HR: 0830h
AN: G21B-0265    [PDF]
TI: Reexamination of interplate coupling model in the Tokai region,based on the GPS data
AU: * Ohta, Y
EM: oota@eps.nagoya-u.ac.jp
AF: Graduate School of Environmental Studies, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, 464-8602 Japan
AU: Kimata, F
EM: kimata@seis.nagoya-u.ac.jp
AF: Graduate School of Environmental Studies, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, 464-8602 Japan
AU: Sagiya, T
EM: sagiya@seis.nagoya-u.ac.jp
AF: Graduate School of Environmental Studies, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, 464-8602 Japan
AB: The slow slip event is detected by continuous GPS measurements in the Tokai region, central Japan, where is the subduction zone of the Philippine Sea Plate (PHS), in 2001(Ozawa et al., 2002). Also a high-dense seismological network makes clear the plate boundary structure in this region with more detail. From such background, we reexamined about the interplate-coupling model based on the GPS measurements in the period of 1997 to 2000. Generally, as the PHS is subducting northwestward in the Suruga-Nankai Trough, southern central Japan, horizontal displacements with 1-2cm/year are detected by the national wide GPS network (GPS Earth Observation Network, GEONET) in the Tokai region (Sagiya et al., 2000). Vertical ground deformation observed by precise leveling, tide measurements and GPS measurements shows clearly a tilt toward trough. As a typical example, vertical movement shows a subsidence of 4-8mm/yr at Cape Omaezaki and an uplift of 3-4mm/yr at Nagoya in western Tokai region. Great thrust earthquakes of magnitude 8 have occurred repeatedly in the period of 100-150 years. Interplate coupling in the Tokai region are discussed from the seismic data by Matsumura [1997], and from the GPS data by Sagiya[1999]. Aoki et al (2003) also estimate the interplate coupling using the vertical deformation detected by GPS measurements, but they discuses the coupling only along the one direction toward northwest. However these back-slip distribution are disaccord each models. We applied the inversion method of Yabuki and Matsu'ura(1992) and estimated distribution of back-slip on the plate boundary. The back-slip model is a way of interpreting interseismic deformation in terms of virtual fault slip on the plate boundary [Savege, 1983]. Geometry of the plate boundary is determined from hypocenter data by Japan Meteorological Agency (JMA). For the inversion analysis, we extracted 70 GPS stations of GEONET in the Tokai region in the period from April 1997 to May 2000,and we process the GPS data at each site using PPP method of GIPSY/OASIS II. Back-slip distributes within 20-25mm/year at the 15-20km depth of the plate boundary, which show the agreement with the convergent rate of PHS plate along the Suruga trough (Miyazaki and Heki, 2001). Maximum back-slip rate is detected in the area between Atsumi Peninsula and Hamana Lake, which is the eastern adjacent area of the 1944 Tonakai earthquake fault (Yamanaka et al., 2003). A back-slip rate is smaller along the Suruga trough than that along the Nankai trough. A subsidence observed at Omaezaki is calculated with more detailed from the back-slip model. However, an uplift detected around western Tokai region is not synthesized completely from our back-slip model. It suggests Niigata-Kobe Tectonic Zone is related to the uplift.
DE: 1206 Crustal movements--interplate (8155)
SC: Geodesy [G]
MN: 2003 Fall Meeting