In the German national annex of Eurocode 8 (EC8) "Design of structures for earthquake resistance", the influence of local ground conditions on earthquake impact has to be taken into account. Generally, the shallow structure is classified as a combination of one of three geological subsurface classes and one of three subsoil classes in the national annex. For the determination of the subsoil class, the rock mass down to a depth of 30 meters is considered. For the determination of the geological subsurface class, the structure below 30 m depth down to several hundred meters is considered.
As part of the recent update of the national annex of EC8, the map of geological subsurface classes, which is a part of the code, was revised. For the new map, the methods of geological 3D modelling were used for the first time. Based on data from the geological 3D models of the federal states Baden-Württemberg, Bavaria, Hesse, North Rhine-Westphalia, Rhineland-Palatinate, Saxony, Saxony-Anhalt, and Thuringia, the thicknesses of Quaternary and Tertiary sediments were determined first. Based on these thicknesses, the geological subsurface classes "R" (rock), "T" (shallow sediment basins), and "S" (deep sediment basins of more than 100 m thickness) were assigned. The geological subsurface classes were presented on a grid with a cell size of 1 km x 1 km. Compared to the previous assignation of geological subsurface classes, in which geological structures of less than 20 km extension or diameter could not be considered, a significantly higher spatial resolution was achieved.