Anisotropies of Electrical Conductivities and P Wave Velocities of Cataclasites and Mylonites under Ambient Conditions: Laboratory Measurements of Hatagawa Fault Zone Samples

摘要

1 conducted measurements at ambient conditions of the electrical conductivities and P wave velocities of mylonite and cataclasite samples collected at the Hatagawa fault zone, which is a large exhumed fault in northeastern Japan. Foliations and lineations were clearly observed in the mylonite samples, but no planar or linear fabric was seen on the cataclasite samples. There was little difference in the conductivities at lHz of samples in dry condition. In wet condition, on the other hand, the conductivities of all samples increased by more than one order of magnitude and the conductivities along the three orientations of mylonite were significantly different from each other; the conductivity perpendicular to the foliation is lower by about one order of magnitude. The P wave velocities of the mylonite samples showed anisotropy in both the dry and wet conditions; the velocity perpendicular to the foliation was slowest. The extent of the anisotropy appeared to be small in the wet condition. These results indicate that the distribution and connectivity of cracks in mylonite is anisotropic and that water, which has higher conductivity and lower velocity than the rock matrix, occupies the cracks along the foliation.