"Montana Seismicity: Historical Earthquakes and Modern Studies"
Summary:
This presentation will include a brief synopsis of Montana’s most significant earthquakes and their effects. Geologic evidence for prehistoric earthquakes in the state and modern seismicity studies will illustrate Montana’s seismic hazards. The presentation will conclude with a question and answer session.
This seminar is scheduled for 3:00pm - 4:00 pm in the conference room of the State Library, 1515 East Sixth Avenue, Helena.
Background:
Montana has a history of destructive earthquakes. These earthquakes occur along the Intermountain Seismic Belt (ISB), a zone of shallow-focus seismicity that extends from the Flathead Valley to Yellowstone National Park and then southward through Salt Lake City and as far south as southern Nevada. A shorter branch of the ISB extends west from Yellowstone through extreme southwestern Montana and into central Idaho.
There are 70 known active or potentially active faults in Montana; however, very few earthquakes can be attributed to mapped faults. In contrast to California, recent small- to moderate-magnitude earthquakes occur on minor faults at depths that are near—but not on—larger mapped faults. The absence of “background seismicity” along primary ISB faults remains unexplained.
Starting in 1980, the Earthquake Studies Office of the Montana Bureau of Mines and Geology in Butte established a network of seismograph stations in western Montana. It has expanded the area of coverage and improved its data quality through cooperative efforts with various agencies, including the U.S. Geological Survey, the Confederated Salish and Kootenai Tribes, the National Institutes of Safety and Health, and Montana Disaster and Emergency Services.
Currently, the Montana seismograph network includes 35 stations from throughout western Montana. Data from this network and stations in surrounding parts of Idaho, Wyoming, Washington, and Canada are used to locate an average of six local earthquakes per day. Computers play an increasingly important role in the acquisition, analysis, and display of these data. The Earthworm data acquisition and analysis system currently in use posts both “raw” seismic data and automatically located seismic events on the Bureau’s website (http://mbmgquake.mtech.edu/) within three to five minutes of real-time.
In addition to basic seismological research, Montana network data are used to characterize seismic hazards, and provide information to emergency responders and dam safety personnel, and answer inquiries from the public and the press.
