Investigation of Subsurface and Geological Structures Contributing to Collapse Sinkholes in Covered Karst Terrain, Northeast Thailand

This study focuses on covered karst terrain situated in Phu Pha Man District, Khon Kaen Province, Northeast Thailand, where records of collapse sinkholes are limited. Here, we investigate the subsurface characteristics and potential causes of sinkhole formation within this area using geophysical methods, hydrogeological techniques, and precipitation analysis. We collected field data by measuring groundwater levels, and conducting electrical resistivity tomography (ERT) surveys. We identified eight cover-collapse sinkholes of various shapes and sizes. Analysis of the groundwater flow indicated that the predominant flow direction runs from north to southeast. Examination of rainfall data showed a progressive increase in total rainfall on a yearly basis, with a significant precipitation event preceding the initial occurrence of sinkholes. The ERT results revealed the presence of highly resistive bedrock, water-saturated layers, and potential cavities. Notably, the tomograms indicated variations in resistivity values, suggesting the presence of irregular surfaces of limestone bedrock and weathered zones as characteristics of karst settings. Intense precipitation is a possible dominant trigger for the formation of the sinkholes. This study contributes to understanding sinkhole formation in karst environments and provides key information for hazard mitigation, not only in the Phu Pha Man District but also in areas with similar geological settings.