Along the major thrust fault of the Variscan orogeny, there are over 30 thermal springs in Aachen and Burtscheid. Additionally, the subsurface of Aachen is traversed by numerous active faults that belong to the Rurgraben fault system, which has been responsible for numerous earthquakes in the past, including the 1756 Düren earthquake and the 1992 Roermond earthquake, which was the strongest earthquake ever recorded in the Netherlands.