HR: 1330h
AN: S52B-0136    [PDF]
TI: Correlating Seismicity and Subsidence in the Tokai Region, Central Japan
AU: Wiemer, S
EM: stefan@seismo.ifg.ethz.ch
AF: Swiss Seismological Service, ETH Zurich, Hoenggerberg, HPP, Zurich, 8093 Switzerland
AU: * Woessner, J
EM: woessner@seismo.ifg.ethz.ch
AF: Swiss Seismological Service, ETH Zurich, Hoenggerberg, HPP, Zurich, 8093 Switzerland
AU: Yoshida, A
EM: ayoshida@met.kishou.go.jp
AF: Kakioka Magnetic Observatory, Japan Meteorological Agency, Kakioka, 315-0116 Japan
AU: Hosono, K
EM: hosono@eqvol.kishou.go.jp
AF: Seismological and Volcanological Department, Japan Meteorological Agency, Tokyo, 163 Japan
AU: Noguchi, S
EM: shin@bosai.go.jp
AF: National Research Institute for Earth Science and Disaster Prevention, 3-1,Tennodai, Tsukuba, 305
AU: Takayama, H
EM: hirtakay@mri-jma.go.jp.
AF: Meteorological Research Institute, Japan Japan Meteorological Agency, Tsukuba, 305 Japan
AB: We investigate the correlation between seismicity rate changes as well as changes in the earthquake size distribution (b-value) of earthquakes and transients in geodetic data in the Tokai area of Central Japan. As a first target, we analyze the period of accelerated subsidence in the period 1988 - 1990. Three largely independent seismic catalogs cover this region: NIED, JMA and JUNEC, offering a unique opportunity to verify seismicity anomalies based on independent sources. We spatially and temporally map out seismicity rates, finding that a significant decrease in the earthquake rate of M $>$ 2.0 events coincides with the accelerated subsidence period; however, this anomaly disappears when including smaller magnitudes in the analysis. This relative quiescence of larger events can readily be explained when interpreting the transient in seismicity in the framework of a change in the earthquake size distribution, or b-value. The background b-value of about 0.8 increased in the period 1987.5 to 1989.5 to a value of b=1.2 and is confirmed in all three data sets. This b-value transient occurred in the immediate vicinity of a patch of low b-value in the centre of Suruga Bay (b=0.5) that could be interpreted as a major locked patch or asperity. We also analyze stress tensor inversions of NIED focal mechanism data, finding an increase in thrusting type earthquakes for the anomalous period show. While a unique interpretation of the relationship between subsidence, b-value and stress tensor inversion results is not possible, we propose that an increase in the locking strength, a slow stick event, is consistent with all observations. We are now investigating the seismicity transients accompanying the recent slow slip event that started in the year 2000. Our ultimate goal is to construct a quantitative model that relates micro-seismicity and deformation data in the Tokai region.
DE: 7223 Seismic hazard assessment and prediction
DE: 7230 Seismicity and seismotectonics
SC: Seismology [S]
MN: 2003 Fall Meeting