2008 National Seismic Hazard Maps

2008 National Seismic Hazard Maps-Fault parameters

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Fault Name	State
Lobato Mesa fault zone	New Mexico

GEOMETRY
Dip (degrees)	50/40/60
Dip direction	W
Sense of slip	normal
Rupture top (km)	0
Rupture bottom (km)	15
Rake (degrees)	-90
Length (km)	19

MODEL VALUES
Probability of activity	1
Minimum magnitude	6.5
Maximum magnitude	6.56
b-value	0.8

Assigned Dip	Fault-Parallel Slip Rate	Width	Annual Rate	a-value	Branch Weight
40	0.01	23.3	1.43e-05	0.424	0.2
50	0.01	19.6	1.00e-05	0.271	0.6
60	0.01	17.3	7.86e-06	0.165	0.2

Comments
Wong and others (1995, 1996) cited a slip rate of 0.05 mm/yr, calculated from 490-520 m of offset of a 10.6 Ma basalt dike. Accordingly, the Lobato Mesa fault was assigned a vertical slip rate of 0.05 mm/yr in the 1996 and 2002 national seismic-hazard maps. However, the source cited by Wong and others had applied the name Lobato Mesa fault zone both to the Lobato Mesa fault and to the parallel, La Canada del Amagre fault 1-2 km farther east. Geologic maps show that the dike1s offset is on the La Canada del Amagre fault (Aldrich and Dethier, 1990; Dethier and Martin, 1984). The dike terminates against the Lobato Mesa fault from the east but is not mapped west of the fault. Similarly, Wong and others cited a 15 m vertical offset of the 1.2 Ma Bandelier Tuff and attributed it to the Lobato Mesa fault, whereas probably this offset, too, is on the La Canada del Amagre fault. A post-mid-Miocene slip rate can be calculated from data that are specific to the Lobato Mesa fault. Dethier and Martin (1984) reported a presumably vertical offset by the Lobato Mesa fault of the Ojo Caliente Sandstone of 70 m or more. The Ojo Caliente Sandstone is 14-12 Ma (Aldrich and Dethier, 1990). Thus, a long-term slip rate for the Lobato Mesa fault can be calculated from 70 m of vertical offset of the sandstone. The middle of the age range gives a vertical slip rate of 0.0054 mm/yr. Absent any other fault-specific slip data, this rate was used in the 2007 and subsequent national seismic-hazard maps. Dip of fault changed to 50? based on redefined regional default value (Lund, 2006).

Comments

Wong and others (1995, 1996) cited a slip rate of 0.05 mm/yr, calculated from 490-520 m of offset of a 10.6 Ma basalt dike. Accordingly, the Lobato Mesa fault was assigned a vertical slip rate of 0.05 mm/yr in the 1996 and 2002 national seismic-hazard maps. However, the source cited by Wong and others had applied the name Lobato Mesa fault zone both to the Lobato Mesa fault and to the parallel, La Canada del Amagre fault 1-2 km farther east. Geologic maps show that the dike1s offset is on the La Canada del Amagre fault (Aldrich and Dethier, 1990; Dethier and Martin, 1984). The dike terminates against the Lobato Mesa fault from the east but is not mapped west of the fault. Similarly, Wong and others cited a 15 m vertical offset of the 1.2 Ma Bandelier Tuff and attributed it to the Lobato Mesa fault, whereas probably this offset, too, is on the La Canada del Amagre fault. A post-mid-Miocene slip rate can be calculated from data that are specific to the Lobato Mesa fault. Dethier and Martin (1984) reported a presumably vertical offset by the Lobato Mesa fault of the Ojo Caliente Sandstone of 70 m or more. The Ojo Caliente Sandstone is 14-12 Ma (Aldrich and Dethier, 1990). Thus, a long-term slip rate for the Lobato Mesa fault can be calculated from 70 m of vertical offset of the sandstone. The middle of the age range gives a vertical slip rate of 0.0054 mm/yr. Absent any other fault-specific slip data, this rate was used in the 2007 and subsequent national seismic-hazard maps. Dip of fault changed to 50? based on redefined regional default value (Lund, 2006).

Selected References
Aldrich, M.J., Jr., and Dethier, D.P., 1990, Stratigraphic and tectonic evolution of the northern Española basin, Rio Grande rift, New Mexico: Geological Society of America Bulletin, v. 102, p. 1695-1705. Dethier, D.P., and Martin, B.A., 1984, Geology and structure along the northeast Jemez Mountains, New Mexico, in Baldridge, W.S., Dickerson, P.W., Riecker, R.E., and Zidek, J., eds., Rio Grande rift—Northern New Mexico: New Mexico Geological Society, 35th Field Conference, October 11-13, 1984, Guidebook, p. 145-150. Wong, I., Kelson, K., Olig, S., Kolbe, T., Hemphill-Haley, M., Bott, J., Green, R., Kanakari, H., Sawyer, J., Silva, W., Stark, C., Haraden, C., Fenton, C., Unruh, J., Gardner, J., Reneau, S., and House, L., 1995, Seismic hazards evaluation of the Los Alamos National Laboratory: Technical report to Los Alamos National Laboratory, Los Alamos, New Mexico, February 24, 1995, 3 volumes, 12 pls., 16 appen. Wong, I., Kelson, K., Olig, S., Bott, J., Green, R., Kolbe, T., Hemphill-Haley, M., Gardner, J., Reneau, S., and Silva, W., 1996, Earthquake potential and ground shaking hazard at the Los Alamos National Laboratory, New Mexico, in Goff, F., Kues, B.S., Rogers, M.A., McFadden, L.D., and Gardner, J.N., eds., The Jemez Mountains region: New Mexico Geological Society, 47th Field Conference, September 25-28, 1996, Guidebook, p. 135–142. 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

Aldrich, M.J., Jr., and Dethier, D.P., 1990, Stratigraphic and tectonic evolution of the northern Española basin, Rio Grande rift, New Mexico: Geological Society of America Bulletin, v. 102, p. 1695-1705.
Dethier, D.P., and Martin, B.A., 1984, Geology and structure along the northeast Jemez Mountains, New Mexico, in Baldridge, W.S., Dickerson, P.W., Riecker, R.E., and Zidek, J., eds., Rio Grande rift—Northern New Mexico: New Mexico Geological Society, 35th Field Conference, October 11-13, 1984, Guidebook, p. 145-150.
Wong, I., Kelson, K., Olig, S., Kolbe, T., Hemphill-Haley, M., Bott, J., Green, R., Kanakari, H., Sawyer, J., Silva, W., Stark, C., Haraden, C., Fenton, C., Unruh, J., Gardner, J., Reneau, S., and House, L., 1995, Seismic hazards evaluation of the Los Alamos National Laboratory: Technical report to Los Alamos National Laboratory, Los Alamos, New Mexico, February 24, 1995, 3 volumes, 12 pls., 16 appen.
Wong, I., Kelson, K., Olig, S., Bott, J., Green, R., Kolbe, T., Hemphill-Haley, M., Gardner, J., Reneau, S., and Silva, W., 1996, Earthquake potential and ground shaking hazard at the Los Alamos National Laboratory, New Mexico, in Goff, F., Kues, B.S., Rogers, M.A., McFadden, L.D., and Gardner, J.N., eds., The Jemez Mountains region: New Mexico Geological Society, 47th Field Conference, September 25-28, 1996, Guidebook, p. 135–142.
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.