AN UPDATED MAP OF QUATERNARY FAULTS AND FOLDS IN NEW MEXICO

Originally compiled in 1998 by USGS personnel, the map of Quaternary faults and folds in New Mexico was recently improved through studies employing a combination of field mapping, geochronology, and remote sensing techniques. We synthesize recent studies and remap Quaternary structures in order to present an updated version of this map, which will allow better characterization of seismic hazards in New Mexico. Originally digitized at scales of 1:100,000 to 1:250,000, the vast majority (94%) of these structures have been refined to 1:24,000 scale using available geologic mapping of 7.5-minute quadrangles and photogrammetric analyses. Specifically, we used stereogrammetry software (Stereo Analyst for ArcGIS 10.1, an ERDAS extension, version 11.0.6) to accurately place scarp- and lineament-forming structures with planimetric and vertical accuracy of ~5 m. This technique typically resulted in shifts of fault locations tens of meters from original plotted traces; whereas some fault strands shifted nearly 1 km. A subset of faults chosen based on their rupture history and proximity to urban centers will be surveyed in the field using a differential GPS (DGPS) system in order to further test the accuracy of stereogrammetric and field mapping. Results of the current effort show that the state features 153 structures with known Quaternary deformation, of which 19 faults exhibit evidence for Holocene rupture. In addition, analyses indicate that some previously mapped faults are actually non-tectonic geomorphic features, underscoring the need for coupled stereogrammetry/remote sensing and field-based investigations of suspected Quaternary structures. New fault length calculations and age and recurrence interval estimates for many faults have implications for rupture models and seismic hazard analyses, particularly in the urban corridor of New Mexico’s Middle Rio Grande Valley. This newly revised dataset thus catalogues numerous structures of interest to both geoscientists and the public at a scale appropriate for an array of future investigations. Geographic information system (GIS) files and associated fault descriptions for this dataset are available to the public online at http://earthquake.usgs.gov/hazards/qfaults/.