Evidence for rapid fault healing derived from temporal changes in S wave splitting

Abstract

Tadokoro et al. [1999] had made an S wave splitting analysis on the Nojima fault zone that ruptured during the 1995 Hyogo-ken Nanbu earthquake for a period 9-12 months after the mainshock. The direction of faster shear wave polarization φ had been parallel to the fault strike, suggesting fractures of shear fault origin. In this study, we made an additional S wave splitting analysis for a period 33-45 months after the mainshock and detected the rotation of φ, that is, the direction φ was parallel to the regional maximum horizontal compressional stress which is oblique to the fault strike. This temporal change suggests that all the fractures of shear fault origin had completely healed and cracks of tectonic stress origin recovered between the two periods. This is strong evidence for rapid fault healing which completed within 33 months after the mainshock.