PERMFILE50024

• Permit No: M1988112
• IBM Index Class Name: Permit File
• Doc Date: 11/8/1988
• Section_Exhibit Name: APPENDIX B SEISMOLOGY STUDY
• Media Type: D
• Archive: No

i 1
' In a comprehensive study of the La Jencia fault zone
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(1986) d
Socorro,
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ac
ette
ocuments as
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many as six segments on the 35 km long fault with a recurrence
' interval between 6,000 and 3,000 years. Machette's analysis
illuminates numerous parallels between the La Jencia Eault
zone and the Sangre de Cristo fault zone, including the apparent
reactivation o£ a relatively sluggish tectonic mountain front
' in the Holocene.
Figures 2 and 3 present a compilation of the foregoing
information to show trends within the Rio Grande Rift.
Although the data are sparse some trends do appear. For
example, the deformation rate (Figure 3, open circlesi over
' the entire rift appears relatively constant along the length
of the Rio Grande Rift. As the rift widens to the south,
however, deformation is distributed over more faults, decreasing
the deformation rate on individual fault segments (Figure 3,
' closed circles). As the rift widens and the ratio of c^xtension
to uplift increases to the south, the return period decreases
t (Figure 2, bars), fault segmentation increases (length of
single event scarps decrease, Figure 2, triangles) an<I the
~ maximum Likely earthquake magnitude per event decreas<zs (Figure
' 3, crosses). Figure 2 also indicates that a fault segmentation
for the Sangre de Cristo fault of 25 km appears compatible
' with single event fault segmentation results south of the study
are a, as suggested by McCalpin's data, presented in Figure 1
' above.
In way of summary, the published data support thc~ following
' fault rupture potential for San Luis Valley:
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e .. roug
ata presente
n
a
y
a
Rupture Recurrence -
suggest a 25% chance that the fault rupture recurrence
' is less than 10,000 years, a 50% chance that i_t is Less
than 20,000 years, a 75% chance that it is less than
' 40,000 years and a 99+% chance that the fault rupture
recurrence is less than 100,000 years. It has been
' 1,940 to 4,715 years since the Last fault rupture on
the San Luis fault segment adjacent to the site.

' 9