Monitoring ground subsidence induced by salt mining in the city of Tuzla (Bosnia and Herzegovina)

Salt mining induced ground subsidence is a major hazard in the city of Tuzla (Northeastern sector of Bosnia and Herzegovina) and its surroundings since 1950, when solution mining of salt deposits by boreholes began. An analysis of the large (and never before processed) amount of topographical data collected during two periods: from 1956 to the Balkan War, and from 1992 to 2003 has been made. The analysis reveals a cumulative subsidence as high as 12 m during the whole period, causing damage to buildings and infrastructures within an area that includes a large portion of the historical town. Human-induced subsidence, (with rates up to 40 cm/year in the most developed area), has been investigated to recognize the areas affected by the sinking phenomenon and to produce a subsidence hazard. The time series of topographical observations have been enlarged by conducting new surveys in the urban area by modern space-geodesy methodologies, such as static relative GPS (Global Positioning System) and high resolution satellite imageries. The GPS monitoring started in 2004 and detected a decrease in the subsidence rates to 20 cm/year related to the reduction of salt exploitation. There is close correlation between the average subsidence rate and the annual amount of salt extracted.