Using InSAR to detect subsidence at brine wells, sinkhole sites, and mines

The July 16, 2008, collapse of a brine well southeast of Artesia, New Mexico, has led to concern about the stability of a brine well facility located within the city limits of Carlsbad, New Mexico. Monitoring and mitigation studies were initiated in 2009, and emergency response procedures are in place should it collapse into a large sinkhole. For historic subsidence data, satellite-based Interferometry by Synthetic Aperture Radar (InSAR) provides a method to quantify land subsidence as differential ground movement over time using archived data extending back to 1992. To evaluate InSAR for monitoring and provide a sampling of historic subsidence, data acquired in July 2005, February 2006, and March 2006 were obtained and processed into a July 2005 to March 2006 interferogram. The resulting scene included three study areas: the Carlsbad brine well, underground potash mining in the Carlsbad Mining District, and the collapsed brine well sinkhole southeast of Artesia and north of Carlsbad (Jim's Water Service). Changes in surface elevation were estimated from the unwrapped InSAR results. Random elevation fluctuations in apparently stable areas were considered to be 'noise'. After simple smoothing by averaging three adjacent data points, resulting standard deviations were less than 2 mm. No differential subsidence above 'noise' was interpreted across either of the brine wells from July 2005 to March 2006. Precursor subsidence was not indicated 2 years before the 2008 brine well collapse. Numerous subsidence features with 8-month subsidence of 20-40 mm were interpreted in the Carlsbad Mining District study area. Some of these subsidence features underlie infrastructure, including a highway, railroad, and pipeline.