Magnitude 5.6 - WESTERN MONTANA

2005 July 26 04:08:35 UTC

Earthquake Details

Magnitude5.6
Date-Time
Location45.411°N, 112.596°W
Depth5 km (3.1 miles) set by location program
RegionWESTERN MONTANA
Distances
  • 22 km (14 miles) N (8°) from Dillon, MT
  • 25 km (16 miles) SW (234°) from Twin Bridges, MT
  • 32 km (20 miles) W (261°) from Sheridan, MT
  • 351 km (218 miles) NE (54°) from Boise, ID
  • 521 km (324 miles) N (354°) from Salt Lake City, UT
Location Uncertaintyhorizontal +/- 2.8 km (1.7 miles); depth fixed by location program
ParametersNST=128, Nph=128, Dmin=67.8 km, Rmss=0.73 sec, Gp= 40°,
M-type=teleseismic moment magnitude (Mw), Version=6
Source
  • USGS NEIC (WDCS-D)
Event IDusazad
  • This event has been reviewed by a seismologist.
  • Did you feel it? Report shaking and damage at your location. You can also view a map displaying accumulated data from your report and others.

Earthquake Summary

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Felt Reports

Items knocked off shelves at Dillon and Bozeman. Felt (VI) at Dillon and Twin Bridges; (IV) at Bozeman, Butte, Helena, Missoula and West Yellowstone; (III) at Billings, Great Falls, Kalispell and Livingston. Felt (IV) at Island Park and Salmon; (III) at Coeur d'Alene, McCall, Moscow, Rexburg and Sandpoint, Idaho. Also felt (III) at Pullman and Spokane, Washington and in Yellowstone National Park, Wyoming. The quake was felt as far away as Seattle, Washington and Calgary, Alberta.

Tectonic Summary

Montana is one of the most seismically active States in the U.S. Since 1925, the State has experienced five shocks that reached intensity VIII or greater (Modified Mercalli Scale). During the same interval, hundreds of less severe tremors were felt within the State. Montana's earthquake activity is concentrated mostly in the mountainous western third of the State which lies within a seismic zone that includes western Montana, southeastern Idaho, western Wyoming, and central Utah (see Earthquake History of Montana).

There are a variety of fault types represented in this seismic zone. Some faults clearly show evidence of being the source of many large-magnitude earthquakes in the past, and some faults do not. East-central Idaho and western Montana is characterized by long linear mountain ranges with intervening valleys. Geologically young faults bound most or all of these mountain blocks. Many of which are capable of producing large-magnitude earthquakes similar to the largest earthquakes that have occurred historically in the seismic zone (about magnitude 7.5). Seismologists have not yet determined the causative fault of the recent earthquake.

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