and the average rupture velocity 2.6 km/s. The rupture was predominantly unilateral to the NW with a small component to the SE. The obtained slip model was used to simulate 3D wave propagation taking into account the velocity contrast across the San Andreas Fault, and a narrow low-velocity fault zone. The results of this analysis suggest observed waveform complexity and amplitudes at stations located in the fault zone could be due to fault zone guided waves.