HR: 0800h
AN: G51B-0817    [Abstracts]
TI: Change of Strain Rate in the Kinki and Tokai Districts, Japan, Induced by the Tokai Slow Slip Event
AU: * Kobayashi, T
EM: tkoba@rcep.dpri.kyoto-u.ac.jp
AF: DPRI, Kyoto Univ., Gokasho, Uji, 611-0011 Japan
AU: Hashimoto, M
EM: hasimoto@rcep.dpri.kyoto-u.ac.jp
AF: DPRI, Kyoto Univ., Gokasho, Uji, 611-0011 Japan
AB: We evaluated the temporal variation of the strain rate in around Kinki and Tokai region, Japan, by using continuous GPS data (GEONET data) from 1996 to 2004. It was found from the result that the strain rates remarkably decreased in the east of Lake Biwa including the Yoro and Neodani faults from the latter half of 2000. Our inversion results showed the change of strain rates can be well explained by the non-steady slow slip event (SSE) beneath the Tokai area. Furthermore, we found that the seismicity decreased as well as strain rates in this area. In order to estimate the strain rates, we applied a method by Shen et al. (1996). In this method, we solve an observation equation that an observed velocity is related to horizontal velocity, strain rates, and a rotation rate at an arbitrary point on the two-dimensional plane, with a weight of Gaussian type depending on the distance between a station and a calculation point. We used F2 solutions of GEONET data, and estimated a velocity by using the time series data composed of daily positions. As a result, we found that the contraction remarkably decreased in the east of Lake Biwa from the latter half of 2000. This decrease reached as much as 0.1 ppm at some points. Furthermore, it is remarkable that the principal axes of contraction changed its direction from northwest-southeast to east-west, and then an extensional component became dominant simultaneously. The start of the change almost corresponds to that of the Tokai SSE. Next, we estimated the slip distribution of the Tokai SSE. We here set point sources on the plate boundary between the Eurasia and Philippine Sea plates beneath Tokai region. The slips were estimated from the non-steady displacements on the ground surface by a least square method. To stabilize the solution, we here impose a smoothness constraint on the slip distribution. The predicted strain rates deduced from the estimated Tokai SSE can reconstruct well the above features of the strain rate change in the east of Lake Biwa. It suggests that the Tokai SSE affected the strain rate in the region where the slow slip area is away from more than 100 km. Moreover, we investigated the seismicity in the east of Lake Biwa, using a declustering procedure by Reasenberg (1985), and found that the occurrence rate also decreased from the latter half of 2000 as well as the strain rates.
DE: 1207 Transient deformation (6924, 7230, 7240)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
SC: Geodesy [G]
MN: Fall Meeting 2005