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Earthquake Summary

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.

Earthquake Information for MONTANA

Earthquake Details

Magnitude	5.6
Date-Time	Tuesday, July 26, 2005 at 04:08:35 (UTC) = Coordinated Universal Time Monday, July 25, 2005 at 10:08:35 PM = local time at epicenter Time of Earthquake in other Time Zones
Location	45.411°N, 112.596°W
Depth	5 km (3.1 miles) set by location program
Region	WESTERN 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 Uncertainty	horizontal +/- 2.8 km (1.7 miles); depth fixed by location program
Parameters	Nst=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 ID	usazad

Earthquake Maps

Earthquake Location

Location Maps

Historical Seismicity

Seismic Hazard Map

EQ Density Map

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Scientific & Technical Info

• NEIC Moment Tensor Solution
• Harvard Moment Tensor Solution
• Historical Moment Tensor Solutions
• Phase Data
• Theoretical P-Wave Travel Times

Additional Information, News Reports

• 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.

  
  
• News Release
• Earthquake Summary Poster
• ShakeMap shaking intensity maps (Global server)