Geophysical Mapping of Shallow Rock Salt at Borabue, Northeast Thailand

Abstract

In the northeast of Thailand, many swamps and lakes show evidence of rock salt dissolution, with attendant environmental problems due to saline groundwater and soil salinization. The knowledge of the depth and structure of the rock salt would be useful to achieve a better understanding of the impact of its dissolution on the environment and to facilitate effective land management strategies. Geophysical methods can provide key subsurface information. Four seismic refraction profiles and three electrical resistivity tomography profiles were carried out between Nong Bo and Nong Pong reservoirs in the salt‐affected Borabue district of Maha Sarakham province. The seismic results indicate the top of shallow rock salt beneath Nong Bo reservoir as a diagnostic zone of high P‐wave velocity >3400 m/s at depths >20 m. The electrical resistivity tomography investigation shows electrical resistivity values ≳5 Ωm at similar depths, indicative also of shallow rock salt. Zones interpreted to be saline groundwater are electrically conductive, identified by electrical resistivity values ≲5 Ωm in the electrical resistivity tomography images. The combined seismic–electrical resistivity tomography interpretation suggests that shallow rock salt lies beneath the reservoirs and ponds in the Borabue district but does not appear to form a continuous body between the two largest reservoirs.

Electrical resistivity tomographic detection of the hidden Thakek fault, Northeast Thailand

“…It is suggested that faulting controls flow diversions of the Mekong River, rather than salt tectonics, because fault traces are evident in the older rock formations of the Laos region, rather than the younger rock salt formations. While the Mahasarakham evaporite formation is widely distributed at various depths across northeast Thailand, salt movements usually form structures of circular shape (Sarntima et al, 2019) rather than the long lineaments that are found in the northeast Khorat plateau.…”