New Mexico Geological Society Annual Spring Meeting — Abstracts

We have developed a method of geologic mapping with a total station that enables recognition of faults that have as little as 15 cm of vertical displacement, even in highly vegetated areas. Total station mapping produces 3-D digital data, which are easily integrated into GIS and 2-D and 3-D modeling software for data analysis and visualization. Employing our method in the Pajarito fault system has allowed us to develop a detailed spatial understanding of deformation, most of which would have been overlooked by conventional mapping techniques. The Pajarito fault system comprises the main down-to-the-east, rift-bounding Pajarito fault (PF), and the antithetic Rendija Canyon and Guaje Mountain faults (RCF and GMF, respectively), all of which have paleoseismic evidence for Holocene earthquakes. Near the northern end of Los Alamos National Laboratory (LANL), the PF is a north-trending, segmented, east-facing monocline with >30 m of vertical separation, and the RCF and GMF consist of a few main north-trending strands that have well defined escarpments with >30 m of vertical down-to-the-west separation in the Bandelier Tuff. Southwards along strike the PF has a well-defined escarpment with >75 m of vertical separation and the RCF curves towards the PF and splays into a broad, 1.5-km-wide zone of distributed deformation that may be near the termination of the RCF. Individual faults in this portion of the RCF have <3 m of vertical offset, and total offset across the zone is <9 m. At the south end of LANL, vertical separation is >135 m on the PF, and a zone of dominantly downwest deformation associated with the PF extends at least 1.5 km east of the main PF escarpment. These along-strike variations in the Pajarito fault system, revealed through detailed total station geologic mapping, may have implications for interactions among the three main faults.