Late Cenozoic tectonism of the northern basin-range province, western Montana

Conference · Tue Jan 01 04:00:00 EST 1985 · Geol. Soc. Am., Abstr. Programs; (United States)

OSTI ID:6273774

Stickney, M C; Bartholomew, M J

High-angle, basin-bounding faults were examined north of the Snake River Plain where many are associated with the Intermountain Seismic Belt (ISB). Based on physical characteristics the authors have distinguished four classes of faults: 1) active with recent surface rupture; 2) dormant but likely to be reactivated; 3) inactive faults that might be reactivated; and 4) dead faults that are not likely to be reactivated within the present tectonic framework. All recently active and dormant faults (Quaternary movement) are located within or south of the Lewis and Clark Zone (LCZ), which also marks a change in the character of the seismicity. North of the LCZ no historic earthquakes have exceeded magnitude (M) 5.0. South of the LCZ earthquakes of M 5.0 or greater have occurred. Inactive and dead faults are associated with many intermontane basins north of the LCZ as well as south of the zone but west of the ISB. The ISB south of the LCZ is characterized by a high level of seismicity exemplified by a recurrence time of 10 years for M 6.0 or greater and by the occurrence of about 60 earthquakes of M 2.5 or greater per year. Most active faults (about 15) south of the LCZ trend N30/sup 0/W to N50/sup 0/W, particularly in the seismically active area in SW Montana and adjacent Idaho where the 1973 Borah Peak earthquake (M 7.3) occurred. Only a few active faults trend N-S, NE or E-W. The zone of coincident seismicity and active faults lies along the eastern perimeter of the northern Basin and Range Province. This suggests that Quaternary extension is limited to a relatively narrow frontal belt of the province.

• Research Organization: Montana Bureau of Mines and Geology, Butte (USA)
• OSTI ID: 6273774
• Report Number(s): CONF-8510489-
• Conference Information: Journal Name: Geol. Soc. Am., Abstr. Programs; (United States) Journal Volume: 36
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580201* -- Geophysics-- Seismology & Tectonics-- (1980-1989)
CENOZOIC ERA
CLASSIFICATION
FEDERAL REGION VIII
GEOLOGIC AGES
GEOLOGIC FAULTS
GEOLOGIC FRACTURES
GEOLOGIC STRUCTURES
MONTANA
NORTH AMERICA
QUATERNARY PERIOD
RISK ASSESSMENT
SEISMICITY
TECTONICS
USA