HR: 0800h
AN: S41A-0969    [Abstracts]
TI: Spatial Relationship Between Crustal Structures and Seismic Activities
AU: * Hirose, I
EM: hirose@rcep.dpri.kyoto-u.ac.jp
AF: RCEP, DPRi, Kyoto University, Gokasho, Uji, Kyoto, 611-0011 Japan
AU: ITO, K
EM: ito@rcep.dpri.kyoto-u.ac.jp
AF: RCEP, DPRi, Kyoto University, Gokasho, Uji, Kyoto, 611-0011 Japan
AB: The purpose of this study is to investigate spatial relationship between crustal structures, seismic activities and active faults to reveal seismic process of the intraplate earthquakes. We analyze three seismic refraction and wide-angle reflection survey records conducted in the Kinki district, southwestern Japan. The survey lines are the Fujihashi-Kamigori profile line in 1989, the Keihoku-Seidan profile line in 1995 passing through the epicenter of the 1995 Kobe Earthquake (Mw6.8) and the Shingu-Maizuru profile line in 2004 carried out under the Special Project for Earthquake Disaster Mitigation in Urban Areas. Although the interval distances of the seismic stations of the Fujihashi-Kamigori and the Keihoku-Seidan profile lines are large (600m-1500m) since these records are the data for the refraction analysis, we attempt to analyze these data using by the typical seismic reflection analysis. The refraction analysis, as ray tracing method (Zelt and Smith, 1992), is also used to determine the velocity structures. As these three profile lines cross almost same area in the northern Kinki district, we can obtain the three dimensional crustal structure of a wide area. From the analyses of the reflections, we can obtain detailed reflection images from the surface down to the upper mantle. In particular, high-resolution images of the structure are obtained along the Shingu-Maizuru profile line, since high-density seismic stations and shot points are deployed. We find obvious horizontal reflectors at about 15km of depth, which is close to the lower cut off of the seismogenic layer in the crust. Recently, such reflectors have been reported in some areas in Japan (e.g. Matsumoto et al., 2000, Nishida et al., 2002). There seems to be any relationships between reflectors and intraplate earthquake; otherwise, are they seen at the brittle-plastic transition zone? Furthermore, we detect some north dipping reflectors under the large active faults, such as the Arima-Takatsuki Tectonic Line (ATL), the Median Tectonic Line (MTL), and the Yamasaki fault. Iio (1996) suggested that the slow slip on the reflector under the ATL detected by Katao (1994), possibly be a trigger of the 1995 Kobe Earthquake. The reflectors at the bottom of the active faults are thought to play an important role in the occurrence of the large earthquake and/or in the strain accumulation process.
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
SC: Seismology [S]
MN: Fall Meeting 2005