We address the problem of seismicity in the intraplate area of northern Fennoscandia using the information on local events recorded by the POLENET/LAPNET seismic array. We relocate the seismic events, calculate a 3-D tomographic P wave velocity model of the uppermost crust and investigate a focal mechanism of the event. Our results demonstrate that the Baltic-Bothnia Megashear is an important large-scale, reactivated tectonic structure that has to be taken into account when estimating seismic hazard.

POLENET/LAPNET broadband seismic network was deployed in northern Fennoscandia 2007–2009. In our study we estimate the 3D architecture of the upper mantle beneath the network using high-resolution teleseismic P-wave tomography. Our study reveals a highly heterogeneous lithospheric mantle. The most significant feature seen in the obtained velocity model is a large elongated low-velocity anomaly beneath the crust, separating the three cratonic units that formed the region in the early Proterozoic.