2001 Fiscal Year Final Research Report Summary
Study on detailed rupture processes and generation mechanism of strong ground motions by dense array observations in an earthquake swarm area
| Project/Area Number |
10490010
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
広領域
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| Research Institution | The University of Tokyo |
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Principal Investigator |
KOKETSU Kazuki Earthquake Research Institute, The University of Tokyo, Associate Professor, 地震研究所, 助教授 (90134634)
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| Co-Investigator(Kenkyū-buntansha) |
YAMANAKA Yoshiko Earthquake Research Institute, The University of Tokyo, Research Associate, 地震研究所, 助手 (30262083)
FURUMURA Takeshi Earthquake Research Institute, The University of Tokyo, Associate Professor, 地震研究所, 助教授 (80241404)
KIKUCHI Masayuki Earthquake Research Institute, The University of Tokyo, Professor, 地震研究所, 教授 (20046147)
TAKEO Minoru Earthquake Research Institute, The University of Tokyo, Professor, 地震研究所, 助教授 (00197279)
IDE Satoshi Earthquake Research Institute, The University of Tokyo, Research Associate, 地震研究所, 助手 (90292713)
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| Project Period (FY) |
1998 – 2001
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| Keywords | earthquake swarm / strong motion observation / earthquake rupture process / underground structure / 強振動 |
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| Research Abstract |
For investigating detailed rupture processes and generation mechanism of strong ground motions, we deployed a dense strong-motion observation array in the off-Ito area of the Izu peninsula region, where earthquake swarm activities were repeated and another one can be expected during the term of this project. However, any activity has not yer occurred in these four years after the previous swarm from March to June 1998, and so we also carried out mobile observations in the northern Izu islands region, where the eruption of Miyakejima induced a swarm of earthquakes in 2000. They brought us a huge dataset of strong motion records for many middle-size earthquakes including thirty-one M5 events and five M6 events.
For the off-Ito area of the Izu peninsula region, we analyze the strong motion records observed at 384 stations in the Kanto basin for the 1998 Izu Toho Oki earthquake (M5.7) immediately before the project term. Such a strike-slip event in Izu or the Sagami bay as this earthquake often generates dominant surface waves called Love waves for rather long-period strong motions in the Kanto basion, and their generation and propagation are controlled by the three-dimensional structure of the basin. We then carry out moment tensor inversions and tomographic analyzes for the observed seismograms from the earthquake swarm induced by the Miyakejima eruption. Spatio-temporal variations in the earthquake source mechanism are found in the seismically active zone, and the three-dimensional attenuation structure in the zone is also derived from the spectral amplitudes of the observed records. The analysis of the seismic motions associated with the caldera collapse indicates slow inflation and some phenomenon represented by a single force beneath the crater.
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