2005 Fiscal Year Final Research Report Summary
Research of deformation processes associated with double plate subduction in the Kanto District
| Project/Area Number |
16540384
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Solid earth and planetary physics
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| Research Institution | Nagoya University |
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Principal Investigator |
SAGIYA Takeshi Nagoya University, Graduate School of Environmental Studies, Associate Professor, 大学院・環境学研究科, 助教授 (50362299)
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| Project Period (FY) |
2004 – 2005
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| Keywords | Kanto District / Double plate subduction / Locked zone / Philippine Sea plate / Pacific plate / Postseismic deformation / Kanto earthquake |
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| Research Abstract |
I estimated slip deficit distribution on the plate interface in the Kanto district using a plate configuration model based on large-scale seismic exploration results and microseismicity. The plate interface was estimated as shallower than previous models, and the resultant slip deficit is estimated on the shallower part of the plate boundary of the Philippine Sea plate. The deeper limit of the locked zone is estimated as 15-20km. The shallower locked zone indicates stronger seismic motion in case of large earthquakes, which is an important implication for seismic hazard assessment. Spatial distribution of the locked zone is consistent with the focal region of the 1923 Kanto earthquake. In addition, there is another locked zone southeast off the southern tip of the Boso Peninsula. Rupture of this locked zone may be a crucial factor to distinguish the two types of Kanto earthquake (the 1923-type and the 1703-type).
The subducted Philippine Sea plate contacts the Pacific plate at its bottom. The slip deficit estimated on the Philippine Sea plate is slightly shifted counterclockwise from the relative motion between the NE Japan and the Philippine Sea plate. This difference is attributed to the effect of the Pacific plate subduction. After the 2000 Miyake-Kohzu seismovolcanic event, the crustal deformation pattern in the Kanto district changed. I investigated various possibilities, and concluded that this pattern change was caused by an "afterslip" on the interface between the Philippine Sea plate and the Pacific plate. Such an interplate sliding motion cannot be detected in a usual situation, but I speculate that a tremendous disturbance due to the Miyake-Kohzu event triggered such a rare event.
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