A secondary sludge flow hazard induced by shallow-source seismic activity in karst mining area, Guangxi, South China: localized karstification in anticline

On the 16th of June 2013, a small-magnitude, shallow-source seismic activity just occurred at a karst mining area. No serious ground damage occurred, but it induced a secondary geological hazard. The wastewater and sludge leaked from the mining water reservoir which caused a great economic loss and groundwater contamination through multilevel underground karst channels. The seismic swarm was located along the Youjiang fault, an active fault zone whose kinematics is controlled by the regional tectonic stress field with NW300° compression and NE30° extension. The tectonic fractures are sealed by calcite, and stylolites have permeabilities of less than 0.01 mD. The localized intensive karstification occurred at the core of Yalang anticline, which is the result of a local extension stress environment and hydrogeological conditions. The seismic activity in the study area is not strong enough to cause ground destruction, but did alter the flow dynamics of groundwater. The seismic activity may have caused a temporary high pressure fluid in the fault zone. The karst system blocked by sediments can be dredged by the fluid pressure. Then, the karstification of limestone massif could be re-activated.