Comparison of Interferometric Synthetic Aperture Radar (InSAR)-Derived Subsidence Time Series with Ground-Based Estimates of Sinkhole Activity, West-Central Florida, USA

West-central Florida is considered the “sinkhole alley” due to its high rate of sinkhole activity. Sinkholes in this region are usually formed from the erosion of overlying soil and sediment into open fissures of dissolved limestone bedrock. Since sinkholes are one of the leading natural disasters in west-central Florida precursory detection is crucial to alleviate risks of property damage. Detection of surface subsidence is possible using the Interferometric Synthetic Aperture Radar (InSAR) method. We examine the relationships between two-year long InSAR time series from persistent scatterers that show subsidence, and nearby ground-based measures of sinkhole activity or vulnerability. In particular we hypothesize that the degree of subsidence will correlate with both the raveling index (RI) and sinkhole resistance ratio (SRR) of the location, where the higher the index and lower resistance ratio the faster the subsidence velocity. The raveling index is a measure of the lengths of zones of low standard penetration test (SPT) blow count N-values. Low N-values are interpreted by engineers as indicators of loose soil or voids, and may be associated with past or present sinkhole activity and indicative of the presence of zones of downward flux of sediments. The sinkhole resistance ratio is an advancement of the raveling index, in that, it includes the reciprocal of the raveling index and soil strength parameters from cone penetrations tests (CPT). This hypothesis will be tested by statistically analyzing the correlation of local RIs and SRRs to nearby InSAR-derived velocities