JpGU-AGU Joint Meeting 2017

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[JJ] Oral

S (Solid Earth Sciences) » S-CG Complex & General

[S-CG75] [JJ] Crustal fluids and deformation

Sun. May 21, 2017 1:45 PM - 3:15 PM 106 (International Conference Hall 1F)

convener:Naoji Koizumi(School of Environmental Science,the University of Shiga Prefecture), Koji Umeda(Hirosaki University), Norio Matsumoto(Tectono-Hydrology Research Group, Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology (AIST)), Hidemi Tanaka(School of Science, The University of Tokyo), Chairperson:KOJI UMEDA(Hirosaki University), Chairperson:NAOJI KOIZUMI(School of Environmental Science,the University of Shiga Prefecture)

2:30 PM - 2:45 PM

[SCG75-04] Helium isotope anomalies in the San-in shear zone

★Invited papers

*Koji Umeda1, Koichi Asamori2, Atsushi Saiga2, Takuya NISHIMURA3 (1.Hirosaki University, 2.Japan Atomic Energy Agency, 3.Disaster Prevention Research Institute, Kyoto University)

Keywords:helium isotope, San-in shear zone

A concentration zone of deformation corresponding to the active zone of microseismicity has been identified in an eastern part of the San-in region. This deformed zone, called “ San-in shear zone”, is more than 200 km long along the coast of the Japan Sea and accommodates right-lateral shear motion. Its width is variable, that is, less than 20 km in the eastern part of Tottori Prefecture and 50~70 km in a western part of Tottori Prefecture and the eastern part of Shimane Prefecture. Elevated 3He/4He ratios in groundwaters sampled from hot spring and drinking water wells are observed around the shear zone, suggesting the emission of mantle-derived helium. The deformation may be attributed to the low viscosity in the crust because the concentrated supply of mantle fluids with high 3He/4He ratios may weaken the lower crust.