2000 Fiscal Year Final Research Report Summary
Seismo-Tectonic Studies on Split Subduction of the Steeply Dipping Plate
| Project/Area Number |
09440161
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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 |
固体地球物理学
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| Research Institution | Kagoshima University |
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Principal Investigator |
KAKUTA Toshiki Kagoshima University, Faculty of Science, Professor, 理学部, 教授 (40041222)
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| Co-Investigator(Kenkyū-buntansha) |
YAKIWARA Hiroshi Kagoshima University, Faculty of Science, Research Associate, 理学部, 助手 (60295235)
MIYAMACHI Hiroki Kagoshima University, Faculty of Science, Associate Professor, 理学部, 助教授 (30182041)
GOTO Kazuhiko Kagoshima University, Faculty of Science, Associate Professor, 理学部, 助教授 (20244220)
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| Project Period (FY) |
1997 – 2000
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| Keywords | split subduction / left-lateral strike slip / narrow seismic zone / block boundary of seismicity / Tokara submarine canyon / mantle wedge / Amami Oshima / OBS observation |
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| Research Abstract |
The 1997 Northwestern Kagoshima Earthquakes (M6.5, 6.3) suggest a left-lateral strike slip movement due to subduction of the Philippine Sea plate splitted into several blocks ; they occurred in a narrow seismic zone through the crust in South Kyushu with a strike of nearly E-W and a block boundary of seismicity is found on the east extension of the zone in a region of Hyuganada. It is probably another evidence that westward migration of swarm type earthquakes was observed along the zone from January through July, 1995. Then we investigated especially crustal structures along the seismic zone on land and west off Kyushu.
Seismic activity in and around the Tokara submarine canyon, north off Amami Oshima, Ryukyu islands was investigated in detail by deploying not only OBS's but also temporary stations, because a left-lateral tectonic line is geologically supposed along the canyon and because dip angles of the subducting plate are iferred to differ largely on the both sides with each other. From the temporary observation in Amami Oshima, we found crustal earthquakes at depths of 11 to 19km and active earthquakes in a mantle wedge where any earthquakes have never been found in Kyushu except the east region off Tanegashima island. The subducting plate is also estimated at depths of 40-50 km with a low dip angle of about 25° under the island. From the observation of 10 OBS's and 9 land stations deployed aroud the Tokara submarine canyon, any clear difference was, however, not found in dip angle between both sides of the canyon, although some clusters of crustal and intraplate earthquakes were found along the canyon.
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