HR: 0800h
AN: S31A-0213    [Abstracts]
TI: Crustal heterogeneity and its relation to seismic activity in the Kinki district, southwest Japan
AU: * Nishigami, K
EM: nishigam@eqh.dpri.kyoto-u.ac.jp
AF: Disaster Prevention Research Institute, Kyoto University, Gokasho, Uji, Kyoto, 611-0011, Japan
AB: It is essential to estimate detailed heterogeneous structures in and around the earthquake source region, in order to understand the generating process of earthquakes. Microseismicity is very high in the central to northern part of the Kinki district, southwest Japan. We will discuss the crustal heterogeneity in this region from a viewpoint of delineating its correlation with the earthquake occurrence in space and time. We estimated a 3-D distribution of relative scattering coefficients in the Kinki district by inversion of coda envelopes from local earthquakes. We analyzed 828 seismograms from 63 events which occurred in 2003, recorded at 50 stations of Kyoto Univ., Hi-net, and JMA. The result shows the existence of a remarkable scattering zone at a depth from 20 to 30 km, just below the high microseismicity area. The strong scattering zone is well correlated with the location of S-wave reflectors estimated by previous studies (Katao, 1993), and has revealed the heterogeneous structures in more detail. Deep low-frequency earthquakes occur at a depth of 30-40 km just below this strong scattering zone (Ohmi, 2002). From these, we consider that this scattering zone should have a strong influence on the active microearthquakes just above it, for example as supplying fluids to the seismogenic zone in the upper crust. We have a data base of earthquakes in recent 30 years in this region. We will also discuss the correlations between the temporal variation in microseismicity and that in scattering images, aiming at detecting some evidence of crustal fluids affecting the earthquake occurrence.
DE: 7203 Body waves
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 7270 Tomography (6982, 8180)
DE: 8015 Local crustal structure
SC: Seismology [S]
MN: 2007 Fall Meeting