THE EFFECTIVENESS OF CAPACITIVELY-COUPLED RESISTIVITY METHODS IN MAPPING THE INTENSITY AND SPATIAL DISTRIBUTION OF KARST GEOHAZARDS ALONG FM 2185 CULBERSON COUNTY, TEXAS

Located in the northernmost region of the Chihuahuan Desert, the Delaware Basin of West Texas and New Mexico is the western subdivision of the larger Permian Basin. Extensive karst phenomena are found throughout the Permian evaporites of the Gypsum Plain. Geohazards such as sinkholes, subsidence features, and caves pose a continuous threat to infrastructure that extends across Castile and Rustler strata. Land reconnaissance surveys conducted along Farm to Market Road 2185 (FM 2185) during the summer of 2019 identified numerous surficial manifestations of karst features; eight unique regions were designated based on the presence of: 1) geologic strata that support karst development; 2) soil composition and associated suffosion potential; 3) manifestation of karst phenomena expressed at the land surface; and 4) relative potential geohazard risk to infrastructure.

This study encompasses of a 48-kilometer segment of undeveloped FM 2185. Capacitively-Coupled Resistivity (CCR) methods were used to delineate karst features that pose potential geohazard concerns. Data was acquired with the Geometrics OhmMapper G-858 resistivity system, which uses a dipole-dipole TR-5 configuration, composed of five receivers and a transmitter connected by 2.5-meter coaxial cables with a transmitter offset of 2.5 meters. This geometric configuration enabled resistivity reading up to ~2.5 meters deep. Data was processed using MagMap2000 and AGI’s (Advanced Geometrics Inc.) EarthImager 2D software to produce inverted resistivity sections. This enabled the interpretation and characterization of potential subsurface karst related features. The OhmMapper G-858 resistivity meter proved to be an effective tool in the rapid delineation of potential geohazards. The 48-kilometer CCR survey of FM 2185 resulted in the delineation of previously undocumented karst phenomena including potential caves, brecciation, solution-widened fractures and suffosion features. Spatial comparison of inverted resistivity data with high-resolution color infrared imagery and LiDAR-derived elevation models of the study area, displays a positive correlation between the surface phenomena and the resistivity signatures.