Parallelepiped cooling joint and anisotropy of P-wave velocity in the Takidani granitoid, Japan Alps

Correlations between anisotropy of joint systems and physical rock properties, particularly P-wave velocities, were investigated. Characterization of fracture networks in the Takidani granitoid (Japan Alps) was obtained by field observation and laboratory measurement of P-wave velocities. Three preferred joint sets with no shear displacement were identified, and their directions change and spacing progressively increases from the margin to the center of the pluton. The azimuthal variation of P-wave velocity (V_p) is minimal perpendicular to one of the preferred joint orientations. The orientation of microcracks observed at grain scale and joints at outcrop scale show a good correlation. V_p and the preferred orientation of microcracks are in harmony with anisotropy of the joint system, allowing reconstruction of the joint structure in the Takidani granitoid. Thus we were able to evaluate joint anisotropy in terms of V_p anisotropy.