Near-Surface Seismic Refraction Methods to Characterize Areas of Karst Geology near Carlsbad, NM

Near-surface seismic refraction methods applied to karst geology can give some ideas as to the nature of the void spaces as well as the stratigraphy of the area. A seismic geophone array was laid out near Carlsbad, NM, an area known to contain karst features. Using an impact (sledge hammer), seismic data was collected along two intersecting lines of geophones as well as two gridded areas to get three-dimensional information. The data was picked for the first arrivals of the P-wave, which were graphed and examined for changes in slope and inconsistencies in shape. The data analyzed shows a two-layer model and some inconsistencies such as polarity reversals and delayed arrival times that may represent karst features. Additional processing is used to enhances these features and map them in three-dimensions. The mapped features are compared with known karst features in the area (e.g. sinkholes) for ground-truth information. These methods may be used in the future for detection and classification of other near-surface voids. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.