1991 Fiscal Year Final Research Report Summary
High frequency seismic observation at the borehole which reaches an earthquake fault
| Project/Area Number |
02452054
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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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 | Kyoto University |
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Principal Investigator |
IIO Yoshihisa Kyoto Univ., D. P. R. I., Research associate, 防災研究所, 助手 (50159547)
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| Co-Investigator(Kenkyū-buntansha) |
ANDO Masataka Kyoto Univ., D. P. R. I, Professor, 防災研究所, 教授 (80027292)
SATO Haruo Tohoku Univ., F. of Science, Assistant prof., 理学部, 助教授 (80225987)
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| Project Period (FY) |
1990 – 1991
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| Keywords | borehole / seismic source spectrum / high frequency / earthquake fault / ultra-microearthquake / initial phase |
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| Research Abstract |
Three components of selsmometers were installed at the borehole which reached the earthquake fault of the 1984 Western Nagano Prefecture, Japan Eartqhauke. A lot of seismograms from microearthqaukes were recorded the observation system which had a frequency response up to 1 kHz and a wide dynamic range of 96 dB.
It is found that the onset of P-waves from microeartqhaukes arrives much earlier than that detected with a usual seismic station and observation system.
It is made clear that the initial rise of P-waves of microearthquakes is fairly smooth and that it does not act as a ramp in time. This fact is different from that predicted by a lot of theories which had been previously published.
It is deduced that the source process of microeathquakes is fairly slow at the beginning of rupture growth. It is possible that this slow process includes the key for the rupture growth.
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