Relation between seismicity and tectonic structures offshore and onshore Nordland, northern Norway

A temporary network of 27 seismic stations was deployed from August 2013 to May 2016 along the coast of Nordland, northern Norway, where northwestern Europe’s largest earthquake of magnitude 5.8 over the last two centuries has occurred. The NEONOR2 project aimed to improve our understanding of neotectonic movements, stress regime and the overall seismicity pattern in Nordland and the adjacent offshore areas. From the data retrieved from the temporary NEONOR2 deployment and the permanent stations of the Norwegian National Seismic Network, nearly 1250 earthquakes were located in the study area. During the monitoring period, the seismic activity in Nordland was mostly sporadic, but in some areas it was clearly episodic, especially to the west of the Svartisen glacier where an earthquake swarm with several hundred small seismic events was recorded from April 2015 until March 2016. The shallow swarm activity could possibly be partly related to the changes in the glacier mass and groundwater conditions. During the monitoring period, no earthquakes were recorded along the prominent Bivrost transfer zone, on the Trøndelag Platform and in the larger Vestfjorden Basin area, and it could therefore be concluded that these areas are aseismic; however, only three years of monitoring in such areas of low deformation rates is not enough to make strict conclusions. The observed lack of seismicity in the area generally confirmed earlier observations, though in this case with much more improved new data. The observations onshore provided clear indications of seismic activity along several previously unknown structures and well-defined lineaments trending NE–SW and NNW–SSE to the southwest of Svartisen, while a migration of the seismicity on some of these features was also recorded.

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