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Seismological Aspects of the Guatemala Earthquake of February 4, 1976

Kanamori, Hiroo and Stewart, Gordon S. (1978) Seismological Aspects of the Guatemala Earthquake of February 4, 1976. Journal of Geophysical Research B, 83 (B7). pp. 3427-3434. ISSN 0148-0227. doi:10.1029/JB083iB07p03427.

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Detailed analyses of teleseismic surface waves and body waves from the Guatemala earthquake of February 4, 1976, show the following: (1) Left lateral displacement along a vertical fault with a strike varying from N66°E to N98°E is consistent with the teleseismic data. (2) The seismic moment was 2.6 × 10^27 dyn cm. The directivity of the surface wave radiation indicates an asymmetric (1:2.3) bilateral faulting with a total length of 250 km. In modeling the displacement a rupture velocity of 3 km/s was used, and the fault curvature was included. (3) If a fault width of 15 km is assumed, the average offset is estimated to be about 2 m. This value is about twice as large as the average surface offset. (4) Although the observed directivity suggests a uniform overall displacement along the fault, the body wave analysis suggests that the earthquake consists of as many as 10 independent events, each having a seismic moment of 1.3–5.3 × 10^26 dyn cm and a fault length of about 10 km. The spatial separation of these events varies from 14 to 40 km. This multiple-shock sequence suggests that the rupture propagation is jagged and partially incoherent with an average velocity of 2 km/s. (5) The average stress drop estimated from surface waves is about 30 bars, but the local stress drop for the individual events may be significantly higher than this. (6) The complex multiple event is a manifestation of a heterogeneous distribution of the mechanical properties along the fault, which may be caused by either asperities, differences in strength, differences in pore pressure, differences in slip characteristics (stable sliding versus stick slip), or combinations of these factors. (7) This complexity has important bearing on the state of stress along transform faults and is important in assessing the effect of large earthquakes along other transform faults like the San Andreas.

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Kanamori, Hiroo0000-0001-8219-9428
Additional Information:This paper is not subject to U.S. copyright. Published in 1978 by the American Geophysical Union. Received April 19, 1977; revised November 18, 1977; accepted February 24, 1978. Paper number 8B0225. We would like to thank the personnel of all the WWSSN stations who were kind enough to send us seismograms. We also thank George Plafker for useful discussions and A. F. Espinosa for an advance copy of U.S. Geological Survey Professional Paper 1002 (1976). This research was supported by a grant from the National Academy of Sciences, through WDC-A for seismology; the Division of Earth Sciences, by National Science Foundation grant (EAR76-14262); and by U.S. Geological Survey contracts 14-08-0001-15893 and 14-08-0001-16776. Contribution 2901, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125.
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National Academy of SciencesUNSPECIFIED
NSFEAR 76-14262
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Caltech Division of Geological and Planetary Sciences2901
Issue or Number:B7
Record Number:CaltechAUTHORS:20150708-140136098
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Official Citation:Kanamori, H., & Stewart, G. S. (1978). Seismological aspects of the Guatemala Earthquake of February 4, 1976. Journal of Geophysical Research: Solid Earth, 83(B7), 3427-3434. doi: 10.1029/JB083iB07p03427
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:58812
Deposited On:10 Jul 2015 14:51
Last Modified:10 Nov 2021 22:10

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