Near-surface earthquakes in the Baltic shield, notably Sweden

A recent series of Swedish earthquakes at a focal depth not exceeding 2–3 km, the largest with I_O = V + (MSK scale) andM_L = 3.2 shows that relatively strong seismic activity can occur in the uppermost part of the Baltic Shield. During the last 15 years several near-surface earthquakes have occurred in this region, as indicated by recorded Rg-waves and/or macroseismic data. Many events are located along the coast of central Sweden, suggesting a seismic belt of minor, near-surface activity, which should be considered in connection with the radioactive waste storage in the Swedish bedrock. The appearance of Rg, common in seismic records of explosions and rockbursts, is not a sufficient discriminator between artificial events and earthquakes.