HR: 17:15h
AN: S54A-06    [Abstracts]
TI: 3-D Velocity Structure Modeling and Source Process Inversion: The 2003 Miyagi-ken Hokubu, Japan, Earthquake Sequence
AU: Hikima, K
EM: hikima@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: * Koketsu, K
EM: koketsu@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-0032 Japan
AB: At 7:13 a.m. on July 26, 2003 (JST), an M6.4 earthquake occurred in the northern part of the Miyagi prefecture, northeastern Japan. This mainshock was associated with a distinct foreshock (M5.6) and vital aftershock activities (M5.5 for the largest). They form the earthquake sequence called `the 2003 Miyagi-ken Hokubu earthquake sequence.' The results of seismic tomography and reflection surveys carried out after the sequence suggest a complex crustal structure in and around the source region of the earthquakes (Okada et al., 2004; Kato et al., 2004). This implies that the modeling of a 3-D velocity structure is crucial for waveform analyses such as a source process inversion and they should be greatly influenced by the choice of Green's functions. We first compiled the results of various explorations and constructed the initial model of the crustal velocity structure. 1-D and 2-D inversions of aftershock seismograms were performed for the velocity structure using this initial model and a similar method to that in Ichinose et al. (2003). We then combined the results into the final 3-D velocity model. The Green's functions for the source process inversion were calculated by finite difference codes with the reciprocity theorem and the 3-D model discretized at intervals of 200m. Since the detailed distribution of aftershocks indicates a curved fault plane (Okada et al., 2003), we modeled it with flexible triangular subfaults. The source process inversion of KiK-net and K-NET seismograms with the 3-D Green's functions indicates the primary asperity to be located in the middle of the northern half of the fault plane, though the inversion with Green's functions for 1-D velocity models recovered it in a shallow part above the center of the fault plane (Hikima and Koketsu, 2004). The agreement between the observed and simulated seismograms has significantly been improved in the 3-D result, which is consistent with the result of an inversion of geodetic data (Miura et al., 2004).
DE: 7203 Body wave propagation
DE: 7209 Earthquake dynamics and mechanics
DE: 7212 Earthquake ground motions and engineering
SC: Seismology [S]
MN: 2004 AGU Fall Meeting