A correlation method of apparent velocity measurement

Crustal refraction measurements present many uncertainties, some of which may be resolved by studying the apparent velocities of the entire train of arrivals. Discrete crustal layers have an over-all apparent velocity distribution which is distinctly different from that produced by a major crustal velocity gradient, while travel times show very little difference between the two. Visual measurement of apparent velocities in the secondary portion of a seismogram is uncertain and subject to error due to the lack of sharp onsets of events and to the generally higher background level. A computer method in which velocity filtering and statistical correlation are used has been developed. It eliminates this difficulty and makes it possible to investigate a wide range of apparent velocities. The first results of this method prove it to be a good constraint on a standard interpretation. Also, many features of the travel-time plot are revealed which have yet to be explained. The method promises to be a useful additional tool for the interpretation of crustal refraction measurements.