3-DIMENSIONAL VP AND VP VS STRUCTURE AT LOMA-PRIETA, CALIFORNIA, FROMLOCAL EARTHQUAKE TOMOGRAPHY/

P and S-P times from local earthquakes and P times from explosions at seismic stations in the vicinity of the 1989 Loma Prieta earthquake ar e inverted simultaneously to produce three-dimensional images of Vp an d Vp/Vs structure along the rupture zone. The results confirm the pres ence of the major heterogeneities identified in previous studies using P waves only, including high Vp along the rupture in areas of signifi cant slip and a low-velocity wedge along the San Andreas at the SE edg e of the rupture. A change in rock properties evidenced by a significa nt Vp/Vs increase (equal to a 30% Poisson's ratio increase) from the m iddle crust to the upper crust may have been responsible for the upwar d termination of the main shock rupture. We speculate that the deep hi gh-Vp body that lies along the SE portion of the rupture zone consists of two bodies, based on model results indicating that the SW part of the body has relatively high Vp/Vs while the NE part has relatively lo w Vp/Vs.