HR: 0800h
AN: G11A-0770    [Abstracts]
TI: Recent Crustal Deformations In Kii Peninsula, Southwest Japan Derived From Dense GPS Observations: Interplate Coupling And 2004 Earthquake Sequence SE Off Kii Peninsula
AU: * Hashimoto, M
EM: hasimoto@rcep.dpri.kyoto-u.ac.jp
AF: DPRI, Kyoto Univ., Gokasho, Uji, Kyoto, 611-0011 Japan
AU: Onoue, K
EM: onoue@rcep.dpri.kyoto-u.ac.jp
AF: DPRI, Kyoto Univ., Gokasho, Uji, Kyoto, 611-0011 Japan
AU: Ohya, F
EM: ohya@rcep.dpri.kyoto-u.ac.jp
AF: DPRI, Kyoto Univ., Gokasho, Uji, Kyoto, 611-0011 Japan
AU: Hoso, Y
EM: hoso@rcep.dpri.kyoto-u.ac.jp
AF: DPRI, Kyoto Univ., Gokasho, Uji, Kyoto, 611-0011 Japan
AU: Sato, K
EM: sugar@rcep.dpri.kyoto-u.ac.jp
AF: DPRI, Kyoto Univ., Gokasho, Uji, Kyoto, 611-0011 Japan
AU: Segawa, K
EM: segawa@rcep.dpri.kyoto-u.ac.jp
AF: DPRI, Kyoto Univ., Gokasho, Uji, Kyoto, 611-0011 Japan
AU: Fujita, Y
EM: fujita@rcep.dpri.kyoto-u.ac.jp
AF: DPRI, Kyoto Univ., Gokasho, Uji, Kyoto, 611-0011 Japan
AB: Kii peninsula, southwest Japan is located close to the Nankai trough and suffers from the subduction of the Philippine Sea plate. Deeper part of the source region of interplate earthquakes, such as 1946 Nankai is beneath this peninsula. Therefore it is important to reveal detailed crustal deformations in this area for the purpose of understanding of generation process of interplate earthquakes and long-term forecast of their occurrence. We established 10 GPS observation sites filling the gaps of the GEONET operated by GSI along two lines nearly parallel to the relative motion between the Philippine Sea and Amurian plates. Resultant average spacing is 5~10km. We have repeated the campaign survey of this traverse using dual-frequency receivers since March 2001. So far, we have collected data from 4 campaigns done every March and can discuss displacement/velocity field during the recent 3 years. We calculate coordinates of our campaign sites with GSI_fs permanent sites in ITRF2000. We use the GIPSY/OASIS II software with JPL precise ephemeredes in the analysis. Velocity of each site is calculated referring to the first campaign and converted to the relative velocity to the Amurian plate using the Euler vector by Heki et al. (1999). Velocities derived from 2001 and 2002 campaigns are about 20mm/yr in the middle part of Kii peninsula and 35mm/yr at its southern tip, respectively, relative to the Amurian plate. Their directions are WNW. The gradient is almost linear up to 33.8N and there is no significant change in gradient in northern part. Velocities along the eastern line are a little smaller than those on the western line. We apply a model with multiple fault segments to this velocity field and estimate their slip deficit rates. We adopt the 9 segments around Kii peninsula from the fault model of Sagiya and Thatcher (1999). Estimated slip deficit rates are as large as 70 mm/yr that is slightly larger than the relative plate motion. If we add deeper extension to the modeled fault, slip deficit rates of about ~60 mm/yr are obtained. If we subtract a 10mm/yr nearly westward block motion, which proposed by several researchers, from the observed velocities, slip deficit rates are significantly reduced. However we obtain slip deficit rate larger than 40mm/yr in the transition zone estimated by Hyndman et al.(1995). These results imply that significant strains are being accumulated in the transition zone as well as the main locked zone. Two earthquakes of Mjma larger than 7 occurred southeast off Kii Peninsula on September 5, 2004. GEONET of GSI revealed southward motion up to 5cm in the eastern part of Kii peninsula. We have started reoccupation of our sites and will hopefully observe co- and postseismic deformations due to this activity.
DE: 7230 Seismicity and seismotectonics
DE: 8123 Dynamics, seismotectonics
DE: 1206 Crustal movements--interplate (8155)
DE: 1242 Seismic deformations (7205)
DE: 1243 Space geodetic surveys
SC: Geodesy [G]
MN: 2004 AGU Fall Meeting