2008 National Seismic Hazard Maps

2008 National Seismic Hazard Maps-Fault parameters

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Fault Name	State
Canyon Ferry fault	Montana

GEOMETRY
Dip (degrees)	60/40/50
Dip direction	SW
Sense of slip	normal
Rupture top (km)	0
Rupture bottom (km)	15
Rake (degrees)	-90
Length (km)	39

MODEL VALUES
Probability of activity	1
Minimum magnitude	6.5
Maximum magnitude	6.92
b-value	0.8

Assigned Dip	Fault-Parallel Slip Rate	Width	Annual Rate	a-value	Branch Weight
40	0.20	23.3	2.03e-04	1.382	0.2
50	0.17	19.6	1.43e-04	1.229	0.6
60	0.15	17.3	1.12e-04	1.123	0.2

Comments
Anderson and others (2003, 2005) provide a number of interevent, short-term and long-term slip rates for this fault based on infrared stimulated luminescence (IRSL) ages and offsets from a single trench site. Of all the slip rates documented in their study, we have selected the average slip rate for the past 68 ka for our preferred vertical slip rate. This value was given preference over their short-term higher slip rates because, despite periods when rates may be as high as 0.5 mm/yr, there is no evidence that the fault has had a single surface-faulting earthquake in about 13 k.y. Dip of fault changed to 50? based on redefined regional default value (Lund, 2006).

Comments

Anderson and others (2003, 2005) provide a number of interevent, short-term and long-term slip rates for this fault based on infrared stimulated luminescence (IRSL) ages and offsets from a single trench site. Of all the slip rates documented in their study, we have selected the average slip rate for the past 68 ka for our preferred vertical slip rate. This value was given preference over their short-term higher slip rates because, despite periods when rates may be as high as 0.5 mm/yr, there is no evidence that the fault has had a single surface-faulting earthquake in about 13 k.y. Dip of fault changed to 50? based on redefined regional default value (Lund, 2006).

Selected References
Anderson, L.W., and LaForge, R., 2003, Seismotectonic study for Canyon Ferry Dam, Missouri River Basin Project, Montana: U.S. Bureau of Reclamation Seismotectonic Report 2003-1, 70 p. Anderson, L.W., Olig, S.S., and Forman, S.L., 2005, Paleoseismic investigation of the Canyon Ferry fault, west-central Montana, in Lund, W.R., ed., Proceedings Volume—Basin and Range Province Seismic Hazards Summit II: Utah Geological Survey Miscellaneous Publication 05-2, 17 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

Anderson, L.W., and LaForge, R., 2003, Seismotectonic study for Canyon Ferry Dam, Missouri River Basin Project, Montana: U.S. Bureau of Reclamation Seismotectonic Report 2003-1, 70 p.
Anderson, L.W., Olig, S.S., and Forman, S.L., 2005, Paleoseismic investigation of the Canyon Ferry fault, west-central Montana, in Lund, W.R., ed., Proceedings Volume—Basin and Range Province Seismic Hazards Summit II: Utah Geological Survey Miscellaneous Publication 05-2, 17 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.