Dynamics of fault gauge during seismic forcal process

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We have investigated the physical properties of gauges samples collected from the crops of several active faults such as the Atotsugawa F., Yanagase F., Gosukebashi F. and Nojima F. The purpose the study is to understand the behavior of gauge under stress field at deep zone. We have carried out some fundamental experiments such as grain-size analysis, lattice strain analysis of the included minerals, measurements of seismic wave velocities and shear strength etc. using gauge samples. Grain-size distribution of common gauge materials is found to a widely from 10 rnm to 1mm under electron microscope. This means that gauge is very compressible under high confining pressure and can be dilatant under shear deformation. The dilatancy will help gauge increase the strength by the strain near the depth of seismic source.The magnitude of lattice strain of quartz and illite minerals were determined using X-ray diffraction analysis and found to be significantly large compared with the same kind of minerals formed in stress-free environment.On the other hand, many clay materials showed electric polarization associated with shear deformation. This phenomenon could not be explained. The mechanism of this Shear-Induced Polarization (SIP) is considered to be related to the physicochemical characteristics of the absorbed water layer contacting the finer grain surface.