Lake Vättern is located in southern Sweden and is the second largest lake in the country.  Geophysical mapping and geological coring show striking deformation structures in the soft sediment accumulated on the lake floor. The bottom sediments have drastically been bent downwards in response to vertical tectonic displacements below the lake floor. The vertical displacements reach in places as much as 13 m. The new geological and geophysical data suggest that an earthquake took place in Lake Vättern with an estimated seismic moment magnitudes of about 7.5. Analysis of pollen in sediment infillings of the mapped collapse structures suggest that this major seismic event occurred at about 11 500 years BP. We suggest that this seismic event is related to the rapid release of ice-sheet load of the area following the deglaciation.

Article in Geology, currently available online as “Pre-Issue Publication”:
Major earthquake at the Pleistocene-Holocene transition in Lake Vättern, southern Sweden
Martin Jakobsson¹, Svante Björck², Matt O'Regan¹, Tom Flodén¹, Sarah L. Greenwood¹, Henrik Swärd¹, Arne Lif¹, Linda Ampel¹, Hemin Koyi³, and Alasdair Skelton¹
Open Access PDF: http://geology.gsapubs.org/content/early/2014/03/17/G35499.1.full.pdf+html

¹Department of Geological Sciences, Stockholm University, 106 91 Stockholm, Sweden
²Department of Geology, Lund University, Sölvegatan 12, 223 62 Lund, Sweden
³Department of Earth Sciences, Uppsala University, 752 36 Uppsala, Sweden

Field campaigns were carried during 2008, 2012 and 2013. The most recent multibeam surveys in 2013 were done with the Department of Geological Sciences survey vessel RV Skidbladner. The first field season in 2008 was supported by the Bolin Centre for climate Research at Stockholm University. We are grateful to Asera Mining AB for providing us with the opportunity to use their drilling platform to core in 2012. County Administrative Board Jönköping, is thanked for supporting the project. The Lake Vättern research is continued with support from the Swedish Geological Survey (SGU) and within the Research School focusing on Natural Hazards supported by the Swedish Research Council (VR).