Regional Location:

Preliminary Magnitude:

Greenwich Mean Date:
Greenwich Mean Time:
Focal Depth:


5.3 (NEIC / UUSS)

5.0 km - Fixed

Seismo-Watch Significant Earthquake Reports- No. 01-011
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IDAHO FALLS, IDAHO, April 21, 2001 (Seismo-Watch) -- Preliminary data indicates that an earthquake measuring M5.3 (NEIC / UUSS) occurred at 17:19 UTC (11:19 a.m. local time), April 21 about 49 miles south-southeast of Idaho Falls and 56 miles east of Pocatello in southeastern Idaho, near the small town of Wayan, shaking a wide area of the Idaho-Wyoming border region but not causing any serious damage.

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The earthquake was centered about 3 miles southwest of Wayan along the eastern flank of the Grays Range. The focal point was fixed at a depth of 5.0 km below the surface and the fault plane solutions from NEIC and Harvard indicated nearly pure normal-slip (extension motion) along a moderate dipping and generally north-south or north-northeast trending plane. This type of fault motion is common for earthquakes along the eastern margin of the Basin and Range.

Preliminary reports indicate the quake was widely felt in the region and as far away Idaho Falls, Pocatello, Montpelier and Malad City. It was also felt at Teton Village, and Star Valley, Wyoming.

Although we do not have reports from the epicentral area, tectonic action at this magnitude and location may have caused items to topple from tables and shelves, knocked pictures from walls, and cracked some walls. We do not expect any structural damage.

Most people in outlying areas describe the shaking as a mild rumbling of the ground lasting for a few seconds.

It was preceded five minutes earlier (17:13:48 - UTC) by a M3.5 foreshock and there have been a few small aftershocks detected but data has not been processed at this time.

It was the largest earthquake in this area since the February 2, 1994 Draney Peak M5.8 earthquake. That quake was centered about 17 miles to the southeast and caused light to moderate damage in Star Valley, Wyoming. It was followed by a robust aftershock sequence, which lasted for several months and included dozens of M3s and M4s and a few in the M5 range.

Micro- and macroseismic activity is relatively common in southeastern Idaho, consisting mostly of a couple M1s and M2s per week with an occasional moderate jolt. In 1992, a series of light to moderate earthquakes struck the Grays Lake area located slightly north of the 2001 earthquake series. Suzette Jackson of INEL, Idaho National Engineering and Environmental Laboratory, summerizes the Grays Lake series here.

The geology of the region is fascinating and earthquakes have played an important role in its development. See the links below for more information:

Additional Seismic information links:

Seismograms of the Wayan earthquake from nearby stations:
News Reports:
There have been no national wire news reports at this time
Report update: 8:00 a.m., Monday, April 23, 2001
Click on the image to see a detailed map.
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