EVALUATION OF THE 3-DIMENSIONAL CONFIGURATION OF A SUBSURFACE ARTIFICIAL FRACTURE BY THE TRIAXIAL SHEAR SHADOW METHOD

We have determined the three-dimensional configuration of a single fracture in the hot dry rock model field at Higashi-Hachimantai, Japan, by the triaxial shear shadow method. The crack was created by hydraulic fracturing in intact welded tuff at a depth of 370 m. We have carried out crosshole seismic measurements by using a downhole air gun and a triaxial seismic detector. Extinction at a special polarization direction and the dependency of transmissivity in shear wave component on incident angle were determined by a triaxial hodogram analysis of detected signals. We have evaluated the orientation and distribution of the fracture using the shear wave extinction, and the three-dimensional configuration of the fracture by a continuation of the evaluated orientations. The results are in good agreement with the data obtained by independent experiments in the field.