HR: 1330h
AN: S42A-0139    [PDF]
TI: Spatial and Temporal Correlation Between Nonvolcanic Low-frequency Tremors and Slow Slip Events Detected in the Southwest Japan Subduction Zone
AU: * Obara, K
EM: obara@bosai.go.jp
AF: NIED(National Research Institute for Earth Science and Disaster Prevention), 3-1, Tennodai, Tsukuba, 305-0006 Japan
AU: Hirose, H
EM: hirose@bosai.go.jp
AF: NIED(National Research Institute for Earth Science and Disaster Prevention), 3-1, Tennodai, Tsukuba, 305-0006 Japan
AB: Megathrust earthquakes of magnitude greater than 8 have repeatedly occurred in southwest Japan due to the subduction of the Philippine Sea plate. Recently, non-volcanic seismic tremors have been discovered in the fore-arc side of the subducting plate (Obara, 2002) by analyzing the continuous records of the high-density high-sensitivity seismograph network, NIED Hi-net. The tremors are not distributed homogeneously in the narrow belt along the strike of the slab but spatially clustered. The major activity of the tremor is also clustered periodically, with a period of 2 or 3 months in the east and middle part of Shikoku area, and about 6 months in the west of Shikoku. Every Hi-net observatory is equipped with a high-sensitivity accelerometer, which has wide range in frequency response. Output from horizontal components of the accelerometer can be analyzed as tilt movement. In the west of Shikoku, we found that step-like tilt changes occurred four times in two years of 2001 and 2002 associated with periodic major tremor activities. Each tilt change continues for a few days at the stations near the source area of the tremor. The duration of the tilt change is simultaneously associated with the major activity of the tremor. The tilt step is about 0.1 micro radian in maximum. Based on the observed tilt step the slow slip event is estimated to occur on a reverse fault at around the interface of the subducting Philippine Sea plate. The simultaneous activity of the tremors and the slow slip events is very similar to ETS (Episodic tremor and slip) detected in Cascadia subduction zone (Rogers and Dragert, 2003). Both observations in young subduction zones might be important for understanding the condition of the transition zone on the plate boundary and monitoring the stress accumulation at the locked section of the slab.
DE: 1206 Crustal movements--interplate (8155)
DE: 1236 Rheology of the lithosphere and mantle (8160)
DE: 7230 Seismicity and seismotectonics
DE: 8045 Role of fluids
DE: 8150 Plate boundary--general (3040)
SC: Seismology [S]
MN: 2003 Fall Meeting