Locating Karstic Void using Resistivity and Gravity Methods in Gua Musang, Kelantan, Malaysia

Abstract

Gravity and resistivity are geophysical methods used to delineate the subsurface of the Earth. The interpretation of subsurface layers can be useful for exploration purposes and detecting anomalies that could lead to hazardous events. In this study, a CG-5 Autograv Scintrex was used to measure and collect gravity data where gravity points were calculated at 5 to 10 meters between each station. This method is conducted in a looping manner whereby, after every three (3) hour interval, the gravity points are tied to the base for the closing of the loop. These data points were then transferred into a computer for further processing and interpretation. Similarly, the resistivity method investigates variations of electrical resistance by causing electrical current to flow through the subsurface using wires connected to the ground. In this research, a dipole-dipole protocol was implemented to a 200-meter-long survey line with each line representing 100 meters from the center. The electrodes were planted every 5 meters across 6 survey lines using ABEM Terrameter SAS 4000. The obtained resistivity data were also transferred into the computer for further processing using the RES2DINV programme to create a resistivity pseudosection model. The model was further interpreted to locate the karstic void from the difference in resistivity value at different depths. The combined results from both gravity and resistivity methods gave a more accurate representation of the Earth's subsurface layers which in turn enable the location of the void to be pinpointed more accurately.