SHEAR-WAVE POLARIZATION ALIGNMENTS RECORDED ABOVE THE KAOIKI FAULT ZONE, HAWAII

Eighty-four shear wave records from the seismometer station AIN at Kaoiki, Hawaii, covering the years 1979-1983, were examined for the presence of shear wave splitting and possible precursory change associated with a mainshock in 1983. Time-delayed arrivals with different polarizations were detected, suggestive of shear-wave splitting, and the polarizations of the first-arriving shear waves were aligned in the direction ESE-WNW. This direction is consistent with the anisotropy being caused by cracks aligned approximately perpendicular to the direction of least principal stress, which is uniform over the ray path in an otherwise heterogeneous stress field. No time-dependent variation of the polarization of the leading split shear-wave was observed. Investigation of temporal variation of time delays between split shear-waves was not possible due to the presence of scattered arrivals.