Three-dimensional Q-1 variations in the aftershock region of Loma Prieta are derived by tomographic inversion. Low Q is observed near the surface and Q generally increases with depth. The southwest side of the San Andreas fault exhibits lower Q than does the northeast side and this feature apparently extends to approximately 7 km depth. The fault zone, as determined by the dipping plane of aftershock activity, is characterized by slightly higher Qp and lower Qs, compared to regions immediately adjacent to the fault. These correlate with high-velocity anomalies associated with seismicity at depth
