Just after 9.00 pm on Thursday 8 September 2011 the city of Nijmegen in the east of The Netherlands was shaken by a small earthquake. The epicenter of the quake was about 11 km so the southeast of the city, on the German border. The quake was recorded as having a magnitude of 4.2 on the Richter Scale and having occurred at a depth of 14.3 km by the United States Geological Survey and as having a magnitude of 4.3 on the Richter Scale and having occurred at a depth of 10 km by the Centre Sismologique Euro-Méditerranéen. This is a small quake, but very shallow, and it was felt across most of The Netherlands, and in neighbouring Germany as far east as Dortmund. No casualties or significant damage have been reported.
Map from the Centre Sismologique Euro-Méditeranéen, showing the epicenter of the quake (purple star) and the areas where it was felt. Larger circles indicate more people reported feeling the quake, and the colour indicates how severe the shaking they reported was.
Although The Netherlands is not noted for its seismic activity, the eastern part of the country, along with neighboring areas of Germany are part of the Lower Rhine Graben, an area of rifting associated with the uplift of the Alps and the collision of Africa with Europe. Essentially (and this is rather simplified) Europe to the east of the the Graben is being pushed northeastward by the northward movement of Africa. This stretches the crust and lithosphere on the Graben, causing it to thin and creating a long rift valley, which the River Rhine follows.
Simplified diagram showing a cross section through the Rhine Graben. The thinning of the lithosphere on the Graben causes a rift valley at the surface and an uplift in the asthenosphere bellow. In theory this could eventually develop into a full oceanic rift, with new crust being formed, but in this case it is unlikely.
This rifting leads to the occasional small earthquake in the region, though these are more common at the German end of the Graben, the most recent being the Koblenz Earthquake of February this year (2011), which like this quake caused no significant damage. Earthquakes in the Netherlands and western Germany have also occasionally been attributed to the activities of coal miners and drilling for natural gas.
If you felt the quake you can report it to the Royal Netherlands Meteorological Institute here, the Centre Sismologique Euro-Méditerranéen here and the United States Geological Survey here.
See also Earthquake in the Gulf of Corinth, Torino (Turin) rocked by mild earthquake and Earthquakes on Sciency Thoughts YouTube.
