The Storfjorden, Svalbard, 2008–2012 aftershock sequence: Seismotectonics in a polar environment

•Seismotectonic study of a long aftershock sequence in Svalbard, European Arctic•Relative locations of aftershocks and moment tensor solutions•Activation of unmapped, NE–SW oblique-normal fault and secondary structures•Migration of aftershocks signifying possible stress triggering•Important implications for earthquake hazard assessment in Svalbard

A long, complex aftershock sequence has followed an Mw 6.1 mainshock in February 2008, in Storfjorden, Svalbard. Relatively located aftershock epicenters and focal mechanisms from moment tensor inversion suggest that the series took place along a NE–SW trending and steeply SSE dipping oblique-normal fault, with the total aftershock extent exceeding the mainshock rupture. The magnitude of the mainshock and the duration of the aftershock activity render the Storfjorden sequence important in terms of earthquake hazard assessment in the Svalbard region. We have evaluated all involved uncertainties and combined seismological information with background knowledge for the area, in order to achieve as sound a seismotectonic interpretation as possible. Our results clearly indicate that the activity in Storfjorden should be attributed to a previously unknown tectonic structure. In addition, there are indications of activation of secondary structures and possibly of stress triggering. These new findings affect our understanding of the region's earthquake potential.