A search for teleseismic travel‐time anomalies along the San Andreas Fault Zone

Teleseismic arrivals for earth‐quakes occurring in the Tonga Island source region were examined at four stations of the University of California, Berkeley seismographic network to search for local P‐wave velocity variations from 1971 through 1972. The method of two station residuals was used so that only variations in residuals of one station are examined. The difference in two station residuals indicate a generally stable P‐wave velocity and no velocity variation at station LLA associated with the Bear Valley earthquake 23 kilometers from the station. There is also no large variation in P‐wave velocity at station SAO prior to the magnitude 4.9 San Juan Bautista earthquake located 11 km from that station. If P‐wave velocity variations do occur along the San Andreas Fault in central California, our results suggest that an anomalous P‐wave velocity zone would not exceed a radius of 10 kilometers for a magnitude 5 event.