| Project/Area Number |
02041031
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| Research Category |
Grant-in-Aid for international Scientific Research
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| Allocation Type | Single-year Grants |
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| Section | Field Research |
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| Research Institution | Yokohama National University |
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Principal Investigator |
OTA Yoko Department of Geography. Yokohama National University, 教育学部, 教授 (80017714)
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| Co-Investigator(Kenkyū-buntansha) |
JOSE Naranjo チリー地質調査所, 研究員
ALAN Nelson アメリカ合衆国地質調査所, 研究員
KOBA Motoharu Department of Geopgraphy, Kansai University, 文学部, 助教授 (40141949)
MATSUSHIMA Yoshiaki Kanagawa Prefectural Museum, 専門学芸員 (20124521)
UMITSU Masatomo Department of Geography, Nagoya University, 文学部, 助教授 (50127883)
NELSON Alan R. United States Geological Survey
NARANJO Jose A. Servicio Nacionale de Geologia y Mineria, Chile
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| Project Period (FY) |
1990
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| Project Status |
Completed (Fiscal Year 1990)
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| Budget Amount *help |
¥3,000,000 (Direct Cost: ¥3,000,000)
Fiscal Year 1990: ¥3,000,000 (Direct Cost: ¥3,000,000)
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| Keywords | Buried peat bed / Paleoseismicity / Late Quaternary seismo-tectonics / Western coast of USA / Chile / Plate boundary / Marine terrace / Active fault |
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| Research Abstract |
This study aims to establish the late Quaternary seismo-tectonic movement in the Circum Pacific area. Field work was carried out in 1990 in the western coast of USA and in the coastal area of northern Chile. Results are summarized as follows :
Western coast of USA : Naselle River mouth. Washington : At least one buried forest and two buried peat beds were found on the bank of the Naselle River mouth. 14C ages for them are ca. 600, 1540, and 2100 yr BP, from the top to the bottom. These dates are consistent with those known in the other southern Washington and support that episodic submergence over an extensive area have been repeated during the late Holocene, probably related to the subduction of Juan de Fuka Plate.
South Slough. Oregon : Holocene sediments of eight tributaries of South Slough, Which is located on a synclinal axis, were excavated. At least five buried peat beds are commonly found from most of excavated sites. Diatom analysis shows the repeated occurrence of fresh water e
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nvironment and brakisch water environment. Sulpher content also changes with different environments. These imply that the growth of a local synclinal structure possibly has occurred episodically (coseismically).
Coastal area of northern Chile : 1) TLD Element. which is necessary for the ESR dating and was buried in the soil in 1989 at about 30 localities, was collected, and shells samples from marine terraces will be determined by ESR dating soon. 2) All the faults in the Mejillones Peninsula are proved to be normal faults by this study. Active faults can be classified into three categories, that is, main boundary faults, subsidary faults in the uplifting area and subsidary faults in lowlands. Nature of these faults are confirmed by detailed mapping and observation of faults. 3) Relation between marine terraces and structure of underlying Tertiary rocks is confirmed. Age of the oldest marine terrace in this area probably dates back to sometime of Pliocene or even Miocene. 4) Uplift rate in this area seems to be very slow. The presence of normal faults and such a slow uplift in the northern coast gives a significant difference in the behavior at plate boundary between the subduction zones in the western Pacific and the Pacific coast of Chile. This study constraints a nature of the plate boundary and the study area is regarded to have been a tensional stress field during the Quaternary. Less
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