Source and Path Modeling of the 2001 Geiyo Earthquake and the Strong Ground Motions
Abstract
Intraplate earthquakes occurring within subducting slabs (slab earthquakes) can give large damage to the cities located above. In this study, detailed source process of the 2001 Geiyo earthquake (Mw = 6.8), which is a normal fault event occurring in the subducting Philippine Sea plate beneath southwest Japan, is investigated from the inversion of high-density strong ground motion waveforms. For the inversion, the S-wave part velocity waveforms (0.1 - 0.5 Hz) at the NIED K-NET and KiK-net stations are used. Analysis of the waveforms at the 13 stations surrounding the source area indicates a bending fault model, which is roughly composed of the two segments with different strike and dip angles, respectively. The slip distribution on the fault plane obtained from the waveform inversion is rather heterogeneous. The Philippine Sea slab in this area is composed of the high-velocity slab mantle and the overlying low-velocity slab (oceanic) crust with thickness of 6 km. The rupture, which started within the slab mantle, not only spread in the high-velocity slab mantle but also invaded into the low-velocity slab crust. Large slip is seen both in the slab mantle and in the slab crust. The rupture propagated almost unilaterally from the north to the south. Comparison of the observed waveforms at the northern (backward-directivity side) and the southern (forward-directivity side) clearly shows the directivity effect on the strong ground motion waveforms. The detailed irregularities of the complex rupture process appear more clearly on the backward-side waveforms. The Green's functions are calculated using flat-layered underground structure models. An aftershock with Mw 5.2 is used as a path-calibration event, and the station-specific shallow sediment layer models are constructed by trial and errors by comparing the observed and synthetic waveforms of this event. The total seismic moment of the 2001 Geiyo earthquake is 2.3 x 10E+19 N*m. The previously estimated seismic moment based on the underground structure model without the shallow sediment layers was 3.1 x 10E+19 N*m. This shows that source inversion without considering shallow sediment layers can inappropriately attribute the amplification effect by soft layers to the source and overestimate the source factor.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2003
- Bibcode:
- 2003AGUFM.S52A0113K
- Keywords:
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- 7209 Earthquake dynamics and mechanics;
- 7212 Earthquake ground motions and engineering;
- 7215 Earthquake parameters;
- 7223 Seismic hazard assessment and prediction