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Abstract

The borehole was drilled by the Geological Survey of Japan to penetrate the Nojima fault. The coring, borehole logging and hydrophone VSP experiment were carried out. The fault zone is characterized by altered and deformed rocks from 426.1 m to 746 m, with coaxial zone of fault gouge at 623.3 m to 625.1 m. We detected a few thousands of fractures from FMI images. The trend of the fracture strike at the depth range where the conventional logging data showed extremely anomaly in the fault zone roughly parallel to the surface strike of the Nojima fault, although the strike of all fractures inside of the fault zone is widely dispersed. Seismic anomaly outside of the fault zone estimated from the DSI data is considered to be caused by the aligned fracture with NW - SE trend. It is noteworthy that almost all the resistive fractures are distributed in the shallower depth than the coaxial zone. The strike and dip of some fractures at coaxial zone are consistent with the surface strike of the Nojima fault and the dip estimated from the depth of coaxial zone. The fractures at coaxial zone are considered to be permeable from the results of hydrophone VSP analysis.

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/content/papers/10.3997/2352-8265.20140027
1999-12-15
2021-12-08
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