Historic Earthquakes

Eastern Idaho
1975 03 28 02:31 UTC (local 03/27)
Magnitude 6.2
Intensity VIII

In the Ridgedale area of the sparsely populated Pocatello Valley, this earthquake shifted several ranch houses on their foundations and toppled many chimneys. At Malad City, 20 kilometers northeast of the epicenter, about 40 percent of the chimneys on old buildings were damaged. Total property damage was estimated at $1 million.

Geologists observed one zone of ground fractures - about 0.6 kilometers long and 5 centimeters wide - in the south-central section of the valley. The shock triggered many snow avalanches northeast of the valley. Fourteen aftershocks ranging in magnitude from 3.8 to 4.7 were located through March 31. Felt in parts of Colorado, Idaho, Nevada, Utah, and Wyoming.

Abridged from Seismicity of the United States, 1568-1989 (Revised), by Carl W. Stover and Jerry L. Coffman, U.S. Geological Survey Professional Paper 1527, United States Government Printing Office, Washington: 1993.

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