Magnitude 5.6 - WESTERN MONTANA
2005 July 26 04:08:35 UTC
- This event has been reviewed by a seismologist.
|Depth||5 km (3.1 miles) set by location program|
20 km (15 miles) N of Dillon, Montana
65 km (40 miles) S of Butte, Montana
70 km (45 miles) ESE of Wisdom, Montana
140 km (85 miles) SSW of HELENA, Montana
|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
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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.
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.
Scientific & Technical Information
- Preliminary Earthquake Report
- U.S. Geological Survey, National Earthquake Information Center:
World Data Center for Seismology, Denver