HR: 11:35h
AN: G22A-06    [Abstracts]
TI: Groundwater-Level Anomalies Associated with a Hypothetical Preslip Prior to the Anticipated Tokai Earthquake: Evaluation of Detectability Using the Groundwater Observation Network of AIST
AU: * Matsumoto, N
EM: n.matsumoto@aist.go.jp
AF: Geological Survey of Japan, AIST, AIST Central 7, 1-1-1 Higashi, Tsukuba, 305-8567, Japan
AU: Kitagawa, Y
EM: y-kitagawa@aist.go.jp
AF: Geological Survey of Japan, AIST, AIST Central 7, 1-1-1 Higashi, Tsukuba, 305-8567, Japan
AU: Koizumi, N
EM: koizumi-n@aist.go.jp
AF: Geological Survey of Japan, AIST, AIST Central 7, 1-1-1 Higashi, Tsukuba, 305-8567, Japan
AB: A large earthquake of M 8 has been anticipated along the Suruga trough, offshore from central Japan. This anticipated earthquake is referred to as the Tokai earthquake, and the Japanese Government has maintained an earthquake prediction program for this earthquake since 1978. The National Institute of Advanced Industrial Science and Technology (AIST) has been monitoring groundwater levels in the Tokai region since 1978. As of 2007, AIST continuously monitors 15 wells at nine observation sites in the Tokai region. We infer the groundwater-level anomalies associated with a hypothetical preslip prior to the anticipated M8 Tokai earthquake, and evaluate the detectability of the anomalies using data from seven groundwater wells. We evaluate the detectability of the anomalies under the following assumptions: (1) an Mw 5.5 - 6.5 aseismic preslip event occurs at the plate boundary in and around the hypothetical focal zone of the Tokai earthquake; (2) the total amount of the strain step at each observation associated with the preslip can be calculated by tensile and shear faulting based on the dislocation model; (3) a normalized strain history associated with the preslip is defined from the results of numerical simulations based on rate- and state-dependent friction laws; and (4) the groundwater-level anomaly prior to the earthquake is proportional to the estimated history of the strain change associated with the preslip. We investigate the detection time of the anomaly at seven wells given an Mw 5.5, 6.0, or 6.5 aseismic preslip at one of the 272 grid points in and around the area of the hypothetical focal zone of the Tokai earthquake. As a result, over the time interval between 1 and 48 hours prior to the hypothetical Tokai earthquake, we are able to detect at each of the seven wells a hypothetical Mw 6.5 preslip at 10-86 of the 272 grid points, an Mw 6 preslip at 0-19 grid points, and an Mw 5.5 preslip at 0-5 grid points.
DE: 1209 Tectonic deformation (6924)
DE: 7223 Earthquake interaction, forecasting, and prediction (1217, 1242)
DE: 9320 Asia
SC: Geodesy [G]
MN: 2007 Fall Meeting