An Analysis of the Travel Times of S Waves to North American Stations, in the Distance Range 28 Degrees to 82 Degrees

摘要

The travel times of S waves from 20 earthquakes to stations in North America in the distance range 28 degrees to 82 degrees have been studied. The deviations from J-B times were analyzed into station, source and distance components using the least-squares time-term approach of Cleary and Hales. Station anomalies had a range of about eight seconds, as compared to three seconds for the P anomalies, and are believed to be caused largely by variations in the upper mantle velocity distribution. S residuals, like the P residuals, were generally positive in the western United States, and negative in the central and eastern United States. P and S residuals at the same station correlated with a coefficient of 0.75, the slope of the regression of S anomaly on P anomaly being 3.72. Corrections to J-B times for S were of the order of the standard errors of the determinations. Within the distance range of 28 degrees to 82 degrees large changes of the S velocities, such as were suggested by MacDonald and Ness (1961), are not permitted by the present data. The analysis was checked by carrying out a univariate analysis of variance of the same data. (Author)