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Regional variations of source properties in southern California estimated from the ratio of short- to long-period amplitudes

Wyss, Max and Brune, James N. (1971) Regional variations of source properties in southern California estimated from the ratio of short- to long-period amplitudes. Bulletin of the Seismological Society of America, 61 (5). pp. 1153-1167. ISSN 0037-1106.

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The ratio of short- to long-period amplitude is expressed in terms of apparent stress, rigidity times energy over moment (μE_G/M_0), for 277 earthquakes in California. A map showing the apparent stresses is compiled. In general, the Mendocino and San Andreas faults as well as the Gulf of California area are regions of large surface-wave excitation and little short-period radiation (low apparent stress). Away from the main fault zones, the apparent stresses tend to be higher. Regions of conspicuously low surface-wave excitation (high apparent stress) are the Laguna Salada-Sierra Juarez region in northern Baja California, the California-Nevada border region north of Bishop, and the region associated with the bend of the San Andreas between San Bernardino and San Gorgonio Mountain. A detailed comparison of earthquakes with accurately-known depths at Parkfield and Borrego Mountain indicates two important differences in apparent stresses between these two source regions. The apparent stress at all depths is larger at Borrego Mountain than at Parkfield, and it increases with depth at Borrego Mountain, whereas it remains constant at all depths at Parkfield. The explanation for the variation of surface-wave excitation (apparent stress) is not known for certain, but it could be related to variations in true stress.

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Additional Information:Copyright © 1971, by the Seismological Society of America. Manuscript received November 23, 1970. Most of this research was carried out while the authors were associated with the California Institute of Technology. The extensive and helpful critical comments by Dr. C. R. Allen which lead to substantial improvement of the manuscript are gratefully acknowledged. The authors wish to thank Dr. P. Molnar, Dr. B. Isacks, and Dr. L. Sykes who read the manuscript and made many helpful comments. This research was supported by National Science Foundation grant NSF-GA-12868 and NSF-GA-22709.
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Caltech Division of Geological Sciences1949
Issue or Number:5
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:48870
Deposited By: George Porter
Deposited On:26 Aug 2014 14:32
Last Modified:03 Oct 2019 07:08

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