2008 National Seismic Hazard Maps

2008 National Seismic Hazard Maps-Fault parameters

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Fault Name	State
Beaverhead fault	Idaho

GEOMETRY
Dip (degrees)	40/60/50
Dip direction	SW
Sense of slip	normal
Rupture top (km)	0
Rupture bottom (km)	15
Rake (degrees)	-90
Length (km)	134

MODEL VALUES
Probability of activity	1
Minimum magnitude	6.5
Maximum magnitude	7.00
b-value	0.8

Assigned Dip	Fault-Parallel Slip Rate	Width	a-value	Branch Weight
40	0.19	23.3	1.856	0.2
50	0.16	19.6	1.704	0.6
60	0.14	17.3	1.597	0.2

Comments
The preferred vertical slip rate is based on geomorphic studies of multiple-earthquake scarps on early Pinedale-equivalent (25-30 ka) surfaces on two of the central segments of the fault (Haller, 1988) that suggest an average of 0.12 mm/yr. Assigned characteristic magnitude based on Borah Peak earthquake. Dip of fault changed to 50? based on redefined regional default value (Lund, 2006).

Selected References
Haller, K.M., 1988, Segmentation of the Lemhi and Beaverhead faults, east-central Idaho, and Red Rock fault, southwest Montana, during the late Quaternary: Boulder, University of Colorado, unpublished M.S. thesis, 141 p., 10 pls. Lund, W.R., ed., 2006, Basin and Range Province Earthquake Working Group seismic-hazard recommendations to the U.S. Geological Survey National Seismic Hazard Mapping Program: Utah Geological Survey Open-File Report 477, 23 p, ugspub.nr.utah.gov/publications/open_file_reports/OFR-477.pdf.

Selected References

Haller, K.M., 1988, Segmentation of the Lemhi and Beaverhead faults, east-central Idaho, and Red Rock fault, southwest Montana, during the late Quaternary: Boulder, University of Colorado, unpublished M.S. thesis, 141 p., 10 pls.
Lund, W.R., ed., 2006, Basin and Range Province Earthquake Working Group seismic-hazard recommendations to the U.S. Geological Survey National Seismic Hazard Mapping Program: Utah Geological Survey Open-File Report 477, 23 p, ugspub.nr.utah.gov/publications/open_file_reports/OFR-477.pdf.