Distribution and properties of fractures in and around the Nojima Fault in the Hirabayashi GSJ borehole
H. Ito, T. Kiguchi, 2005. "Distribution and properties of fractures in and around the Nojima Fault in the Hirabayashi GSJ borehole", Petrophysical Properties of Crystalline Rocks, P. K. Harvey, T. S. Brewer, P. A. Pezard, V. A. Petrov
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A borehole penetrating the Nojima Fault was drilled in 1996, one year after the magnitude 7.2 1995 Kobe earthquake. The major fracture distribution detected by a borehole imaging tool (FMI) in the borehole was compared with the S-anisotropy from aftershocks. The fractures far from the Nojima Fault (more than 50 m) are aligned in an east—west direction, that is, parallel to the tectonic stress direction, whereas the fractures close to the Nojima Fault are normal to the fault. In the fault zone, a fault-parallel fault system was observed over short depth intervals, otherwise the fracture system in the fault zone is random. The fault-normal fracture suggests the complete reduction of the shear stress of the Nojima Fault.
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Boreholes are commonly drilled into crystalline rocks to evaluate their suitability for various applications such as waste disposal (including nuclear waste), geothermal energy, hydrology, sequestration of greenhouse gases and for fault analysis. Crystalline rocks include igneous, metamorphic and even some sedimentary rocks. The quantification and understanding of individual rock masses requires extensive modelling and an analysis of various physical and chemical parameters. This volume covers the following aspects of the petrophysical properties of crystalline rocks: fracturing and deformation, oceanic basement studies, permeability and hydrology, and laboratorybased studies. With the growing demands for sustainable and environmentally effective development of the subsurface, the petrophysics of crystalline rocks is becoming an increasingly important field.