HR: 0830h
AN: S11D-0327    [PDF]
TI: Late Quaternary Surface Rupture and Associated Transpressive Uplift on a Section of the State Line Fault in the south-central Amargosa Desert Basin, Southwestern Nevada
AU: * Menges, C M
EM: cmmenges@usgs.gov
AF: USGS, 520 N. Park Ave, Tucson, AZ 85719 United States
AU: Fridrich, C
AF: USGS, Denver Federal Center, Denver, CO 80225 United States
AU: Blakely, R J
AF: USGS, 345 Middlefield Rd, Menlo Park, CA 94025 United States
AU: Thompson, R A
AF: USGS, Denver Federal Center, Denver, CO 80225 United States
AB: New geomorphic, geophysical, and structural data indicate that a section of the Pahrump-Stewart Valley (State Line) fault on the northern piedmont of the Resting Spring Range is associated with late Quaternary surface rupture and related transpressive domal uplift. Detailed aeromagnetic and gravity data clearly image this northwest-trending strike-slip fault in the subsurface as a continuous multi-strand fault system that continues $>$35 km further northwest into the south-central Amargosa Desert basin than previously established. This continuation of the fault consists of a sigmoidal bend characterized by a constraining bend on the north flank of the Resting Spring Range, paired with a releasing bend on the north flank of the southeastern Funeral Mountains. Bedrock mapping in the Amargosa Desert indicates a cumulative late Cenozoic right-lateral displacement of $\sim$15 km across the entire fault zone. In the Resting Spring area, the major central strand of the State Line fault zone is inactive but offsets playa facies of the Artists Drive Formation (equivalent), internally folded into a giant southeast-plunging chevron syncline, against fluvial and playa margin facies of the same formation that are folded into a broad northwest-plunging anticline. These deformed Tertiary strata are exposed in the core of a large (10 x 18 km) domal Quaternary uplift, centered on the northern piedmont of the range, that coincides with a major transpressive left-step in the adjoining active trace of the fault zone. The domal uplift is indicated by persistent incision into Tertiary bedrock (1-5$^{+}$ m deep) beneath stepped sequences of straths capped by thin and locally warped mid-Pleistocene to Holocene alluvial-gravel veneers. Quaternary activity on the fault zone in this area is now focused on a strand along the northern and eastern border of the uplifted area marked by a discontinuous, 8-10 km long series of aligned, en-echelon, or anastomosing fault scarps that commonly bound linear pressure ridges cored by internally deformed Tertiary strata. These scarps dip steeply up to $20\deg$-$30\deg$ downslope at the base of the uplifted ridges, vary in height from 0.2-2.7 m, and are associated with persistent right-lateral gully offsets of 0.5-5.2 m. The geomorphic data indicate varying amounts of lateral and vertical (reverse) surface displacements, depending on location and orientation within the overall left-stepping fault zone. Combined measurements of vertical and lateral displacement at 10 sites yield estimates of right-oblique net slip for the most recent faulting event that range from 1.9-5.2 m (averaging 3.1 m). A latest Holocene ($<$2ka) age is estimated for this surface rupture based on both stratigraphic relations to surficial deposits and scarp morphology. Geomorphic evidence for prior ruptures is absent or poorly constrained, but generally suggests recurrence intervals at least on the order of 10$^{4}$ yrs. Paleoseismic interpretations of the net-slip displacement data suggest that the fault scarps are probably associated with a {\bf M} 7.1-7.3 paleoearthquake along a rupture zone on the State Line fault that, although not studied in detail, most likely continued $\sim$ 35-40 km to the southeast from the Resting Spring area through Stewart and northwestern Pahrump Valleys. The Holocene surface rupture at the Resting Springs area is unlikely to extend northwest along the northeastern flank of the southeastern Funeral Mountains because upper to middle Pleistocene surfaces are only locally warped, with no detectable fault scarps, in that area.
DE: 1219 Local gravity anomalies and crustal structure
DE: 7221 Paleoseismology
DE: 7223 Seismic hazard assessment and prediction
DE: 8010 Fractures and faults
DE: 8107 Continental neotectonics
SC: Seismology [S]
MN: 2003 Fall Meeting