Reconnaissance evaluation of a potential future sinkhole using integrated simple surface geophysics and surface monitoring points NCKRI Symposium 2: Proceedings of the Thirteenth Multidisciplinary Conference on Sinkholes and the Engineering and Environmental Impacts of Karst

The Arizona Department of Water Resources (ADWR), using satellite-based Interferometric Synthetic Aperture Radar (InSAR) to assess subsidence in parts of Arizona, has identified several subsidence features consistent with potential future sinkholes in an area with several hundred natural evaporite karst depressions or sinkholes. An initial reconnaissance geophysical subsurface evaluation at the most significant of these features was performed in September 2012. Subsurface geo-material strength profiles to depths commonly in excess of 100 meters can be obtained using relatively simple, unobtrusive and inexpensive seismic surface wave (s-wave) geophysical methods such as Refraction Microtremor (ReMi). ReMi can utilize ambient ground vibrations from natural sources or deliberate sources such as vehicle traffic or construction equipment. Shallow ReMi has been applied in conjunction with seismic refraction to characterize shallow subsurface material strength as part of assessing the potential for collapse of an evaporate brine cavern into a large sinkhole in southeast New Mexico, but had not been specifically applied to assessing subsurface conditions in the deeper subsurface above and in the vicinity of a possible impending sinkhole. Two deep ReMi surface wave soundings and two resistivity soundings using the Wenner array method were performed, one each within and outside of the extent of current subsidence as derived from the InSAR. Surface wave velocity profiles indicated relatively low velocity materials extending to depths of 36 to 50 meters; surface wave velocities within the subsidence zone were lower (weaker material) than surface wave velocities outside the zone. The underlying horizon had high surface wave velocities indicating relatively competent rock. Deep resistivity soundings indicated possible lithologic change at depths of roughly 120 to 150 meters. Results of this work, including interpretations and assessments of knowledge gained, practical additional assessment work that could be performed, and some as yet unanswered questions are presented. -- Authors Open Access - Permission by Publisher See Extended description for more information