BEHAVIOR OF FRACTURED ZONES AT THE YAMASAKI FAULT FOR TELESEISMIC SURFACE WAVES

Abstract

This paper describes the behavior of fractured zones in the Yamasaki fault by means of analyzing surface waves. The results are as follows: 1) Amplitudes of the strain change caused by surface waves with periods of less than 1 min at the fractured zones are larger than those at the neighboring bedrock. A similar feature was also recognized on the M₂ component of tidal strain (NAKAHORI, 1977). 2) The magnification of strain at the fractured zone is larger in surface waves than in earth tide. 3) The distribution of relative strains along the observation tunnel suggests that the degree of fracturing decreases with the distance from the fractured zones. 4) The Rayleigh wave passing across the fractured zone causes abnormal movements along the fault strike. This feature can be explained by the concept that a slip movement occurs along the fault surface.