1988 Fiscal Year Final Research Report Summary
SHORTENING OF FOREARC WEDGE AND BREAKING OF OCEANIC CRUST IN THE SUBDUCTION ZONE
| Project/Area Number |
62490002
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
広領域
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| Research Institution | KOCHI UNIVERSITY |
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Principal Investigator |
KAGAMI Hideo Faculty of Science KOCHI UNIVERSITY ・ PROFESSOR, 理学部, 教授 (50013561)
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| Co-Investigator(Kenkyū-buntansha) |
TOKUYAMA Hidekazu Ocean Research Institute TOKYO UNIVERSITY ASSOCIATE, 海洋研究所, 助手 (10107451)
KODAMA Kazuto Faculty of Science KOCHI UNIVERSITY ・ ASSOCIATE PROFESSOR, 理学部, 助教授 (00153560)
MITUSIO Hiromi Faculty of Science KOCHI UNIVERSITY ・ PROFESSOR, 理学部, 教授 (20036536)
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| Project Period (FY) |
1987 – 1988
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| Keywords | breakdown of oceanic crust / boundary of earthquake rupture zone / Nankaido earthquake in 1964 / New cycle of subduction of PSP / 室戸隆起帯 / 興津隆起帯 / 南海マイクロプレート / 四国山脈の隆起 / 斜め沈み込み運動 / 土佐沈降帯の竜王層群 / 南海道地震 |
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| Research Abstract |
Reconstruction of the geometry of accetionary wedges in the Nankai and Kurile Trenches indicates that the oceanic crust of the sinking slab is always scraped off and incorporated into the accreted wedge. There are observed two types of breakdown of the oceanic crust; the Nankai Trough and Kurile Trench. A depth of 10-15km is the critical boundary to divide the two types into brittle and semi-ductile failures. A Nankai-type failure is characterized by relatively complete rupture of the oceanic crust in the shallow depth causing the heavier wedge.
The Aki canyon fault represents a western boundary of the great earthquakes such as 1964 Nankaido earthquake. The boundary of the rupture zone consists of a broad uplifted zone of muroto peninsula which is characterized by the acute landward tilting of the coastal terrace-surface associated with spray thrust faults. These faults are traced offshore between the Aki and None canyon faults. Fore-arc volcanisms originally existed widespread along the Nankai Trough, however it emerges presently in such an uplifted zone of the rupture boundary alone.
The Okitsu uplifted zone divides Tosa Bay into two seismic faults, eastern part of which is called tosa depression zone. A depocenter of the Ryuo Group at the Tosa depression zone indicated a westward shift with anticlock rotation from that of the underlying tosawan group. An anticlinal axis of the Okitsu uplifted zone also shifted to the same direction, indicating that subduction of the Philippine Sea plate had changed its direction from NNW to WNW since middle pleistocene. This new cycle of subduction along the Nankai Trough causes many geologic events; formation of Nankai microplate, uplifting of the Shikoku coastal mountains, distribution of molasse sediments on land and its equivqlent Ryuo Group at the Tosa depression zone.
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Research Products
(14 results)
