| Project/Area Number |
04640394
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
固体地球物理学
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| Research Institution | TOHOKU UNIVERSITY |
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Principal Investigator |
OHTAKE Masakazu Tohoku Univ. Geophysical Institute, Professor, 理学部, 教授 (60203816)
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| Co-Investigator(Kenkyū-buntansha) |
SATO Haruo Tohoku Univ. Geophysical Institute, Associate Prof., 理学部, 助教授 (80225987)
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| Project Period (FY) |
1992 – 1993
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| Project Status |
Completed (Fiscal Year 1993)
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| Budget Amount *help |
¥1,700,000 (Direct Cost: ¥1,700,000)
Fiscal Year 1993: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 1992: ¥1,200,000 (Direct Cost: ¥1,200,000)
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| Keywords | seismic wave / source spectrum / stress drop / attenuation / scattering / site effect / 火山フロント / 地盤の増巾特性 / スペクトル |
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| Research Abstract |
For assessing the regionality of earthquake source spectra, we analized waveforms of micro- to small-sized earthquakes ocurring in different regions in Japan. One of the most important results is the finding of systematic difference in stress drop for shallow earthquakes occurring in the aftershock region of the 1984 Naganoken-Seibu earthquake (M=6.8) and in the Asio region where stationary seismic activity is observed. Detailed analysis of waveforms revealed that the ratio of P to S wave attenuation is higher than unity in contrast to past studies. We also revealed that site amplification effect is not negligible even at hard-rock observatiion sites for high-frequency seismic waves. We further attempted to separate the effects of seismic wave dissipation due to intrinsic attenuation and scattering, based on the theoretical formulation of scattering behavior that was done in this study. The theoretical work includes formulation of analitic solutions of the two-dimensional multiple isotropic scattering, and seismogram envelope synthetics including P-S conversions.
The broad-band seismometer that was newly installed by this study is in full operation, and the observation is to be continued. The high quality date from this observation will largely contribute to extend our study to larger earthquakes.
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