| Co-Investigator(Kenkyū-buntansha) |
UMINO Norihito Tohoku University, Graduate school of Science, Professor, 大学院理学研究科, 教授 (30004477)
MATSUZAWA Toru Tohoku University, Graduate school of Science, Associate Professor, 大学院理学研究科, 助教授 (20190449)
MIURA Satoshi Tohoku University, Graduate school of Science, Associate Professor, 大学院理学研究科, 助教授 (70181849)
OKADA Tomomi Tohoku University, Graduate school of Science, Associate Professor, 大学院理学研究科, 助教授 (30281968)
YABE Yasuo Tohoku University, Graduate school of Science, Assistant Professor, 大学院理学研究科, 助手 (30292197)
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| Research Abstract |
In this research, we have been aiming to analyze details of lock and slip on the plate boundary under the Pacific Ocean in NE Japan and to understand the generation mechanism of interplate earthquakes. The main research contents are: 1. analysis of repeating earthquakes, 2. analysis of source process of medium ＆ large earthquakes based on broadband seismic waveform data, 3. GPS data analysis, 4. research on the property of asperities by using numerical simulation.
According to the result of 1. analysis of repeating earthquakes, we successfully estimated the time variation of interplate slips around the rupture zone of the 2003 Tokachi-oki earthquake, by identifying the repeating earthquakes in all parts of the plate boundary under the Pacific Ocean from Hokkaido to NE Japan. As for the 2. analysis of source process based on seismic waveform data, we showed that the rupture area of Miyagi-oki earthquake (M7.2) on Aug. 16, 2005 is overlapped with the southeastern part of the rupture area
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of the 1978 Miyagi-oki earthquake. So, this means that the asperities of the 1978 earthquake located in the north and west part are left unruptured; our research pointed out the importance of continued and careful observation on this area. Moreover, we conducted reanalysis of aftershocks of Miyagi-oki earthquakes with magnitude >7 in 1930s, and found out that three asperities could have slipped separately, in three times, in the case of 1930s' Miyagi-oki earthquakes. With 3. GPS analysis, after 2005 Miyagi-oki earthquake, we detected the after slip which spread toward south of the rupture area of the event. This observation result corresponds with the result of seismic-waveform inversion analysis; the northern and western asperities are left unruptured. The result of 4. numerical simulation analysis shows that, in order to explain the propagation velocity of the after slip observed in the deep plate boundary close to land, pore pressure around the plate boundary should be extremely large. On the other hand, in order to explain the propagation velocity of the after slip observed in the shallow plate boundary close to the trench, large pore pressure is not necessary like in the case above. These results suggest the depth variation in the amount of water supplied to the plate boundary, which was caused by dehydration reaction, or the depth variation in coefficient of permeability around the plate boundary.
As mentioned above, through this research, we have achieved substantial results to enhance understanding of the generation mechanism of interplate earthquakes. Less
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