Although the Netherlands seems to be a tectonically quiet area, a number of fault activities have been shown in the past. The latest strong earthquake, the 1992 Roermond earthquake (5.4 on Richter scale), had its epicenter close to the Limburg city of Roermond. The south of the Netherlands is topographically higher and is linked to the geology of the Ardennes and the London-Brabant Massif. The Lower Rhine Graben, part of the European Cenozoic Rift System, which has been tectonically active since the Oligocene, affects the southwestern part of the Netherlands.