2003 Fiscal Year Final Research Report Summary
Short-term variation and history of cold seep activity along active faults off Tokai
| Project/Area Number |
13440144
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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 |
Geology
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| Research Institution | The University of Tokyo |
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Principal Investigator |
ASHI Juichiro The University of Tokyo, Ocean Research Institute, associate professor, 海洋研究所, 助教授 (40251409)
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| Co-Investigator(Kenkyū-buntansha) |
KINOSHITA Masataka JAMSTEC, DSR, Associate Scientist, 深海研究部, 副主幹 (50225009)
TOKUYAMA Hidekazu The University of Tokyo, Ocean Research Institute, professor, 海洋研究所, 教授 (10107451)
MATSUMOTO Ryo The University of Tokyo, Graduate School of Science, professor, 大学院・理学系研究科, 教授 (40011762)
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| Project Period (FY) |
2001 – 2003
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| Keywords | gamma-ray / active fault / Nankai Trough / Off Tokai region / cold seepage / accretionary prism / accretionary / sediment / Uranium series radionuclide |
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| Research Abstract |
A large number of sea bottom gamma ray data have been obtained using JAMSTEC submersibles and ROVs, and have been discussed about relations to geological background. However, γ -ray spectrometers attached with the submersible or vehicle are affected by relatively short measurement time and seafloor disturbance during landing and taking-off. We developed a stand-alone system of gamma ray measurement, named GRAMS (Gamma Ray Monitoring System) and tested it in the Sagami Bay. Total intensity of gamma ray and radionuclide contents monitored for about two days are relatively constant and show no periodic variation. We carried out GRAMS to know spatial distribution of gamma ray along the out-of-sequence thrust in the central Nankai accretionary prism. It is evident that total intensity of gamma ray and radionuclide contents of Th-series and U-series at cold seep sites are higher than those at normal seafloor. Twenty-two day's records of gamma ray monitoring by GRAMS show very high intensity and high anomaly of U-series radionuclide at the seep site. However, all values show no fluctuation with time. This suggests that gamma ray is not sensitive to seep itself but attributed to accumulation of radionuclide, probably derived from damaged rock of the fault zone, within surface sediments.
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[Publications] Juichiro ASHI, Kan AOIKE, Yasuyuki NAKAMURA, Saneatsu SAITO, Shin'ichi KURAMOTO, Masataka, KINOSHITA, Sumito MORITA, Urumu TSUNOGAI, Shigeaki KOJIMA, Pierre HENRY: "Geological Structure and Cold Seep at the Daini-Atsumi Knoll off Enshu-Nada"JAMSTEC Journal of Deep Sea Research. 24. 1-11 (2004)
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