2008 National Seismic Hazard Maps - Source Parameters

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Fault Name	State
Mission fault	Montana

GEOMETRY
Dip (degrees)	60/50/40
Dip direction	W
Sense of slip	normal
Rupture top (km)	0
Rupture bottom (km)	15
Rake (degrees)	-90
Length (km)	92

MODEL VALUES
Probability of activity	1
Minimum magnitude	6.5
Maximum magnitude	7.36
b-value	0.8

Assigned Dip	Fault-Parallel Slip Rate	Width	Annual Rate	a-value	Branch Weight
40	0.50	23.3	2.62e-04	1.670	0.2
50	0.42	19.6	1.84e-04	1.518	0.6
60	0.37	17.3	1.44e-04	1.411	0.2

Comments

The assigned slip rate is based on data from the North Crow and Marsh Creek sites of Ostenaa and others (1990). They document 6-7 m of offset at the North Crow site in the past 15-19 k.y. and 4 m of offset at the Marsh Creek site in the same time interval. The slip rate is the average of the four possible maximum and minimum rates. Dip of fault changed to 50? based on redefined regional default value (Lund, 2006).

Selected References

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. Ostenaa, D.A., Levish, D.R., and Klinger, R.E., 1995, Mission fault study: U.S. Bureau of Reclamation Seismotectonic Report 94-8, 111 p.