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Tanaka, Kiriha*; Muto, Jun*; Nagahama, Hiroyuki*; Oka, Toshitaka
Hoshasen Kagaku (Internet), (110), p.21 - 30, 2020/10
In a fault dating by electron spin resonance (ESR), the number of unpaired electrons trapped in defects in minerals contained in a fault material is detected as ESR intensity. Based on the quantitative change of the intensity before and after an earthquake, the last age of a fault movement can be estimated. However, this method has a hypothesis called "zero-setting" which assumes the decrease in the ESR intensity to zero by fault movement during an earthquake. In order to understand and demonstrate zero-setting, the analysis of the natural fault materials and experiments mimicking fault movements have been conducted. In this paper, we summarized the previous studies about zero-setting by fault movement and described the current status and challenges.
Tanaka, Kiriha*; Nagahama, Hiroyuki*; Muto, Jun*; Oka, Toshitaka; Yabe, Yasuo*
no journal, ,
The mechanisms of the seismic-electromagnetic phenomena attracted as precursors of short-term earthquake forecast have been suggested, however, it is still incompletely understood. Our results showed that the fracture by fault motions could produce the surface charges on the fault. It proves that the electromagnetic abnormalities by the fault motions may also be observed through the surface charging mechanism. Therefore, our study supports that the surface charging mechanism is plausible.
Tanaka, Kiriha*; Muto, Jun*; Takahashi, Miki*; Oka, Toshitaka; Nagahama, Hiroyuki*
no journal, ,
A fault dating using electron spin resonance (ESR) is a method to estimate the age of the last seismic fault activity. This method assumes that natural radiation-induced ESR intensity, which is proportional to trapped charge concentration in the interseismic period, was annihilated by fracture, stress, and frictional heating during the fault slip. However, the sensitivity of ESR can be reduced by high-dielectric materials, we have re-examined the zeroing by seismic fault slips near the surface by performing high-velocity friction experiments and ESR measurements for simulated-fault gouges. Although the decreasing effect of frictional heating on the E
centre is expected, grain fracture affected the centre enough to surpass it, resulting in the increase in the centre with displacements. On the contrary to previous consensus, this implies that seismic fault slips near the surface can increase the E centre due to grain fracture.
center in QuartzTanaka, Kiriha*; Muto, Jun*; Takahashi, Miki*; Jayawickrama, E.*; Sasaki, Osamu*; Oka, Toshitaka; Nagahama, Hiroyuki*
no journal, ,
A fault dating using electron spin resonance (ESR) is a developing direct method to estimate the age of the last fault movement. This method hypothesizes that natural radiation-induced ESR intensity, which is proportional to the concentration of charges trapped in defects accumulated in the interseismic period, is completely reset due to fracture, stress, and frictional heating by a seismic fault slip. The incomplete zeroing can result in age overestimation, hence, the understanding of its detailed conditions and mechanism is required. We have performed high-velocity friction experiments under various normal stresses to investigate the possibility for the signal zeroing by seismic fault slips at various depths. We infer that the degrees of grain fracture and frictional heating associated with the seismic fault slip originating from fault heterogeneity yield the complicated zeroing mechanism of the E center.
Tanaka, Kiriha*; Muto, Jun*; Takahashi, Miki*; Jayawickrama, E. G.*; Sasaki, Osamu*; Oka, Toshitaka; Nagahama, Hiroyuki*
no journal, ,
A fault dating using electron spin resonance (ESR) is a developing direct method to estimate the age of the last fault movement. This method hypothesizes that natural radiation-induced ESR intensity, which is proportional to the concentration of charges trapped in defects accumulated in the interseismic period, is completely reset due to fracture, stress, and frictional heating by a seismic fault slip. We have performed high-velocity friction experiments under various normal stresses to investigate the possibility for the signal zeroing by seismic fault slips at various depths. We infer that the degrees of grain fracture and frictional heating associated with the seismic fault slip originating from fault heterogeneity yield the complicated zeroing mechanism of the ESR signal.