Features of initial rupture for the 2005 West Off Fukuoka Earthquake-Temporal evolution of the initial rupture
Abstract
It is a major question how the initial rupture process of a large earthquake differs from that of a smaller one. A P-phase with smaller amplitude (P1) that precedes a larger P-phase (P2) has often been observed for major seismic events (e.g., Umeda, 1990), which indicates that a small-scale rupture occurs at the initial phase before the rupture of asperity. Such two phases were observed for the 2005 West off Fukuoka Prefecture Earthquake that occurred on March 20, 2005 (MJMA = 7.0) . Kawakata et al. (2005) investigated the first small amplitude phase to know the initial rupture process. First, they checked whether these two phases were generated by different but adjacent ruptures along the fault, and relocated these hypocenters by means of the master event hypocenter relocation technique. They identified P1, P2, S1, and S2 (S-phases that correspond to P1 and P2) using AIC for AR model fitting. The distance and time interval between the two ruptures are consistent with spatio-temporal slip distribution estimated by Asano and Iwata (2006). The average rupture propagation speed of the initial rupture, defined from the distance and time interval of the two ruptures, was 1.02 km/s, which was significantly lower than the optimal first time window propagation speed of the whole main shock (2.1 km/s) reported by Asano and Iwata (2006). The moment magnitude of the initial rupture was estimated to be around 4.7. We estimated the source time functions for the initial rupture of the 2005 West off Fukuoka Prefecture Earthquake and aftershocks of similar size by means of the empirical Green's function method (e.g., Irikura, 1986). We used seismograms recorded by High Sensitivity Seismograph Network (Hi-net) deployed by NIED. It was found that the moment release of the initial rupture was emergent at the onset and had a long duration compared to typical aftershocks of the same size, indicating that the initial rupture process for the main shock differs from that of aftershocks.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2006
- Bibcode:
- 2006AGUFM.S31A0167Y
- Keywords:
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- 7200 SEISMOLOGY;
- 7209 Earthquake dynamics (1242);
- 7215 Earthquake source observations (1240)