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Otani, Tomoyuki*; Kutsuna, Ryosuke*; Kojima, Satoru*; Ohashi, Kiyokazu*; Kakamu, Kazuhiko
no journal, ,
Development of technique in order to judge the activities of fault using chemical characteristics of active faults is useful for the assessment of faults at geological disposal sites. In this study, element transfer at fault gauge was examined. MnO contents were enriched at fault gauge of the Adera and Neodani faults. Most of Mn-bearing minerals are amorphous, it is suggested that Mn-bearing minerals were precipitated from reduced groundwater at oxidized condition when fault gauge were formed.
Shimizu, Mayuko; Ohashi, Kiyokazu*; Niwa, Masakazu
no journal, ,
no abstracts in English
' center by experimental fault slipsTanaka, Kiriha; Ohashi, Kiyokazu*; Muto, Jun*; Oka, Toshitaka
no journal, ,
Electron spin resonance (ESR) dating of a fault assumes that charge trapping centers in quartz in a fault material have been completely annihilated by the seismic fault slip (ESR signal zeroing). There is little understanding of the relationship between the signal zeroing and fault parameters. The previous high-velocity friction (HVF) experiments have implied that the E' center in quartz could be correlated with frictional power density and begin to decrease at a power density of 0.6
0.9 MW/m
. However, the data was lacking to confirm the signal zeroing at higher power density. We performed HVF experiments for simulated quartz gouges with a slip rate of 1 m/s, a displacement of 10 m, and normal stresses of 1.02.5 MPa. ESR measurements were conducted for gouges before and after experiments. The peak-to-peak height of the E' center calibrated by that of the standard material was calculated as the ESR intensity (ESR intensity ratio) of the E' center. The ESR intensity ratio of the E' center decreased with increasing frictional power density of 0.961.4 MW/m. The maximum temperatures near the sliding surface were 260
C at 0.96 MW/m, 600C at 1.0 MW/m, and 480C at 1.6 MW/m. The E' center is thermally unstable at 
300C and more unstable at higher temperatures. Hence, the ESR intensity ratio might decrease due to larger frictional heating with increasing power density. Comparing our results with those in the previous study, the ESR intensity ratio clearly decreased with increasing power densities of 0.61.4 MW/m. HVF experiments mimic seismic fault slips of earthquakes with a moment magnitude of 89 at shallow depths of 
100 m. Seismic fault slip of an earthquake at a depth of at least one hundred meters under the earth's surface can be required for ESR signal zeroing of the E' center.