Abstract
We attempt to detect the lineament structure inside the crust using a shear-wave splitting analysis. A seismicity map suggests several lineaments in southwest Japan. No clear active fault was found to support the lineaments. We researched shear-wave splitting in southwest Japan using two later phases: PpPms and PpSms. The PpPms is a later S-phase, which is reflected at the surface as a P wave, dives again, and reflected and converted from P to S at the Moho boundary. The PpSms is a later arriving S-phase, which is converted from P at the Earth's surface, and is reflected at the Moho discontinuity before arriving at a seismic station. The PpPms and PpSms phases are used to detect lineament structures inside the crust. The observed polarization directions obtained are ENE-WSW, NE-SW, and N-S with a lateral variation. The directions are not consistent with that of maximum principal stress in the area. The results of shear-wave splitting in southwest Japan could not be explained by crack-induced anisotropy caused by maximum principal stress. The direction NE-SW is consistent with that of the geological lineament structure in this area. The shear-wave splitting is probably caused by the lineament structure inside the crust.
