HR: 1340h
AN: S13D-1094    [Abstracts]
TI: Numerical Investigation of the Effects of Anisotropy in a Fault Zone on Seismic Wavefield
AU: * Nakamura, T
EM: nakamura@geo.kyushu-u.ac.jp
AF: Department of Earth and Planetary Sciences, Kyushu University, Hakozaki 6-10-1, Fukuoka, 812-8581 Japan
AU: Takenaka, H
EM: takenaka@geo.kyushu-u.ac.jp
AF: Department of Earth and Planetary Sciences, Kyushu University, Hakozaki 6-10-1, Fukuoka, 812-8581 Japan
AB: The physical properties in and around the fault zone has came under intense study and observational data using dense seismic array network near the fault zone enables us to obtain the general view of spatial distribution of anisotropy associated with the fault zone such as fractures or cracks. Based on these anisotropic distributions, in this study we make and analyze the synthetic seismogram in order to estimate the influence of anisotropy in the fault zone on seismic wavefield. The propagator matrix method is used to calculate synthetic seismograms for a vertically layered medium. In the synthetic seismograms a later phase can be seen just after the main S-wave, and the separation between them are proportional to the propagation distance in the anisotropic fault zone and the degree of anisotropy. We suggest that observing and analyzing the later phase could be a clue to detect the fault zone. We also find that in the strike slip source with the strike parallel to the fault zone the synthetic seismograms are more affected by the velocity structure than the anisotropy. This means that it is difficult to estimate the shear wave splitting parameters describing the degree of anisotropy and the direction of symmetry axis from the waveform records for such source mechanism. However, the shear wave splitting parameters are available in the case of the normal-fault or reverse-fault source, and also in the case of the strike slip, normal fault and reverse fault striking 45 degrees against the strike of the fault zone. We suggest that the mechanism solution is needed for estimating the anisotropy in the fault zone.
DE: 7200 SEISMOLOGY
DE: 7203 Body wave propagation
DE: 7205 Continental crust (1242)
SC: Seismology [S]
MN: 2004 AGU Fall Meeting