Estimation of Source Spectrum of the 2005 Miyagi-oki Earthquake and Attenuation and Site Amplification Factors around Miyagi Prefecture, Japan
Abstract
We estimated a source spectrum of the 2005 Miyagi-oki earthquake (MJMA7.2) and 11 events (4.0JMA<5.0) consisting of inter-plate and inland earthquakes occurred around Miyagi region applying the spectral inversion method to seismic records observed at KiK-net stations in Miyagi prefecture. Attenuation and site amplification factors were also estimated. Before applying the method, geometrical spreading factor was estimated as a function of frequency using the twofold spectral ratios. It was successfully estimated at frequency ranges from 3 to 20 Hz. The average is represented as 1.12±0.27. Applying the value to the geometrical spreading factors for all frequency ranges (0.3 Hz to 20 Hz), we performed the spectral inversion method for the data recorded at 12 KiK-net stations in Miyagi prefecture. As a result the attenuation factor (1/Qs) of shear waves was successfully estimated at frequency ranges above 3 Hz. The frequency dependent 1/Qs can be approximated by Qs(f)-1=(5.0 × 10-3) f^{-0.8} at frequency range 3 to 12 Hz. We found that total attenuation effect including geometrical spreading and attenuation effects does not so contribute to the observed strong acceleration at short period range. Short-period spectral level of mainshock on the 2005 Miyagi-oki earthquake estimated from the source spectrum is roughly two times as large as those expected from the empirical rule for the event with same seismic moment. These results indicate that high level of short-period source spectrum of mainshock contributed to the observed strong acceleration at short period range in Miyagi region.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2006
- Bibcode:
- 2006AGUFM.S13C0250M
- Keywords:
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- 7200 SEISMOLOGY;
- 7212 Earthquake ground motions and engineering seismology;
- 9320 Asia