Identification of sinkhole origin using surface geophysical methods, Dead Sea, Israel

Abstract

The western and eastern Dead Sea (DS) shores are hit by intensive sinkhole collapse during the last 30 years. The first researchers have considered a piping model of sinkhole formation, based on washing out fines by underground flows. Then, it was proved by numerous boreholes and seismic refraction surveys that sinkholes along western shore are caused by dissolution of buried salt layers and collapse of the surface into dissolution caverns. However, signs of piping and subsurface flows were observed in some sinkhole sites. In this paper, we show that robust identification of sinkhole origin can be achieved when proper geophysical methodologies and their application are used. We consider Newe Zohar site located in the southern part of the Dead Sea in order to analyse different signs of sinkhole formation models using various geophysical methods. The Seismic refraction method (SRFR), enables us to discover the salt layer based on longitudinal wave velocity Vp; the Multichannel Analysis of Surface Waves (MASW) method allows to determine the salt layer properties (rigidity) based on shear wave velocity Vs; finally, the Time Electromagnetic (TEM) method allows us to evaluate the degree of aggressiveness of groundwater with respect to salt, based on bulk resistivity values. Here we analyse competitive models of sinkhole formation and suggest geophysical methods to determine the subsurface geomorphology. We show that various geophysical methods should be applied in concert to explore the subsurface for the occurrence of salt, as well as understanding sinkhole formation processes. The underlying voids along the Dead Sea are shown to form primarily by salt dissolution, with some cases of additional piping. Applying the right geophysical parameters for groundwater and salt sediments classification proves to be crucial for understanding the subsurface geomorphology.