OBSERVATIONS OF SHEAR-WAVE SPLITTING ON THE SOUTHEAST FLANK OF MAUNA-LOA VOLCANO, HAWAII

We use a combination of particle motion covariance matrix decompositio n, particle motion plots, and cross correlation to estimate the polari zation and split times of shear wave arrivals from local earthquakes i n the Kaoiki and Hilea regions of southern Hawaii. Consistent leading shear wave polarizations and identifiable fast and slow shear wave arr ivals were frequently observed. Average delay times for the four array s vary from 100 to 230 ms. The leading shear wave polarizations at sta tions in the Kaoiki region agree with the direction of the local maxim um horizontal compressive stress, sigma(H), determined from focal mech anism studies and field observations of ground rupture. For the Bird P ark (BP) array, in the Kaoiki region, the relationship between delay t ime and event depth shows evidence for both dominant shallow and weake r pervasive anisotropy. The correlation between delays and event depth is much weaker for the Ainapo (AN) array than for BP, however a small er slope is apparent. Conservative estimates of the crack densities fo r the BP and AN arrays are e = 12% and e = 6%, respectively. In the Hi lea region, the leading shear wave polarization for the Punaluu Gulch (PG) array differs by approximately 30-degrees from the direction Of s igma(H) determined from focal mechanism studies, while the Waihaka Gul ch (WG) array shows no predominant polarization direction. No correlat ion between delay time and event depth was observed for either of the two Hilea arrays.