Probabilistic seismic hazard assessment of Sweden

Assessing seismic hazard in stable continental regions such as Sweden poses unique challenges compared to active seismic regions. With diffuse seismicity, low seismicity rate, few large-magnitude earthquakes and little strong-motion data, estimating recurrence parameters and determining appropriate attenuation relationships is challenging. This study presents a probabilistic seismic hazard assessment of Sweden based on a recent earthquake catalogue, which includes a high number of events with magnitudes ranging from Mw -1.4 to Mw 5.9, enabling recurrence parameters to be calculated for smaller source zones than in previous studies and with less uncertainty. Recent ground motion models developed specifically for stable continental regions, including Fennoscandia, are used in the logic tree accounting for their uncertainty, and the hazard is calculated 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 and hazard curves for four seismically active areas in Sweden. We find the highest hazard in Sweden 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 relatively high seismic activity on the post-glacial faults. We also find hazard to be relatively high along the northeast coast and in southwestern Sweden, whereas the southeast of Sweden and the mountain region to the northwest have low hazard. For a 475-year return period we estimate the highest PGA values to be 0.04-0.06 g in the far north, and for a 2500-year return period it is 0.1-0.15 g in the same area. Much remains to be addressed in regards to the intraplate seismicity in Sweden, including the homogenization of small local magnitudes with large moment magnitudes, the occurrence of large events in areas with little prior seismicity and the uncertainties surrounding the potential for large earthquakes on the post-glacial faults in northern Fennoscandia.