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Distributed Quaternary Faulting in the Española Basin, Central Rio Grande Rift

Session: Cryptic Faults: Assessing Seismic Hazard on Slow Slipping, Blind or Distributed Fault Systems [Poster]

Type: Poster

Date: 4/21/2021

Presentation Time: 11:30 AM Pacific

Description: 

The Española Basin in the central Rio Grande Rift of northern New Mexico is a slowly deforming, 60-km-wide region, with low rates of extension constrained geodetically (~1 mm/yr) and low slip rate Quaternary-active faults. Prior work suggests late Quaternary deformation is concentrated on faults bounding the western basin margin, with a segmented primary fault system comprising the Pajarito, Santa Clara, and Embudo faults. Faults within and on the eastern margin of the Española Basin are described as antithetic or secondary faults and have previously been considered inactive during the late Quaternary. Faults outside and west of the Española Basin are also considered inactive, as strain focused on the primary fault system in the Miocene-Pliocene. For seismic hazard assessment, we seek to understand if the secondary or antithetic faults accommodate Quaternary deformation, to assess the recency, style, and rate of faulting, and to characterize strain distribution in the basin. Analysis of lidar, optical imagery, and field observations, combined with previous mapping, yields evidence for low-rate Quaternary activity on four faults away from the primary fault system in the Española Basin. The Picuris-Pecos and Nambe-Santa Fe faults are located on the eastern margin while the La Cañada del Amagre and Cañones faults are located farther west of the primary fault system. These faults have distributed, short (<15 km), N-S to NNE-SSW strands that vertically offset Pleistocene and possibly Holocene terraces and glacial deposits by <4 m, with limited evidence for oblique motion. The presence of low-rate active faults away from the primary fault system suggests that strain is distributed on several faults across the basin. However, the small vertical offsets and subtle evidence of deformation on the Picuris-Pecos, Nambe-Santa Fe, La Cañada del Amagre, and Cañones faults indicates that the primary fault system has likely accommodated most of the strain during the late Quaternary.

Presenting Author: Jessica A. Thompson Jobe

Student Presenter: No

Authors