Editing Aachen (section)

== Geology ==
[[File:Aachen Felsen St.Adalbert.JPG|thumb|Layered [[sandstone]] and [[claystone]] [[formation (stratigraphy)|formation]] from the [[Devonian]] period below St. Adalbert Church in Aachen]]

The geology of Aachen is very structurally heterogeneous. The oldest occurring rocks in the area surrounding the city originate from the [[Devonian]] period and include [[carboniferous]] [[sandstone]], [[greywacke]], [[claystone]] and [[limestone]]. These formations are part of the [[Rhenish Massif]], north of the High Fens. In the [[Pennsylvanian (geology)|Pennsylvanian]] subperiod of the [[Carboniferous]] geological period, these rock layers were narrowed and folded as a result of the [[Variscan orogeny]]. After this event, and over the course of the following 200 million years, this area has been continuously flattened.<ref>{{cite book |last1=Anderson |first1=Ernest Masson|editor1-last= Healy|editor1-first= David |year=2012 |title=Faulting, Fracturing and Igneous Intrusion in the Earth's Crust |issue=367 |volume=367 |publisher=Geological Society of London |isbn=978-1-86239-347-9 |issn=0305-8719}}</ref>

During the [[Cretaceous]] period, the ocean penetrated the continent from the direction of the [[North Sea]] up to the mountainous area near Aachen, bringing with it clay, sand, and chalk deposits. While the clay (which was the basis for a major [[pottery]] industry in nearby [[Raeren]]) is mostly found in the lower areas of Aachen, the hills of the [[Aachen Forest]] and the [[Lousberg]] were formed from upper Cretaceous sand and chalk deposits. More recent sedimentation is mainly located in the north and east of Aachen and was formed through [[tertiary]] and [[quaternary]] river and wind activities.

Along the major [[thrust fault]] of the [[Variscan orogeny]], there are over 30 [[thermal spring]]s in Aachen and [[Burtscheid]]. Additionally, the subsurface of Aachen is traversed by numerous [[active fault]]s that belong to the Rurgraben fault system, which has been responsible for numerous earthquakes in the past, including the 1756 [[Düren]] earthquake<ref name="duerenEQ">{{harvnb|University of Cologne, Seismological Station Bensberg|2013}}.</ref> and the [[1992 Roermond earthquake]],<ref name="Roermond">{{harvnb|Geological Survey of North Rhine-Westphalia|2013}}.</ref> which was the strongest earthquake ever recorded in the [[Netherlands]].