Original Article

Journal of Seismology

, Volume 15, Issue 4, pp 599-611

Open Access This content is freely available online to anyone, anywhere at any time.

The seismotectonics of western Skagerrak

  • Mathilde Bøttger SørensenAffiliated withDepartment of Earth Science, University of Bergen Email author 
  • , Peter H. VossAffiliated withGeological Survey of Denmark and Greenland - GEUS
  • , Jens HavskovAffiliated withDepartment of Earth Science, University of Bergen
  • , Søren GregersenAffiliated withGeological Survey of Denmark and Greenland - GEUS
  • , Kuvvet AtakanAffiliated withDepartment of Earth Science, University of Bergen

Abstract

The seismically active Skagerrak region in the border area between Denmark and Norway has traditionally been associated with uncertain earthquake locations due to the limited station coverage in the region. A new seismic station in southern Norway and a recent update of the earthquake database of the Danish National Network have led to a much more complete and homogeneous data coverage of the Skagerrak area, giving the possibility of improved earthquake locations in the region. In this study, we relocate earthquakes in the Skagerrak area to obtain a more exact picture of the seismicity and investigate well-recorded events to determine the depth distribution. Hypocenter depths are found to be generally in the range 11–25 km. Furthermore, new composite focal mechanisms are determined for clusters of events with similar waveforms. Results indicate that the Skagerrak seismicity is associated with shallow, crustal faults oriented in the NS direction south of the Sorgenfrei–Tornquist Zone (STZ) as well as with the STZ itself. Mainly reverse faulting mechanisms along NE–SW oriented faults indicate maximum horizontal compression in the NW–SE direction. This is in agreement with World Stress Map generalizations, most likely associated with ridge push forces from the mid-Atlantic ridge, though modified probably by local crustal weaknesses.

Keywords

Skagerrak Seismotectonics Seismicity Fault plane solution Hypocenter depth Sorgenfrei-Tornquist zone