Groundwater changes in relation to seismic activity: a case study from Eskipazar (Karabuk, Turkey)

The reported study contributes to research on earthquake prediction. Between 2007 and 2009, changes were observed in two geothermal and mineral springs located in Eskipazar (∼3–5 km to the north of the North Anatolian Fault Zone) in Turkey, in relation to small-magnitude earthquakes. During pre-seismic and post-seismic activities, variations were observed in the hydrogeological parameters of the spring waters. Temperature increases of 0.4–1°C were measured in one of the springs prior to three different earthquakes. There was a slight increase in the spring discharge with respect to the first earthquake, which occurred closest to the spring. This led to a reduction in electrical conductivity (EC), total dissolved solids (TDS), Ca, HCO₃, δ¹³C, Al, Mn, and Fe concentrations in the spring water, whereas tritium and Se values increased. Several days before the third earthquake, which occurred at a shallower depth, a decrease was observed in the discharge, which led to a reduction in tritium, δ¹³C and Si concentrations. These variations could be explained by changes in the mixing ratio of waters of different genesis, depending on changes in permeability, pore pressure, and flow paths of the aquifer due to regional stress changes.