Revised travel times in southern California*

Abstract

Discrepancies of up to 20 per cent between wave velocities calculated from blast records in southern California and those found from earthquakes necessitate a reinterpretation of seismograms of all near-by shocks and a revision of travel-time curves. A combination of findings for S — P intervals as a function of distance in southern California earthquake records with the ratio of mean interval velocities for P and S waves shows (without assumption of origin times) that the mean velocities of the two waves between the source and the surface are about 6.35 and 3.67 km/sec., respectively. This agrees with the results found from blast records. Most revised origin times are between ¾ sec. and 1 1/2 sec. later than those found previously from P¯. The method applied here removes the difference in origin time for longitudinal and transverse waves which was found formerly for earthquakes. Travel-time curves of various phases are revised and reinterpreted. The change in amplitudes with distance of several wave types is discussed.