The Swedish National Seismic Network at Upsala University, recorded a Magnitude 4.1 Earthquake close to the town of Kiruna in Swedish Lapland, slightly after 3.10 am local time (slightly after 1.10 am GMT) on Monday 18 May 2020. There are no reports of any casualties associated with this event, but it triggered a rockfall at the Kiruna Iron Mine, which has been closed as a precaution while an assessment of the stability of the site is assessed. The Earthquake was recorded as having a Magnitude of 4.9 by the United States Geological Survey, which would make the event the largest Earthquake ever recoded instrumentally in Sweden, however Swedish assessments of the event make it a once-in-a-decade event.
The approximate location of the 18 May 2020 Swedish Lapland Earthquake. USGS.
Earthquakes are rare in Sweden, 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.
(Top) Simplified diagram showing principle of glacial rebound. (Bottom) The extent of glaciation in Europe at the last glacial maximum. Wikipedia.
Witness accounts of Earthquakes can help geologists to understand these events, and the structures that cause them. The international non-profit organisation Earthquake Report is interested in hearing from people who may have felt this event; if you felt this quake then you can report it to Earthquake Report here.
Follow Sciency Thoughts on Facebook.