2008 National Seismic Hazard Maps

2008 National Seismic Hazard Maps-Fault parameters

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Fault Name	State
Socorro Canyon fault zone	New Mexico

GEOMETRY
Dip (degrees)	60/50/40
Dip direction	E
Sense of slip	normal
Rupture top (km)	0
Rupture bottom (km)	15
Rake (degrees)	-90
Length (km)	49

MODEL VALUES
Probability of activity	1
Minimum magnitude	6.5
Maximum magnitude	7.04
b-value	0.8

Assigned Dip	Fault-Parallel Slip Rate	Width	Annual Rate	a-value	Branch Weight
40	0.04	23.3	3.55e-05	0.580	0.2
50	0.04	19.6	2.50e-05	0.428	0.6
60	0.03	17.3	1.96e-05	0.321	0.2

Comments
This fault was added in the 2007 maps. Recent trenching, mapping, and dating (Phillips and others, 2003) demonstrated the occurrence of three earthquakes that produced scarps on a terrace of Bull Lake age (122?18 ka). The trench across a 3- to 4-m-high scarp exposed two colluvial wedges, which formed following the oldest (1.7 m offset at 92, +16, -13 ka) and intermediate (1.8 m offset at 28, +18, -23 ka) surface ruptures. A profile across the youngest, single-event scarp showed a scarp height of 0.58 m and diffusion modeling indicated that the scarp formed 1.4-1.6 ka. Phillips and others (2003) calculated a vertical slip rate of 0.04 mm/yr since 100 ka; however, this calculation over estimates slip rate because it included the displacement of oldest earthquake and not the entire 122?18 ka. Instead, we use only offsets associated with closed time intervals for the preferred vertical slip rate. Thus, 2.38 m of released strain accumulated between 1.4-1.6 ka and 108-79 ka, or over 77.4-106.6 k.y. The average of the resultant values (0.031-0.022 mm/yr) is assigned as the preferred vertical give vertical slip rate for the Soccoro Canyon fault.

Comments

This fault was added in the 2007 maps. Recent trenching, mapping, and dating (Phillips and others, 2003) demonstrated the occurrence of three earthquakes that produced scarps on a terrace of Bull Lake age (122?18 ka). The trench across a 3- to 4-m-high scarp exposed two colluvial wedges, which formed following the oldest (1.7 m offset at 92, +16, -13 ka) and intermediate (1.8 m offset at 28, +18, -23 ka) surface ruptures. A profile across the youngest, single-event scarp showed a scarp height of 0.58 m and diffusion modeling indicated that the scarp formed 1.4-1.6 ka. Phillips and others (2003) calculated a vertical slip rate of 0.04 mm/yr since 100 ka; however, this calculation over estimates slip rate because it included the displacement of oldest earthquake and not the entire 122?18 ka. Instead, we use only offsets associated with closed time intervals for the preferred vertical slip rate. Thus, 2.38 m of released strain accumulated between 1.4-1.6 ka and 108-79 ka, or over 77.4-106.6 k.y. The average of the resultant values (0.031-0.022 mm/yr) is assigned as the preferred vertical give vertical slip rate for the Soccoro Canyon fault.

Selected References
Phillips, F.M., Ayarbe, J.P., Harrison, J.B.J., and Elmore, D., 2003, Dating rupture events on alluvial fault scarps using cosmogenic nuclides and scarp morphology: Earth and Planetary Science Letters, v. 215, p. 203–218.