The Kattegat Sea separates Denmark from Sweden, north of the Islands of the Straits of Denmark. On Monday 6 August 2012, slightly before 5 am local time (slightly before 3 am GMT), an Earthquake took place 5.8 km beneath this sea, according to the United States Geological Survey, who measured the quake as 4.4 on the Richter Scale. This is small enough that it is highly unlikely to have caused any damage, although it was reportedly felt by people in both Sweden and Denmark.
Map showing the location of the 6 August 2012 quake. USGS.
Earthquakes are rare in Denmark, southern Sweden, and the waters between them, and those that do occur tend to be small, which makes the causes hard to determine. The entire of Europe is being pushed eastward by the expansion of the Atlantic Ocean and northward by the impact of Africa from the south, though these are remote from the Kattegat. There are lesser areas of expansion beneath the North Sea and Rhine Valley, both of which will presumably have some effect on southern Scandinavia. Finally their is glacial rebound; until about 10 000 years ago much of northern Europe was covered by a thick layer of ice. This pushed the rocks of the lithosphere down into the underlying mantle, and now that the ice is gone these rocks are springing back up, albeit very slowly, a process which is not smooth as rocks tend to stick to one-another, and which therefore causes the occasional small Earth tremor.
See also Magnitude 6.2 Earthquake north of Norway, Southwest Poland hit by Earthquake, Zurich shaken by mild Earthquake, Earthquake in the Netherlands and Earthquakes on Sciency Thoughts YouTube.
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