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Relative amplitudes of P and S waves as a mantle reconnaissance tool

SEISMOLOGICAL LABORATORY CALIFORNIA INSTITUTE OF TECHNOLOGY, PASADENA, CALIFORNIA

Abstract

The unified magnitude, the ratio of the amiplitudes of S to P waves, and travel-time residuals were compiled from published data for the five Seismological Observatories, TFO, UBO, BMO, WMO and CBO. Using one of the stations as a reference, a relative measure of the above quantities was calculated for each of the other stations for each of a number of earthquakes. The stations in the Basin and Range Province are consistent with a markedly higher attentuation of P waves and a high attenuation of S relative to P when compared to the other stations. This latter observation indicates a high Poisson's ratio in the mantle under the Basin and Range. The delay times to these stations are also consistent with the high Poisson's ratio and with a low-velocity upper mantle. The ratio of the amplitudes of long-period S waves to short-period P waves varies by a factor of 4 among these stations.

BMO, in eastern Oregon, has a high S/P amplitude ratio compared to other stations and a travel-time residual that is comparable to the observatories in the mid-continent. This may be another example of a seismic "window" into the upper mantle that is generated by underthrusting of the oceanic lithosphere.

Footnotes

Now at Esso Production Research Co., Houston, Texas.

This article has been cited by other articles:

				S. C. SOLOMON and M. NAFI TOKSOZ Lateral variation of attenuation of P and S waves beneath the United States Bulletin of the Seismological Society of America, June 1, 1970; 60(3): 819 - 838. [Abstract] [PDF]