| Project/Area Number |
03402012
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| Research Category |
Grant-in-Aid for General Scientific Research (A)
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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 |
HIRASAWA Tomowo Tohoku Univ., Fac.of Sci., Ass.Prof., 理学部, 教授 (80011568)
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| Co-Investigator(Kenkyū-buntansha) |
KUSUNOSE Kinichiro Geol.Survey J., Senior Scientist, 環境地質部, 課長
KATO Naoyuki Tohoku Univ., Fac.of Sci., Res.Ass., 理学部, 助手 (60224523)
YAMAMOTO Kiyohiko Tohoku Univ., Fac.of Sci., Ass.Prof., 理学部, 助教授 (90004390)
MIURA Satoshi Tohoku Univ., Fac.of Sci., Res.Ass., 理学部, 助手 (70181849)
MISHINA Masaaki Tohoku Univ., Fac.of Sci., Ass.Prof., 理学部, 助教授 (70004421)
堀内 茂木 東北大学, 理学部, 助教授 (00004490)
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| Project Period (FY) |
1991 – 1993
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| Project Status |
Completed (Fiscal Year 1993)
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| Budget Amount *help |
¥12,800,000 (Direct Cost: ¥12,800,000)
Fiscal Year 1993: ¥2,600,000 (Direct Cost: ¥2,600,000)
Fiscal Year 1992: ¥3,300,000 (Direct Cost: ¥3,300,000)
Fiscal Year 1991: ¥6,900,000 (Direct Cost: ¥6,900,000)
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| Keywords | Aseismic Slip / Post-Seismic Faulting / Precursory Slip / Stick-Slip / Nucleation Process / 複合断層 |
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| Research Abstract |
Along the northeastern Japan arc the Pacific plate is subducting beneath the continental plate on which the Japan islands lie. The subduction motion is not uniform either in space or in time. At shallow depths of the boundary between the two plates large earthquakes occasionally take place to produce almost instantaneously a significant amount of slip motion. At large depths, say deeper than 100 km, stable sliding seems to occur at the plate boundary. It may be reasonable to expect that aseismic but episodic slip occurs intermittently at intermediate depths. The present study is thus undertaken to examine the possibility of aseismic slip events propagating at very low speeds in relation to the slip nucleation process.
Laboratory experiments were performed on a rock specimen with a pre-existing fault to generate stick-slip events with various propagation velocities. It is found that slip events with anomalously low propagation velocities are easy to occur on a composite fault made from g
… More
ranite and marble. This suggests the possibility of episodic slip events with very low rupture velocities on the inhomogeneous plate boundary. During the slip-weakening process acoustic emissions are found to be generated supposedly by microfractures of asperities on the fault. Their foci are located inside the slip nucleation zone. This implies that microscopically unstable phenomena (microfractures) are involved in a macroscopically stable phenomenon (stable sliding). In 1992 a large shallow earthquake of low-angle thrust fault type with the magunitude of 6.9 took place at the plate boundary in the region off the coast of Sanriku, Honshu, Japan. Following this shock noticeable post-seismic strain changes were recorded by extensometers at two stations, Miyako and Esashi, which are located near the coast of Sanriku. The observed strain changes are well explained by the model in which aseismic slip with a dacay constant of 12 hours is assumed to take place in the hypocentral region of the main shock. The seismic moment of the aseismic slip is found to be nearly the same as that of the main shock. Less
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