HR: 0800h
AN: G11A-0765    [Abstracts]
TI: Slow slip events estimated from ground deformation and seismic wave velocity structure estimated from seismic wave tomography in the Tokai region, Japan
AU: * KIMATA, F
EM: kimata@seis.nagoya-u.ac.jp
AF: Nagoya University, Furo-machi, Nagoya, 4648602 Japan
AU: OHOTA, Y
AF: Nagoya University, Furo-machi, Nagoya, 4648602 Japan
AU: NEGISHI, H
AF: National Research Institute or Earth Science and Disaster Prevention, Tenno-dai, Tsukuba, 3050006 Japan
AU: MATSUBARA, M
AF: National Research Institute or Earth Science and Disaster Prevention, Tenno-dai, Tsukuba, 3050006 Japan
AB: Ohota et al. (2004) estimated the fault model of the 2001 Tokai slow slip event based on the re-processing GPS data comparing the ground deformation in 1997-2000. From their discussion, in the period of slow slip event, interplate coupling is tightly remained in the depth of 10-25 km in the plate boundary in the Tokai region. Forward slip consisting of slow slip event is ongoing with a rate of 3 cm/yr at the depth of 25-40 km in the plate boundary. The slow slip event fault locates outside of the 1944 Tonankai earthquake fault model by Tanioka and Satake (2002). It suggests that slow slip event is occurred outside of asperity area of historical large earthquakes along the Nankai Trough. Recently dense seismological network is constructed and seismic wave velocity structure are discussed with detail from the seismic wave tomography method (Matsubara et al.,2004; Kamiya and Kobayashi, 2004). According to their resolution, the low Vp and Vs layer is estimated in the 25-40 km depth of the plate boundary between the Philippine Sea plate and Eurasian plate in the Tokai region. Precisely we discus the location of low Vp and Vs layers, it is located upper part pf the plate boundary with width of 10km, which is corresponded to the lower continental crust..It is located just under northern area of Lake Hamana and Mikawa Bay. Kodaira et al.(2004), they conclude that high Vp/Vs ration distributed in subducting upper ocean crust around 30 km depth of the plate boundary is a occurrence mechanism of the 2001 Tokai slow slip event. From our research, the rate of Vp/Vs in upper part of the subducting oceanic crust is changing with the depth of the plate boundary. Until 25 km depth, velocities of P-wave and S-wave are not low, and the rate Vp/Vs is normal. At depth of 25 - 40 km, velocities of P-wave and S-wave are decreasing, and the rate Vp/Vs is increasing. The depth of high rate is correspond the slow slip fault estimated by Ohota et al.(2004) and hypocenters of unvolcanic low frequency tremore observed by Obara et al.(2002). If high Vp/Vs rate is depend on the dehydration of the subducting oceanic crust, it is suggested that around Lake Hamana, an upper part of subducting crust is dehydrating at the 25 km depth of plate boundary, and dehydrating is triggered the slow slip events and tremors.
UR: http://members8.tsukaeru.net/kimata/presen_at%20_meeting.html
DE: 8180 Tomography
DE: 8105 Continental margins and sedimentary basins
DE: 8150 Plate boundary--general (3040)
SC: Geodesy [G]
MN: 2004 AGU Fall Meeting