Travel times of P waves from 25 earthquakes to stations in North America, in the distance range 32° to 100°, have been analyzed by a least squares technique similar to the “time term” method of refraction seismology. In this way, deviations from the Jeffreys-Bullen tables have been separated from the effects of station and source. Differences from J-B times were calculated at 2° intervals, and a smooth curve was fitted to the results with an average scatter of 0.07 sec. The station residuals show a marked regional trend, with arrivals up to a second early in the central United States, and up to a second late in the Basin and Range Province. On the assumption that the derived travel time curve is universal in character, station residuals were calculated for stations not in the United States. Although this part of the analysis is less exact, consistent regional trends are apparent. P arrivals are early in shield areas, late in areas of recent tectonic uplift, and early along parts of the Pacific margin where deep-focus earthquakes are common. Station residuals for stations in southern California agree well with those obtained in a study by Press and Biehler. Carder's data from nuclear explosions in the Pacific show broad agreement with the present findings, but discrepancies exist which require further investigation.

First Page Preview

First page PDF preview
You do not currently have access to this article.