Geochronology of paleo-earthquake -dating of fault materials by earthquake-

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This is to date the materials formed during fault movement accomapnied with paleo-earthquakes by K-Ar, Ar-Ar and radiation damage methods after the identification of fault rocks formed by earthquakes.In order to estimate natural radiation level in TL and ESR dating, a portable γ-ray meter was purchased. We also constructed the automated laser step heating system for Ar-Ar dating of single mineral grain.Many structural geologists supported us for sampling of fault rocks, mainly pseudotachlytes from Oshima of Ehime Prefecture and fault gouges from Atotsugawa, Hatagawa, Tasuke and Tanakura systems in Japan, and from MCT in Nepal and Yangsan fault in Korea.Oshima pseudotachlytes and their host metamorphic rocks were dated with the Ar/Ar spot daing method using a pulsed laser. The later results give 100-110Ma for amphiboles and the former, 60-80Ma. The ages of gouges are about 3Ma for the Nepal MCT, 40-50Ma for the Tanakura, 38-46Ma for the Yangson. In the Atotsu system, the ages become younger with decreasing grain size of separates from granites. This tendency is not observed in the separates from sedimentary rocks. However, the ages are about 60Ma.We examined the discordant age relations due to K ion trapped in the expanded layers of smectite When K ion is exchanged by NH4 ion, the ages get 2-5% older than those of the original smectite.We have published more than 20 papers on the results of this project and the related subjects.