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Determination of crustal structure from phase velocity of Rayleigh waves. Part II: San Francisco Bay region

Press, Frank (1957) Determination of crustal structure from phase velocity of Rayleigh waves. Part II: San Francisco Bay region. Bulletin of the Seismological Society of America, 47 (2). pp. 87-88. ISSN 0037-1106.

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The phase velocity method of measuring crustal thickness has been successfully applied in southern California. Phase velocity of dispersed Rayleigh waves from distant earthquakes is determined locally by use of a tripartite array of seismograph stations. Local crustal thickness is obtained by comparing the observed phase velocity with an experimentally determined curve representative of the average continental crust. In this paper we make use of the phase-velocity data of Evernden to determine crustal thickness in the San Francisco Bay region of California. Evernden determined the phase velocity of Rayleigh waves entering the North American continent from the Pacific Ocean. He was primarily interested in studying the direction of approach of these waves. His tripartite array consisted of stations at Berkeley, San Francisco, and Palo Alto, and a number of earthquakes were studied so that a large variation in direction of approach could be obtained. The data for all the earthquakes were combined to obtain an average phase velocity for each period. These phase velocities are plotted in figure 1, where the region to which the data apply is also shown. Also plotted in figure 1 are phase-velocity curves for a 25-km., 35-km., and 45-km. crust having the same composition as the average crust of Africa. The method by which these curves have been derived is explained in Part I (see fn. 1, above). By interpolating between the curves one can use each phase-velocity determination to obtain a value of crustal thickness. Neglecting the lowest three points which fall outside the range permitted by the phase-velocity curves, one finds a mean value of 30 ± 1 km. for crustal thickness in the San Francisco Bay region. The three points which were excluded fall in a period range where experimental phase-velocity determinations are difficult to make. Moreover, for these short periods the phase velocity for the oceanic segment of the path differs greatly from that for the continental segment, with the result that refraction effects are most pronounced.

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Additional Information:Copyright © 1957, by the Seismological Society of America. Manuscript received for publication July 26, 1956.
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Caltech Division of Geological Sciences822
Issue or Number:2
Record Number:CaltechAUTHORS:20140805-163908584
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:48028
Deposited By: George Porter
Deposited On:06 Aug 2014 15:22
Last Modified:03 Oct 2019 06:59

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