GEOPHYSICAL STUDIES FOR HAZARD DELINEATION IN SALT MINE ENVIRONMENTS.

Salt mines areas are known to be very dynamic environments as a consequence of salt rock ability to expand, contract and even "flow" (plastically flow) in certain stress and pressure conditions. As the sodium chloride is a high demanded resource since ancient times, old salt mining works are documented to have been executed even in areas nowadays exploited. The lack of precise location of ancient mine entrances and abandoned underground fieldwork locations poses severe problems to current mining activity, as well for other types of land use. Sinkholes, landslides, induced seismicity and eruptions of pressured salt brines springs are among the most common geological hazards associated to salt mining activities. Geophysics is known to play an important role in rock mineral exploration due to the capability of geophysical methods to explore the specific structures of geological formations or the rocks petrophysical properties. The same techniques of investigation, adequately adapted to the site specific requirements and targets, can be used for hazard delineation in nowadays exploited or in old mine areas. For hazard assessment, several studies which implied the use of gravity and resistivity prospection methods have been executed in high risk zones of a salt mine. The studied mine area is a joint between ancient exploitation zones still undiscovered, already collapsed salt mines or recently exploited and abandoned ones, placed in active mining areas. The complex salt tectonics, the presence of land instability areas and lakes with salty water (formed after the collapse of old mines roof), the presence of platforms covered with thick concrete layers and the recent constructed industrial buildings, created a challenging environment for the geophysical prospection. Despite the field impediments, the employed geophysical methods proved to be very useful for hazard delineation in salt mine areas. Gravimetric maps revealed the cause of a building subsidence, the data processing allowing the characterization of the buried hazardous source. The resistivity geoelectrical measurements (VES and ERT) revealed old mine shafts, abandoned salt exploitation rooms displaying broken roofs, fractures affecting the entire salt deposit and neighboring geological formations. Through the use the mentioned geophysical methods it was possible to characterize this very unstable industrial area. [ABSTRACT FROM AUTHOR]