Seismicity and focal mechanisms of the central Centennial Tectonic Belt, southwestern Montana and east-central Idaho
Conference
·
· Geological Society of America, Abstracts with Programs; (United States)
OSTI ID:5022779
- Montana Tech, Butte, MT (United States). Montana Bureau of Mines and Geology
The parabolic seismic belt flanking the Snake River Plain is a first-order feature of US seismicity maps. The northern limb of this parabola -- the Centennial Tectonic Belt (CTB) -- extends from NW Yellowstone Park westward through east-central Idaho. The 1959 Hebgen Lake (M[sub s]=7.5) and 1983 Borah Peak (M[sub s]=7.3) earthquakes occurred within the CTB. The Montana Bureau of Mines and Geology located 1,989 earthquakes along the CTB between Hebgen Lake and the Lost River Range (111.25[degree]--113.75[degree]W) from 1982 through Jan. 20, 1993. A distinct, S45[degree]W-trending seismic zone originates in the southern Madison Valley, traverses the southern Gravelly Range and Centennial Valley, and ends in the western Centennial Range. Microearthquakes sharply define the southeast edge of this zone; virtually no seismicity occurs in the eastern Centennial Valley southeast of this zone. Fault plane solutions for 47 better-located events indicate predominantly normal to strike-slip faulting. About 70% of the fault plane solutions have north-south T-axes, however, earthquakes in the western centennial Valley are apparently not occurring on the Centennial Fault. Throughout the central CTB, seismicity does not occur along mapped Quaternary faults. In the Red Rock Valley, seismicity clusters near the endpoints of two mapped faults. A magnitude 4.0 earthquake occurred in a prominent seismic gap west of the MT-ID border on August 28, 1992. The epicenter location and fault plane solution suggest this quake occurred on a valley-bounding fault west of the Birch Creek Valley and not on the main Beaverhead Fault.
- OSTI ID:
- 5022779
- Report Number(s):
- CONF-9305259--
- Conference Information:
- Journal Name: Geological Society of America, Abstracts with Programs; (United States) Journal Volume: 25:5
- Country of Publication:
- United States
- Language:
- English
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