2008 National Seismic Hazard Maps

2008 National Seismic Hazard Maps-Fault parameters

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Fault Name	State
Lemhi fault	Idaho

GEOMETRY
Dip (degrees)	60/50/40
Dip direction	SW
Sense of slip	normal
Rupture top (km)	0
Rupture bottom (km)	15
Rake (degrees)	-90
Length (km)	147

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	0.34	23.3	2.160	0.2
50	0.29	19.6	2.007	0.6
60	0.25	17.3	1.901	0.2

Comments
The preferred vertical slip rate is based on the average of a variety of data. Trenching by Baltzer (1990) suggests a slip rate of 0.17 mm/yr, and trenching at two sites by Hemphill-Haley and others (1992) indicates a slip rate of 0.27 mm/yr and 0.32 mm/yr, respectively. In addition, measurements of multiple-event scarps by Haller (1988) suggest slip rates of 0.18 mm/yr, 0.28 mm/yr, and 0.086 mm/yr. Assigned characteristic magnitude based on Borah peak earthquake. Dip of fault changed to 50? based on redefined regional default value (Lund, 2006).

Comments

The preferred vertical slip rate is based on the average of a variety of data. Trenching by Baltzer (1990) suggests a slip rate of 0.17 mm/yr, and trenching at two sites by Hemphill-Haley and others (1992) indicates a slip rate of 0.27 mm/yr and 0.32 mm/yr, respectively. In addition, measurements of multiple-event scarps by Haller (1988) suggest slip rates of 0.18 mm/yr, 0.28 mm/yr, and 0.086 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east-central Idaho, and Red Rock fault, southwest Montana, during the late Quaternary: Boulder, University of Colorado, unpublished M.S. thesis, 141 p., 10 pls. Baltzer, E.M., 1990, Quaternary surface displacement and segmentation of the northern Lemhi fault, Idaho: Binghamton, State University of New York, unpublished M.S. thesis, 88 p., 2 pl., scale 1:62,500. Turko, J.M., 1988, Quaternary segmentation history of the Lemhi Fault, Idaho: Binghamton, State University of New York, M.A. thesis, 91 p. Hemphill-Haley, M.A., Knuepfer, P.L.K., Forman, S.L., and Smith, R.P., 1992, Paleoseismic investigations of the southern Lemhi fault, Idaho: Technical report to U.S. Department of Energy, under Contract DE-AC07-761D01570, March 1992, 32 p. 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.
Baltzer, E.M., 1990, Quaternary surface displacement and segmentation of the northern Lemhi fault, Idaho: Binghamton, State University of New York, unpublished M.S. thesis, 88 p., 2 pl., scale 1:62,500.
Turko, J.M., 1988, Quaternary segmentation history of the Lemhi Fault, Idaho: Binghamton, State University of New York, M.A. thesis, 91 p.
Hemphill-Haley, M.A., Knuepfer, P.L.K., Forman, S.L., and Smith, R.P., 1992, Paleoseismic investigations of the southern Lemhi fault, Idaho: Technical report to U.S. Department of Energy, under Contract DE-AC07-761D01570, March 1992, 32 p.
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.