Development of a geochemical and petrological method for retrieving records of thermal pressurization occurred in the seismic faults

2015 Fiscal Year Final Research Report

• Project/Area Number: 24340127
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Partial Multi-year Fund
• Section: 一般
• Research Field: Geology
• Research Institution: Japan Agency for Marine-Earth Science and Technology
• Principal Investigator: ISHIKAWA Tsuyoshi 国立研究開発法人海洋研究開発機構, 高知コア研究所, 研究所長 (30270979)
• Co-Investigator(Renkei-kenkyūsha): HIRONO Tetsuro 大阪大学, 大学院理学研究科, 准教授 (70371713)
• Project Period (FY): 2012-04-01 – 2016-03-31
• Keywords: 自然災害 / 地震 / 地球化学 / 地質学 / 断層

Outline of Final Research Achievements

For assessing whether the faults experienced thermal pressurization (TP), which may lead to a marked reduction in fault strength during seismic slip, the validity of geochemical and petrological analyses of fault rocks was examined. Chemical analyses for the deformed rocks from a fossil plate-boundary fault in the Kodiak accretionary complex, USA, and from an active fault of the Median Tectonic Line in the Nagano area, Japan, revealed occurrence of coseismic fluid-rock interactions at high temperatures (250 to >350 deg. C) required for TP. Frictional experimental works also demonstrated that coseismic interactions with high-temperature fluids can produce detectable chemical anomaly in the fault rocks. At the temperatures higher than 300 deg. C, chemical anomaly observed in the fault rocks is consistent with that predicted by model calculation, indicating that the present method is useful for evaluating coseismic physicochemical processes in the fault, including TP.

Free Research Field

地球化学・岩石学