P AND S TRAVEL TIME ANOMALIES AND THEIR INTERPRETATION
SOUTHWEST CENTER FOR ADVANCED STUDIES DALLAS TX GEOSCIENCES DIV
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Study of the deviations of P and S travel times from the J-B tables at teleseismic distances has shown that there are regional differences in travel time. Both P and S are early in the central and eastern United States, late in the western United States. The differences have a range of about three seconds for P and eight seconds for S. It can be deduced from the relation between the travel time residuals 1 that the change in shear velocity is approximately one and one-quarter times the change in P velocity, 2 that the observations imply a difference in Poissons ratio between the two regions, and 3 that a model in which the shear modulus alone varies, the compressibility remaining sensibly constant, fits the data best. It can be shown also that the differences between the P travel time residuals and the gravity anomalies in the central and western United States are not consistent with the Birch relation between velocity and density.
- Operations Research