2008 National Seismic Hazard Maps

2008 National Seismic Hazard Maps-Fault parameters

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Fault Name	State
West Valley fault	Utah

GEOMETRY
Dip (degrees)	40/50/60
Dip direction	E
Sense of slip	normal
Rupture top (km)	0
Rupture bottom (km)
Rake (degrees)	-90
Length (km)	16

MODEL VALUES
Probability of activity	0.25
Minimum magnitude	6.5
Maximum magnitude	6.50
b-value	0.8

Assigned Dip	Fault-Parallel Slip Rate	Annual Rate	a-value	Branch Weight
40	0.62	4.54e-04	n/a	0.5
50	0.52	3.86e-04	n/a	0.2
60	0.46	3.58e-04	n/a	0.5

Comments
Preferred vertical slip rate is consensus value reported by Lund (2004) based on original investigations by Keaton and others (1987) and Keaton and Curry (1989). Dip of fault changed to 50? based on redefined regional default value (Lund, 2006). Location of the surface trace of the fault replaced by representation of the Taylorsville scarp in March 2009 instead of Granger scarp as in prior iterations of the maps. West Valley fault is believed to be truncated at depth by the Wasatch fault. West Valley fault is modeled as 25% independent rupture. Bottom of the West Valley fault varies between 5 and 10 km depending on the combination of modeled dips for the Wasatch and West Valley faults.

Comments

Preferred vertical slip rate is consensus value reported by Lund (2004) based on original investigations by Keaton and others (1987) and Keaton and Curry (1989). Dip of fault changed to 50? based on redefined regional default value (Lund, 2006). Location of the surface trace of the fault replaced by representation of the Taylorsville scarp in March 2009 instead of Granger scarp as in prior iterations of the maps. West Valley fault is believed to be truncated at depth by the Wasatch fault. West Valley fault is modeled as 25% independent rupture. Bottom of the West Valley fault varies between 5 and 10 km depending on the combination of modeled dips for the Wasatch and West Valley faults.

Selected References
Keaton, J.R., Currey, D.R., and Olig, S.J., 1987, Paleoseismicity and earthquake hazards evaluation of the West Valley fault zone, Salt Lake urban area: Technical report to U.S. Geological Survey, under Contract 14-08-0001-22048, April 1986 (Draft), 18 p. Keaton, J.R., and Currey, D.R., 1989, Earthquake hazard evaluation of the West Valley fault zone in the Salt Lake City urban area, Utah: Technical report to U.S. Geological Survey, Salt Lake City, under Contract 14-08-001-G1397, 69 p. Lund, W.R., 2005, Consensus preferred recurrence interval and vertical slip rate estimates—Review of Utah paleoseismic-trenching data by the Utah Quaternary Fault Parameters Working Group: Utah Geological Survey Bulletin 134, compact disk. 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

Keaton, J.R., Currey, D.R., and Olig, S.J., 1987, Paleoseismicity and earthquake hazards evaluation of the West Valley fault zone, Salt Lake urban area: Technical report to U.S. Geological Survey, under Contract 14-08-0001-22048, April 1986 (Draft), 18 p.
Keaton, J.R., and Currey, D.R., 1989, Earthquake hazard evaluation of the West Valley fault zone in the Salt Lake City urban area, Utah: Technical report to U.S. Geological Survey, Salt Lake City, under Contract 14-08-001-G1397, 69 p.
Lund, W.R., 2005, Consensus preferred recurrence interval and vertical slip rate estimates—Review of Utah paleoseismic-trenching data by the Utah Quaternary Fault Parameters Working Group: Utah Geological Survey Bulletin 134, compact disk.
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.