1997 Fiscal Year Final Research Report Summary
Crustal heterogeneity around active faults and volcanoes in southwestern part of Japan-Inversion analysis of coda envelopes-
| Project/Area Number |
07804028
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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 |
固体地球物理学
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| Research Institution | KYOTO UNIVERSITY |
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Principal Investigator |
NISHIGAMI Kinya Kyoto University, Disaster Prevention Research Institute, Associate Professor, 防災研究所, 助教授 (00189276)
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| Project Period (FY) |
1995 – 1997
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| Keywords | scattering / tomography / active fault / crustal structuve / crustal heterogeneity / coda waves / reflector |
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| Research Abstract |
The inversion analysis method of coda envelopes was applied to several active fault regions and also active volcano regions that include Fukui-earthquake fault, Nojima fault, Rokko fault system, Yamasaki fault system, Mt.Ontake, Mt.Hakusan, and Mt.Nikko-Shirane. Through estimating the 3-D distribution of coda scatterers, the following characteristics of crustal heterogeneities are obtained : (1)Strong scatterers exist at 10-20 km depth below active volcanoes and the scatters are interpreted as S wave reflectors. (2)The distribution of reflectors is obtained in more detail than usual reflection analyzes. (3)A vertical distribution of scatterers is also estimated at 0-7 km depth below Mt.Ontake. (4)Strong scatterers exist along active faults at depths of 0-20 km. (5)A low seismicity area near the Fukui-earthquake fault well correlates to a weak scattering region. (6)Strong scattering zone are estimated at depths of 20-30 km just below the fault plane of the 1995 Hyogo-ken Nanbu earthquake (M7.2). This zone may correspond to the lower crust in this area. (7)The strongest heterogeneity in the above stated scattering zone is located close to the hypocenter of the 1995 Hyogo-ken Nanbu earthquake.
This study has revealed several meaningful heterogeneous structures around active faults and volcanoes. Crustal heterogeneity is supposed to be strongly related to the occurrence of major earthquakes as shown in (6) and (7) above, and further investigation of crustal heterogeneities through this kind of inversion analysis will be necessary.
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