2008 National Seismic Hazard Maps

2008 National Seismic Hazard Maps-Fault parameters

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Fault Name	State
Northern Sangre de Cristo fault	Colorado

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)	185

MODEL VALUES
Probability of activity	1
Minimum magnitude	6.5
Maximum magnitude	7.50
b-value	0.8

Assigned Dip	Fault-Parallel Slip Rate	Width	a-value	Branch Weight
40	0.28	23.3	1.662	0.2
50	0.24	19.6	1.510	0.6
60	0.21	17.3	1.403	0.2

Comments
The preferred vertical vertical slip rate of 0.18 mm/yr s from the Uracca Creek site on the Zapata section, the north-central section of four sections that make up the fault. Scarps are 20.1 and 22.3 m high on a Bull Lake-equivalent (60-180 ka) surface (Kirkham and Rogers, 1981). The mean height divided by the mean age yields 0.18 mm/yr as used in the hazard maps. The characteristic magnitude for this fault is fixed at M7.5 even though the length of the fault would permit a larger earthquake. Dip of fault changed to 50? based on redefined regional default value (Lund, 2006).

Comments

The preferred vertical vertical slip rate of 0.18 mm/yr s from the Uracca Creek site on the Zapata section, the north-central section of four sections that make up the fault. Scarps are 20.1 and 22.3 m high on a Bull Lake-equivalent (60-180 ka) surface (Kirkham and Rogers, 1981). The mean height divided by the mean age yields 0.18 mm/yr as used in the hazard maps. The characteristic magnitude for this fault is fixed at M7.5 even though the length of the fault would permit a larger earthquake. Dip of fault changed to 50? based on redefined regional default value (Lund, 2006).

Selected References
Colman, S.M., McCalpin, J.P., Ostenaa, D.A., and Kirkham, R.M., 1985, Map showing upper Cenozoic rocks and deposits and Quaternary faults, Rio Grande Rift, south-central Colorado: U.S. Geological Survey Miscellaneous Geologic Investigations I-1594, 2 sheets. McCalpin, J., 1981, Quaternary geology and neotectonics of the west flank of the northern Sangre de Cristo Mountains, south-central Colorado: Golden, Colorado School of Mines, unpublished Ph.D. dissertation, 287 p. Wallace, A.R., 1997, Geologic map of the Fort Garland quadrangle, Costilla County, Colorado: U.S. Geological Survey Miscellaneous Field Studies Map MF-2312-E. 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. Crone, A.J., and Machette, M.N., 2005, Paleoseismic activity on the Sangre de Cristo fault near San Luis, Colorado: Geological Society of America Abstracts with Programs, v. 37, no. 7, p. 558. McCalpin, J.P., 1982, Quaternary geology and neotectonics of the west flank of the northern Sangre de Cristo Mountains, south-central Colorado: Colorado School of Mines Quarterly, v. 77, no. 3, p. 1-97. Kirkham, R.M., and Rogers, W.P., 1981, Earthquake potential in Colorado: Colorado Geological Survey Bulletin 43, 171 p., 3 pls.

Selected References

Colman, S.M., McCalpin, J.P., Ostenaa, D.A., and Kirkham, R.M., 1985, Map showing upper Cenozoic rocks and deposits and Quaternary faults, Rio Grande Rift, south-central Colorado: U.S. Geological Survey Miscellaneous Geologic Investigations I-1594, 2 sheets.
McCalpin, J., 1981, Quaternary geology and neotectonics of the west flank of the northern Sangre de Cristo Mountains, south-central Colorado: Golden, Colorado School of Mines, unpublished Ph.D. dissertation, 287 p.
Wallace, A.R., 1997, Geologic map of the Fort Garland quadrangle, Costilla County, Colorado: U.S. Geological Survey Miscellaneous Field Studies Map MF-2312-E.
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.
Crone, A.J., and Machette, M.N., 2005, Paleoseismic activity on the Sangre de Cristo fault near San Luis, Colorado: Geological Society of America Abstracts with Programs, v. 37, no. 7, p. 558.
McCalpin, J.P., 1982, Quaternary geology and neotectonics of the west flank of the northern Sangre de Cristo Mountains, south-central Colorado: Colorado School of Mines Quarterly, v. 77, no. 3, p. 1-97.
Kirkham, R.M., and Rogers, W.P., 1981, Earthquake potential in Colorado: Colorado Geological Survey Bulletin 43, 171 p., 3 pls.