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U.S. Geological Survey Open-File Report 79–670

Interim Report on the St. Elias, Alaska Earthquake of 28 February 1979

By J.C. Lahr, George Plafker, C.D. Stephens, K.A. Folgleman, and M.E. Blakford

1979

Thumbnail of and link to report PDF (17.4 MB)Introduction

On 28 February 1979 an earthquake with surface wave magnitude (Ms) of 7.7 (W. Person, personal communication, 1979) occurred beneath the Chugach and St. Elias mountains of southern Alaska (fig. 1). This is a region of complex tectonics resulting from northwestward convergence between the Pacific and North American plates. To the east, the northwest-trending Fairweather fault accommodates the movement with dextral slip of about 5.5 cm/yr (Plafker, Hudson, and others, 1978); to the west, the Pacific plate underthrusts Alaska at the Aleutian trench, which trends southwestward (Plafker 1969). The USGS has operated a telemetered seismic network in southern Alaska since 1971 and it was greatly expanded along the eastern Gulf of Alaska in September 1974. The current configuration of stations is shown in Figure 9. Technical details of the network are available in published earthquake catalogs (Lahr, Page, and others, 1974; Fogleman, Stephens, and others, 1978). Preliminary analysis of the data from this network covering the time period September 1, 1978 through March 10, 1979, as well as worldwide data for the main shock will be discussed in this paper.

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Contact Information, Earthquake Science Center, Menlo Park Science Center
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http://earthquake.usgs.gov/

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Suggested citation:

Lahr, J.C., Plafker, G., Stephens, C.D., Folgleman, K.A., and Blakford, M.E., 1979, Interim report on the St. Elias, Alaska earthquake of 28 February 1979: U.S. Geological Survey Open-File Report 79–670, 23 p. (Available at http://pubs.usgs.gov/of/1979/0670/.)



Contents

Introduction

Acknowledgments

Tectonic Setting

Geologic Setting

Earthquake History

Seismicity of the St. Elias Region

January 1 Through February 28, 1979 Seismicity

Main Shock

Aftershocks

Responsible Faults

Discussion

References


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