PSconverted waves from large explosions

Autor: Kenneth L. Cook, Joseph J. von Schwind, Joseph W. Berg
Rok vydání: 1960
Předmět:
Zdroj: Journal of Geophysical Research. 65:3817-3824
ISSN: 0148-0227
DOI: 10.1029/jz065i011p03817
Popis: Four seismograms obtained during 1958 and 1959 from large quarry blasts at Promontory (1,221,000 and 2,138,000 Ib of explosive) and Lakeside, Utah (1,500,000 Ib), and the underground Blanca nuclear explosion (38,000,000 Ib equivalent) near Mercury, Nevada, were studied to ascertain whether converted waves of PS type were recorded and, if so, whether they could be used in an analysis of earth crustal layering, as proposed by Andreev in 1957. The PS converted wave is presumed to be composed principally of the SV-type wave (vertically polarized shear wave) and to result from the conversion of energy from the parent compressional P wave at the interface between two crustal layers of contrasting seismic velocity. The method of analysis consisted in computing theoretical times of arrival for PS converted waves based on crustal layering and velocities in the area as determined from refraction seismic studies by Berg, Cook, and Narans [1959], by plotting the radial horizontal component versus the vertical component of velocity of ground motion over appropriate time intervals, and by comparing amplitudes and frequencies of the PS converted waves with the amplitude and frequency of the parent P wave. Arrivals, provisionally interpreted as PS converted waves, were detected on the traces of both the radial horizontal-component seismometers (2 cps natural frequency) and the vertical component seismometers (2 cps). The amplitude of the PS converted waves was usually several times greater than that of the first arrival of the P wave. The successively later arrivals of PS converted waves from successively deeper horizons showed progressively greater ground-velocity amplitudes, as found by Andreev on earthquake seismograms, but some variance from this generalization was found. The frequencies of the various PS converted wave arrivals were approximately the same as those of the parent P wave, between 5 and 10 cps. The crustal layering, which was determined by using the times of arrival of the PS converted waves, compared favorably with that given by Berg, Cook, and Narans for this area. The computed depths of the successive layers were: 5.5, 9.7, 16, and 26 km at Neola, Utah (epicentral distance of about 245 km from Lakeside blast); 12, 26, and 31 km at Gold Hill, Utah (173 km from Promontory); 8.6, 24, and 29 km, also at Gold Hill (379 km from Blanca); and 12, 22, and 31 km at Elko, Nevada (279 km from Promontory).
Databáze: OpenAIRE
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