Delineation of dry and water-bearing underground karst caves using a multicomponent grounded-wire transient electromagnetic method

ABSTRACT Karst caves are classified as dry or water bearing, and accurate classification is crucial for their protection and development. However, established geophysical methods are unable to delineate their properties, especially at large burial depths. We develop a grounded-wire transient electromagnetic method to observe multiple electromagnetic fields and characterize karst caves. We conduct a forward simulation of the horizontal electric field and the time derivatives of the vertical magnetic fields for dry and water-bearing karst caves. Water-bearing karst caves containing clays exhibit induced polarization effects. Dry karst caves indicate a sign reversal in the horizontal electric field response without distorting the time derivatives of the vertical magnetic field response. The difference between the sign reversal of the horizontal electric field and the time derivatives of the vertical magnetic field can be used to determine the characteristics of underground karst caves. When a sign reversal is only induced in the horizontal electric field, the underground karst caverns are likely to be dry. Simultaneous sign reversals of the horizontal electric field and the time derivatives of the vertical magnetic fields indicate water-bearing karst caverns. The results of these theoretical simulations are verified through a field survey in the Tonghua Cave, Jilin Province, China. This study provides a viable technical solution for the detection of underground karst caves, particularly those with large burial depths, and for classifying them as dry or water bearing.