HR: 10:20h
AN: T32C-01 INVITED     [Abstracts]
TI: Crustal Deformation Around the Central-Northern Itoigawa-Shizuoka Tectonic Line Fault System, Central Japan, and its Tectonic Implications
AU: * Sagiya, T
EM: sagiya@seis.nagoya-u.ac.jp
AF: Nagoya University, Furo-cho, Chikusa-ku, Nagoya, 464-8602 Japan
AU: Nishimura, T
EM: t_nisimura@gsi.go.jp
AF: Geographical Survey Institute, Kitasato 1, Tsukuba, 305-0811 Japan
AU: Iio, Y
EM: iio@rcep.dpri.kyoto-u.ac.jp
AF: DPRI, Kyoto University, Gokasho, Uji, 611-0011 Japan
AB: The Itoigawa-Shizuoka Tectonic Line (ISTL) is a major geologic boundary dividing the Japanese mainland into the northeastern and the southwestern parts. Under the present compressive stress regime of the Japanese islands, active deformation is ongoing along ISTL. The ISTL fault system is considered to be one of the most active faults in the Japan Islands. In particular, the Gofukuji Fault has a slip rate of 8-9 mm/yr, which is the largest value for active faults in the Japanese inland. We investigated contemporary crustal deformation by deploying an array of permanent GPS (Global Positioning System) stations. The GPS observation demonstrates conspicuous shortening (about 0.3ppm/yr) around the East Matsumoto Basin Fault at Omachi city. This contraction is concentrated in a narrow zone of about 30km, indicating that a responsible deformation source is located at a shallow depth. On the other hand, the geodetic strain rate around the Gofukuji Fault is consistent with a geologically inferred left-lateral strike slip motion although the strain rate is much smaller (0.05 ppm/yr) compared with that around the East Matsumoto Basin Fault. The deformation is widely distributed around the Gofukuji Fault, and the relative displacement rate over 100km-long baseline across the fault is comparable to its geological slip rate. These observation data indicate that the strain accumulation is quite heterogeneous along ISTL. One explanation for this heterogeneity is a difference in the crustal structure. Seismological as well as electromagnetic structural exploration revealed a complicated upper crustal structure and a possible lower crustal heterogeneity beneath the East Matsumoto Basin fault. Such a heterogeneous structure reflects a geologic history of tectonic inversion in this area after the opening of the Japan Sea. Another factor to be considered is a transient deformation component in the interseismic period. There is no historical record of a large earthquake around the Gofukuji Fault, while the 1918 Omachi Earthquake (M6.5) occurred around Omachi city. Taking these factors into account, the present seismic potential is not proportional to the geodetic strain rate. Rather, the probability of earthquake occurrence is much larger at the Gofukuji Fault, as deduced from the geological exploration.
DE: 7223 Seismic hazard assessment and prediction
DE: 7230 Seismicity and seismotectonics
DE: 8123 Dynamics, seismotectonics
DE: 1208 Crustal movements--intraplate (8110)
DE: 1243 Space geodetic surveys
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting