HR: 09:15h
AN: T11F-06    [Abstracts]
TI: A Time-Dependent Inversion Analysis for Short-Term Slow Slip Events in Southwest Japan Based on the NIED Hi-net Tiltmeter Data
AU: * Hirose, H
EM: hirose@bosai.go.jp
AF: National Research Institute for Earth Science and Disaster Prevention, 3-1 Tenno-dai, Tsukuba, 305-0006, Japan
AU: Sekine, S
EM: ssekine@bosai.go.jp
AF: National Research Institute for Earth Science and Disaster Prevention, 3-1 Tenno-dai, Tsukuba, 305-0006, Japan
AU: Obara, K
EM: obara@bosai.go.jp
AF: National Research Institute for Earth Science and Disaster Prevention, 3-1 Tenno-dai, Tsukuba, 305-0006, Japan
AB: In the deeper part of the southwest Japan subduction zone, a wide variety of "slow earthquakes," including low-frequency tremors (Obara, 2002), short-term slow slip events (SSE; Obara et al., 2004), and very low-frequency earthquakes (Ito et al., 2007), have occurred coincident with each other. Since SSEs have the maximum size (M_w~~ 6.0) and duration (several days) among them, the SSEs may control the overall characteristics of the coincident episodes, such as a recurrence rate, duration, and a migration velocity of the source region. In this context, it is important to know the source processes of the SSEs in order to understand not only the repeating nature of the coincident episodes, but also the generation cycles of megathrust earthquakes. We have applied a simple model that assumes a single rectangular fault to model tilt deformations due to the SSEs observed by the NIED Hi-net tiltmeter network (e.g., Hirose and Obara, 2005). This analysis is intended for estimating an approximate position and size of each event. The typical area of the estimated SSE faults has been 50~× 30~km². In practice, however, the observed tilt data show different time variations at different stations, or even for different directions at a particular station, during an episode. These facts indicate that the tilt records are capable of determining more detailed source processes for the SSEs. In this study, we developed a time-dependent inversion code that is applicable to the tiltmeter data, based on the Kalman filter approach (e.g., Segall and Matthews, 1997). We demonstrate that this method can resolve the slip histories for a number of SSEs in the western Shikoku region, southwest Japan. For the April 2006 western Shikoku episode, we assumed 5~× 3 subfaults with an area of 20~× 20~km² each, and the slip history was resolved as follows: the slip started in the base of the Sadamisaki Peninsula on April 16th, and the slip area extended to the east direction for the following four days. The temporal change in the estimated slip area corresponds roughly to the spatio-temporal distribution of the tremors in this episode. This result shows a closer spatial correspondence between the tremors and the SSE than ever indicated, suggesting that they have occurred at almost the same position.
DE: 1207 Transient deformation (6924, 7230, 7240)
DE: 1242 Seismic cycle related deformations (6924, 7209, 7223, 7230)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 7240 Subduction zones (1207, 1219, 1240)
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting