HR: 0800h
AN: S41B-0985    [Abstracts]
TI: Crustal Heterogeneity in the Source Region of the 2004 Mid Niigata Prefecture Earthquake: Inversion Analysis of Coda Envelopes
AU: * Nishigami, K
EM: nishigam@eqh.dpri.kyoto-u.ac.jp
AF: DPRI, Kyoto University, Gokasho, Uji, Kyoto, 611-0011 Japan
AB: The 2004 Mid Niigata Prefecture earthquake (M 6.8) and its aftershock sequences generated complicated, i.e., several conjugate fault planes in their source region. In order to understand the generating process of these earthquakes, we estimated a 3-D distribution of relative scattering coefficients in the source region by inversion of coda envelopes of aftershocks. We analyzed 382 seismograms from 70 events which occurred on Nov. 1 to 7, recorded at 7 telemetry stations. The large slip area during the mainshock rupture seems to be a relatively homogeneous part on the fault, bounded by strong heterogeneous zones with larger scattering coefficients. Hypocenters of the mainshock and major large aftershocks with M 5-6 classes tend to be located close to stronger scattering areas. We found that one of these strong heterogeneities already existed before the occurrence of the M 5.9 aftershock on Nov. 8. We suppose that heterogeneous structures in the source region of this earthquake sequence affected the initiation and growth of ruptures of the mainshock and major large aftershocks. We will also discuss the temporal change and frequency dependency of scattering properties using a large data set of aftershocks.
DE: 7203 Body waves
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 7270 Tomography (6982, 8180)
DE: 8010 Fractures and faults
DE: 8015 Local crustal structure
SC: Seismology [S]
MN: Fall Meeting 2005