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Surface-wave attenuation and crustal anelasticity in Central North America

Mitchell, Brian J. (1973) Surface-wave attenuation and crustal anelasticity in Central North America. Bulletin of the Seismological Society of America, 63 (3). pp. 1057-1071. ISSN 0037-1106.

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The southeastern Missouri earthquake of October 21, 1965 generated fundamental- and higher-mode Love and Rayleigh waves which were recorded at numerous North American stations. Love-wave amplitude radiation patterns were determined and found to be consistent with theoretical patterns predicted by a fault-plane solution previously inferred from Rayleigh-wave data. The radiation patterns were used to estimate the source spectrum and values for Love-wave attenuation coefficients for the mid-continent of North America by a least-squares iterative process. The source spectrum derived from Love-wave amplitudes exhibits a peak at periods between 5 and 9 sec and decreases to a lower DC level at longer periods, in agreement with the source spectrum determined previously for Rayleigh waves. The Love-wave attenuation coefficients decrease rapidly from about 0.0018 km^(−1) at a period of 4 sec to about 0.0001 km^(−1) at a period of 20 sec. At periods between 20 and 40 sec the values seem to remain nearly constant. The crust in the mid-continent of North America is characterized by relatively low Q_β values, 75 to 300, in its upper portion. At depths between 15 and 20 km, Q_β increases sharply and decreases again at greater depths. The decrease can be explained as being due to increasing temperature in a homogeneous material, but the sharp increase requires a change in the chemical constitution of the material at mid-crustal depths.

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Additional Information:Copyright © 1973, by the Seismological Society of America. Manuscript received November 21, 1972. I am grateful to Drs. Don L. Anderson, Charles B. Archambeau, David G. Harkrider, Donald V. Helmberger, and to Mr. Ralph W. Alewine for helpful discussions on aspects of this paper. Dr. Harkrider permitted me to use his suite of surface-wave computation programs, Dr. Adam Dziewonski provided me with a copy of his multiple filter program, and Mr. Alewine allowed me to use an adaptation of his inversion program for this study. The program for rotating digitized seismograms used in this study was written by Mr. James H. Whitcomb. Dr. William Stauder furnished seismograms recorded by the St. Louis University network. Dr. Anderson, Dr. Harkrider, and Mr. Alewine critically read the manuscript. This research was supported by the Advanced Research Projects Agency of the Department of Defense and was monitored by the Air Force Office of Scientific Research under Contract F44620-72-C-0078.
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Advanced Research Projects Agency (ARPA)UNSPECIFIED
Air Force Office of Scientific Research (AFOSR)F44620-72-C-0078
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Caltech Division of Geological and Planetary Sciences2247
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ID Code:48526
Deposited By: George Porter
Deposited On:14 Aug 2014 15:35
Last Modified:03 Oct 2019 07:04

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