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Oral presentation

An Attempt to estimate the migration process of deep fluid using S-wave splitting analysis

Hiratsuka, Shinya; Saiga, Atsushi; Asamori, Koichi

no journal, , 

Hydrothermal activity is generated in the Kii Peninsula although it is a non-volcanic region. High helium isotope ratio, low seismic velocity and low resistivity suggest that hydrothermal water is originated from deep fluid. This study attempt to estimate the migration process of deep fluid using seismological method so-called S-wave splitting analysis. The result shows that high anisotropic region may correspond to migration process of deep fluid, but it is necessary for more accumulation of seismological data.

Oral presentation

An Attempt to estimate the migration pathway of slab-derived fluid using shear wave splitting analysis

Hiratsuka, Shinya; Asamori, Koichi; Saiga, Atsushi

no journal, , 

no abstracts in English

Oral presentation

Visualization of crustal deformation in a high-strain shear zone by geodetic, geomorphologic, and geologic approaches

Niwa, Masakazu; Shimada, Koji; Watanabe, Tsuyoshi; Goto, Akira; Hiratsuka, Shinya

no journal, , 

As a case study to visualize crustal deformation induced by concealed faults and related structures, we applied integrated approaches of geodesy, geomorphology, and geology to a high-strain shear zone in southern Kyushu, Japan. Our GNSS observation for recent 4.7 years by a network composed of 10 stations revealed that locking depth and slip velocity of the deeper extension of the fault were estimated to be 8 km and left-lateral slip of 9 mm/year. In the geomorphological approach, concentration of E-W trend lineaments is identified in northwestern Kagoshima, near the center of the sinistral high-strain shear zone detected by the GNSS observation. The field survey showed that minor faults are common in the study area. Thus, we analyzed stress field estimated from slip data of the minor faults, and compared it with the stress field corresponding to the sinistral high-strain shear zone. The result of the analysis suggests that the subsurface deformation due to the sinistral high-strain shear zone is localized rather than dispersed.

Oral presentation

Shear wave splitting analysis for the crust in Iwaki area, Fukushima Prefecture, northeast Japan

Watanabe, Tsuyoshi; Hiratsuka, Shinya*; Shimada, Koji

no journal, , 

Fluid has a significant influence on the seismogenic process because it reduces the fracture strength of rocks. Fluid migration also affects the long-term safe confinement function of a geological disposal systems. To clarify the existence and the migration channels of such fluid, shear wave splitting analysis is a useful method, which can estimate the anisotropy related to cracks and fluid in the crust. We conducted the shear wave splitting analysis in Iwaki area, northeast Japan, where seismic activity was increased and anomalous discharge of hot springs was observed about one month after the 2011 Tohoku Earthquake (Mw 9.0). As a result, we showed that the crack orientations turn to generally arc-parallel direction in Iwaki area, and additionally, that the spatial distribution of anisotropic intensity is relatively high at a seismic site near the hot springs with anomalous discharge. This suggests that fluid from deep underground gather in the crust in steady-state.

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