HR: 1340h
AN: S23B-0327    [Abstracts]
TI: Crustal heterogeneity in active fault regions estimated by inversion of coda envelopes
AU: * Nishigami, K
EM: nishigam@rcep.dpri.kyoto-u.ac.jp
AF: Disaster Prevention Research Institute, Kyoto University, Gokasho, Uji, Kyoto, 611-0011 Japan
AU: Jin, A
AF: ADEP/NIED, 3-1 Tennodai, Tsukuba, Ibaraki, 305-0006 Japan
AB: Coda envelopes from local earthquakes can be inverted to estimate a 3D heterogeneous structure in the crust (Nishigami, 1991, 2000; Asano and Hasegawa, 2004). These studies suggest that the data of dense seismographic networks is effective to image crustal heterogeneities and also it is possible to estimate deep structure of active faults such as downward extension in the crust, segmentation along the fault, and relatively weaker scattering (i.e., more homogeneous or locked) areas which will be ruptured by M 6-7 earthquakes. Recently High Sensitivity Seismograph Network (Hi-net) has been constructed by NIED covering all over Japan. We are aiming at estimating systematic variation in the crustal heterogeneity in Japan and trying to detect a possible structure related to the earthquake generation, using the Hi-net, and University and JMA network data. We analyzed two active fault regions, the Yamasaki fault system in southwest Japan and the Atotsugawa fault system in central Japan. The deviation of coda envelopes from average decay curves was measured as the observational data assuming a single isotropic scattering model. The analysis area, $\sim$200 km in horizontal and $\sim$60 km in depth, was divided into small blocks, and 3D distribution of relative scattering coefficient was obtained by solving the observational equation using a recursive stochastic inversion. The result shows strong scattering along the entire Yamasaki fault system at the seismogenic depth of 10-15 km. For the Atotsugawa fault system, we can find weaker scattering along the Ushikubi fault, which is one branch of the fault system and shows low microseismicity. The resolution will be improved by adding more data including the University and JMA stations, and the deep heterogeneous structure of these active faults will be discussed.
DE: 8180 Tomography
DE: 7230 Seismicity and seismotectonics
DE: 8015 Local crustal structure
SC: Seismology [S]
MN: 2004 AGU Fall Meeting