Source parameters for earthquakes in the northern North Sea

A source parameter (focal mechanism) analysis has be en conducted for six recent earthquakes in the northern North Sea: one magnitude (ML) 4.3 event in the Viking Graben in 1982, one ML 4.6 event at Stord in 1983, and four smaller (ML 2.8-3.1) events further north in 1985. The Viking Graben earthquake shows oblique normal faulting consistent with NW-SE extensional tectonics, the Stord earthquake shows oblique thrust faulting consistent with E-W horizontal compression, while the smaller events further north (near 61.5°N, 4°E) are mostly of the strike-slip type with a NE-SW orientation of the compressional axis and a NW-SE orientation of the tensional axis. Within these parts of the North Sea and western Norway, the stress-generating situation is multifactional, with probably quite complicated interactions between long term tectonic causes of seismicity and more short term post-glacial rebound effects.