Abstract

Travel times for shear waves in a layer of granite have been computed on the basis of recent laboratory work which permits an approximate evaluation of the variation of velocity with depth. The results are found to agree very closely with those of Leet, found by the method of timed blasts, for New England. The mean surface velocity of shear waves in granite having their focus at the surface is computed to be 3.52 km/sec. at 568 km., decreasing to 3.26 at 25 km.; the curvature is shown to be too small to be easily recognized from records of near earthquakes. A depth of 15 km. for the granitic layer is shown to be consistent with Leet's observations of pulses through a second layer.

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