2008 National Seismic Hazard Maps

2008 National Seismic Hazard Maps-Fault parameters

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Fault Name	State
Thompson Valley fault	Montana

GEOMETRY
Dip (degrees)	60/40/50
Dip direction	W
Sense of slip	normal
Rupture top (km)	0
Rupture bottom (km)	15
Rake (degrees)	-90
Length (km)	10

MODEL VALUES
Probability of activity	1
Minimum magnitude	n/a
Maximum magnitude	6.22
b-value	n/a

Assigned Dip	Fault-Parallel Slip Rate	Width	Annual Rate	a-value	Branch Weight
40	0.12	23.3	3.48e-04	n/a	0.2
50	0.10	19.6	2.45e-04	n/a	0.6
60	0.09	17.3	1.92e-04	n/a	0.2

Comments
The assigned slip rate is based on data presented by Ostenaa and others (1990). They report that early to mid-Wisconsinian surfaces are offset 6.4 m. The assumed age of the surface is 60-130 ka, and the assigned rate is the average of the maximum and minimum rates calculated from these data. Dip of fault changed to 50? based on redefined regional default value (Lund, 2006).

Selected References
Ostenaa, D., Manley, W., Gilbert, J., LaForge, R., Wood, C., and Weisenberg, C.W., 1990, Flathead Reservation regional seismotectonic study—An evaluation for dam safety: U.S. Bureau of Reclamation Seismotectonic Report 90-8, 161 p., 7 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

Ostenaa, D., Manley, W., Gilbert, J., LaForge, R., Wood, C., and Weisenberg, C.W., 1990, Flathead Reservation regional seismotectonic study—An evaluation for dam safety: U.S. Bureau of Reclamation Seismotectonic Report 90-8, 161 p., 7 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.