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Seismicity patterns (1963-1983) as stress indicators in the Shumagin seismic gap, Alaska

Hauksson, Egill and Armbruster, John and Dobbs, Steven (1984) Seismicity patterns (1963-1983) as stress indicators in the Shumagin seismic gap, Alaska. Bulletin of the Seismological Society of America, 74 (6). pp. 2541-2558. ISSN 0037-1106.

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Earthquakes (1963 to 1983) of magnitude 5.0 to 6.5 form a rim of high seismic activity around a central region of relative seismic quiescence that coincides with the Shumagin seismic gap. This pattern, which can be inferred both from local network and teleseismic earthquake locations, shows high activity near the eastern and western ends of the seismic gap and along the down-dip end of the main thrust zone. The rim of seismicity surrounding an area of seismic quiescence may reflect strong couplign along the elastic-brittle part of the plate boundary where the great earthquakes occur. The temporal behavior of the microseismicity recorded by the Shumagin network is characterized by a burst of activity in 1978 and 1979, and a low or average level of activity from 1980 to January 1983. The increased microearthquake activity during 1978-1979 is located mainly near the down-dip end of the main thrust zone and along the Benioff zone down to 100 to 200 km depth. Composite fault plane solutions of earthquakes occurring in 1978-1979 show down-dip tension between 50 to 120 km depth in the upper plane of the Benioff zone. Composite fault plane solutions of 1981 earthquakes, however, indicate in-plate compression in the same region. Hence, the rate of occurrence and focal mechanisms of microearthquakes located in the Benioff zone below the main thrust both show coincident temporal and spatial variations that may reflect fluctuations in local stresses.

Item Type:Article
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Hauksson, Egill0000-0002-6834-5051
Additional Information:© 1984 Seismological Society of America. Manuscript received 4 January 1984. Critical reviews were provided by L. Jones, K. Jacob and L. Sykes. Special thanks are due to R. Bilham, D. Simpson and K. Jacob who provided helpful comments and encouragement during the course of this research. I would also like to thank R. Habermann who made his programs available for a critical review of the manuscript and W. McCann for a quick lesson in how to apply the z test. This work was supported by the U.S. Department of Energy (Contracts DE-AC02-76-ER0-3134 and DE-FG-02-84-ER-13221) and the U.S. Geological Survey under the National Earthquake Hazards Reduction Program (Contract USGS 14-08-0001-21299). One of us (S.D.) was supported by the L-DGO (1983) summer internship program. S. Rosen and M. A. Luckman helped with data reduction, and D. Johnson and L. Skinta provided technical assistance for the Shumagin network. L. Niebour typed the manuscript and K. Nagao and M. A. Luckman drafted the figures.
Group:Seismological Laboratory, Division of Geological and Planetary Sciences
Funding AgencyGrant Number
Department of Energy (DOE)DE-AC02-76-ER0-3134
Department of Energy (DOE)DE-FG-02-84-ER-13221
Lamont-Doherty Geological ObservatoryUNSPECIFIED
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Columbia University Lamont-Doherty Geological Observatory3716
Issue or Number:6
Record Number:CaltechAUTHORS:20130419-131545364
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Official Citation:Egill Hauksson, John Armbruster, and Steven Dobbs Seismicity patterns (1963-1983) as stress indicators in the Shumagin seismic gap, Alaska Bulletin of the Seismological Society of America, December 1984, v. 74, p. 2541-2558
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:38041
Deposited By: Ruth Sustaita
Deposited On:23 Apr 2013 16:02
Last Modified:03 Oct 2019 04:53

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