Seismic Hazard and Earthquake Source Parameters in the North Sea

Abstract

Contemporary seismicity delineated in the North Sea by modern instrumental seismograph networks, deployed and analysed most intensively since 1980, allows study of coseismic crustal deformation by integrating information on statistical seismic hazard and earthquake source parameters. The seismicity observed during 1980–86 in the North Sea shows four earthquakes exceeding local magnitude 4.0 ML, three of which are in the northern North Sea; none exceed 5.0 ML. The longer view of historical seismicity since 1900, needed to assess seismic hazard, shows 30 earthquakes of magnitude 5 or larger and extreme value analysis estimates an annual expection of 10-2 for an earthquake exceeding magnitude 6 anywhere in the North Sea. An upper bound to earthquake magnitude around 6.75 is compatible with evidence from other studies in and adjoining the North Sea: palaeoseismic data in Scotland has been interpreted as suggesting earthquakes of magnitude 6.5–7.0 in the last 10 years BP and the second Storegga slide in the northern North Sea has been associated tentatively with a magnitude 7 earthquake around 7 × 103 years BP. However, cumulative strain energy release diagrams applied to the historical seismicity indicate a current upper bound to magnitude of 6.44.