HR: 17:15h
AN: S54A-06    [Abstracts]
TI: Multiscale slip inversion analysis of the 2004 Parkfield earthquake
AU: * Uchide, T
EM: uchide@eps.s.u-tokyo.ac.jp
AF: EPS, the Univ. of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan
AU: Ide, S
EM: ide@eps.s.u-tokyo.ac.jp
AF: EPS, the Univ. of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan
AU: Beroza, G
EM: beroza@pangea.stanford.edu
AF: Stanford Univ., 397 Panama Mall, Stanford, CA 94305-2215, United States
AB: The question of how small ruptures grow into to large earthquakes is fundamental to earthquake seismology. In particular, the question of whether or not the initiation of small earthquakes differs from the initiation of large earthquakes is important for understanding whether or not earthquakes are predictable, and also for developing methods for earthquake early warning. As a case study, we analyze the 2004 Parkfield earthquake using the multiscale slip inversion method [ Uchide and Ide, JGR, 2007] with a multiscale fault model composed of three fault planes of different size, 4.0 × 4.0, 8.0 × 8.0, and 30.0 × 14.0 km². The advantage of the multiscale approach is that it allows us to analyze the initiation of the earthquake in detail, while still analyzing the entire event at a coarser scale. For the analysis at the smaller two scales, we use velocity seismograms of small events (M_W 2.3 - 3.7) as empirical Green's functions to invert the initial part of mainshock accelerograms. All data are from GEOS (General Earthquake Observation System) developed by the USGS. In the frequency band between 1 and 20 Hz, accelerometers and velocity transducers of GEOS provide almost identical records after instrumental response correction, which we confirm using the records of a commonly observed M_W 3.3 earthquake. At the largest scale, we use theoretical Green's functions calculated by assuming two different 1D velocity structures, for northeast and southwest of San Andreas Fault [ Liu et al., 2006]. We invert the seismograms and obtain a successful multiscale source model of the 2004 Parkfield earthquake. At the largest scale, the rupture propagates mainly northwestward, as suggested by previous papers [ex. Liu et al., 2006]. In the first second of rupture, we find that slip is very slow (~ 0.2 m/s) but, after that, it rapidly accelerates to more than 3 m/s and propagates bilaterally. This is substantially different from the results of our previous study of the 2004 mid-Niigata prefecture, Japan, earthquake [ Uchide and Ide, 2007], which has the slip-rate faster than 1 m/s, even in the first 0.1 seconds. This difference might arise from different tectonic condition.
DE: 0520 Data analysis: algorithms and implementation
DE: 7209 Earthquake dynamics (1242)
DE: 7215 Earthquake source observations (1240)
SC: Seismology [S]
MN: 2007 Fall Meeting