Geophysical characterization of dissolution structures in urban settings in South Florida

Dissolution structures and sinkholes form when rocks and/or sediments move into a void space created through rock dissolution, that commonly develop in carbonate sediments like those found in South Florida. This can result in surface subsidence as shown by a gradual surface depression, however they remain hidden underground until the right conditions for a rupture occur. Accelerated use of groundwater and land use change in recent decades has caused an increase in the rate of sinkhole formation particularly in urban settings, making sinkhole collapse one of the leading natural disasters in Florida and a significant threat to important infrastructure. Detecting a sinkhole before collapse can be difficult since sinkholes often display unnoticeable surface changes. To assist with this problem, geophysical techniques such as ground penetrating radar (GPR), electrical resistivity imagining (ERI), and electromagnetic surveys are commonly used to image sinkhole characteristics beneath the surface and show potential for identifying dissolution structures conducive to sinkhole formation before collapse. In this work a set of case studies from urban settings in South Florida are presented that combine an array of geophysical methods with direct coring to show the ability of these methods to image high resolution contrasts in physical properties (i.e. cm) related to dissolution structures that may be potentially conducive to sinkhole collapse. This study shows the importance of the application of non-invasive geophysical methods as a first step towards identification and characterization of sinkholes and the potential for its monitoring by combining with time-lapse surveys.