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Middle to Late Pleistocene Faulting on the Puye Fault Zone, Española Basin, New Mexico

Description: 

The Española Basin in the central Rio Grande Rift (RGR) of northern New Mexico is a slowly deforming, 60-km-wide region with low geodetic extension rates (~1 mm/yr) and low-slip-rate (0.01–0.1 mm/yr) Quaternary-active faults. While previous work suggests that deformation is accommodated by the Pajarito fault on the western side of the basin, new evidence from neotectonic mapping on 1-m lidar-derived topography and offset geomorphic surfaces suggests that additional RGR faults may have higher slip rates than previously thought. We focus on the Puye fault, a distributed fault system in the central-western Española Basin. The fault zone has at least four subparallel primary strands that offset the same geomorphic surface with a primarily down-to-the-east sense of motion. The fault trends north-south and mapped scarps extend at least 12 km. The highest scarps record up to 12 m of net vertical separation. We excavated three 1- to 2-m-deep pits atop the faulted surface to collect cosmogenic ¹⁰Be and optically stimulated luminescence (OSL) samples to constrain surface ages, pedogenic character, and calculate a slip rate on the Puye fault system. Based on soil development and correlation with similar regional surfaces, we estimate this surface could be Middle Pleistocene (~130 - 774 ka), pending geochronology results. If the age for the faulted surface is middle-late Quaternary, slip rates may exceed known rates on the Pajarito fault (0.1 mm/yr). In a wash that intersects the primary scarp, we observed ~1 m of down-to-the-east offset of fluvial sand and gravel units in a cutbank exposure. Pending OSL ages from the cutbank will test the hypothesis that this exposure records recent fault activity. The presence of smaller offset amounts on potentially younger inset deposits, if confirmed, would indicate the Puye fault system has accommodated several large earthquakes during the middle to late Pleistocene. The results of this work will be used to characterize the Puye fault and reduce uncertainties in inputs for site-specific probabilistic seismic hazard analyses at nearby dams and regional seismic hazard models.

Session: From Faults to Fjords: Earthquake Evidence in Terrestrial and Subaqueous Environments [Poster Session]

Type: Poster

Date: 5/1/2024

Presentation Time: 08:00 AM (local time)

Presenting Author: Jessica

Student Presenter: No

Invited Presentation: 

Authors