60-51 Multidisciplinary Approach to Investigating the Neotectonics of the Hachita Valley Fault

Session: 2YC and 4YCU Geoscience Student Research Poster Showcase

Poster Booth No.: 51

Presenting Author:

Gabrielle Eskew

Authors:

Brochstein, Shea¹, Eskew, Gabrielle², Carter, Zachary³, Braddock, Jayla⁴, Murphy, Michael A.⁵, Garcia, Isabela⁶, Allison, Michael⁷, Hoxey, Andrew⁸

Abstract:

The Little Hatchet Mountains, located 4 km east of Playas, New Mexico are a consequence of eastward subduction of the Farallon plate beneath the North American plate followed by its subsequent westward peeling (rolling) back. Its eastern margin is bordered by the Hachita Valley Fault, a product of extensional stresses generated during the rollback stage of the Farallon plate or plate movement along the western margin of North America. The USGS Quaternary Fault and Fold database classifies the fault as “Active”. However, direct estimates of its age and geometry do not exist, making evaluation of its seismic risk and role in geologic models highly unconstrained. The following methods were used: 1) SfM photogrammetry combined with satellite mapping, 2) scarp diffusion analysis using a 1m DEM, 3) GNSS analysis across 47 stations, and regional cross section construction. Our results show that the Hachita valley fault is part of a dominantly east-dipping imbricate system of normal faults, that cut bajadas flanking north striking ranges. A single east-facing scarp with < 2 meters of vertical separation within a sequence of alluvial deposits can be traced for ~ 6km along strike where it is not covered by the youngest alluvial fan deposits. Results from scarp diffusion age modeling indicate the Hachita Valley fault last ruptured at roughly 30 kya. This age is possibly too old due the abundance of a 0.5 m thick caliche layer in the offset alluvial deposit, thereby increasing the cohesion of the ruptured sediment. GPS analysis indicates the fault is slipping at 2.17 mm/yr in a normal-sense. This represents as much as one-tenth of the east-west extensional strain at this latitude in the southern Rocky mountains. GNSS velocities along an east-west traverse through northern New Mexico and southern New Mexico both show stations in the west are moving faster to the west than stations in the east. As the Rio Grande rift crosses the GNSS transects on their eastern sides favors hypotheses that call upon extensional strain to be localized along active rift-bounding normal faults, rather than distributed across southern Basin & Range. Moreover, the absence of earthquakes within the study area, despite the presence of a relatively young fault scarp, indicates that the region currently poses little to no seismic hazard to the region.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9017

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