Probabilistic Seismic Hazard Assessment of Sweden

Sweden is a low-seismicity, stable continental region where seismic hazard assessment is non-trivial. Diffuse seismicity, low seismicity rate, few large magnitude earthquakes and little strong motion data makes it difficult to estimate recurrence parameters and determine appropriate attenuation relationships. Here we present a probabilistic seismic hazard assessment of Sweden based on a recent earthquake catalogue which includes earthquakes with magnitudes ranging from -1.4 to 5.9. The large number of events enables recurrence parameters to be calculated also for smaller source areas, in contrast to previous studies, and with less uncertainty. We use recent ground motion models developed specifically for stable continental regions, including Fennoscandia, and calculate hazard using the OpenQuake engine. The results are presented in the form of mean peak ground acceleration (PGA) maps at 475 and 2500 year return periods, hazard curves for four seismically active areas in Sweden and deaggregation for the area of highest hazard. We find the highest hazard in the northernmost part of the country, in the post-glacial fault province. This is in contrast to previous studies, which have not considered the high seismic activity on the post-glacial faults. We find relatively high hazard along the northeast coast and in southwestern Sweden, whereas the southeast and the mountain region to the northwest have low hazard. For a 475 year return period we estimate the highest PGAs to be 0.04 0.05g, in the far north, and for a 2500 year return period it is 0.1-0.15g in the same area. Significant uncertainties remain to be addressed with regards to the intraplate seismicity in Sweden and surroundings, such as the homogenization of magnitude scales, the occurrence of large events in areas with little prior seismicity and the uncertainties surrounding the potential for very large earthquakes on the post-glacial faults in northern Fennoscandia.