Isodepth temperature maps (obtained from the thermal model by Schintgen et al. 2015). Temperature (°C) evaluated at (a) 1,000, (b) 2,000, (c) 3,000 m, (d) 4,000, (e) 5,000, and (f) 6,000 m below mean sea level. Gray and light gray zones indicate the Hunsrück and Ardennes-Eifel blocks, respectively. Squares indicate major cities, and full circles indicate towns of at least several thousand inhabitants.