A provisional seismic source zonation of Iceland for the ESHM20 based on new physics-based bookshelf fault system models and a new revised earthquake catalogue

Abstract

The earthquake hazard in Iceland is highest in its two transform zones, the South Iceland Seismic Zone in the South and the Tjörnes Fracture Zone in the North and the reliable probabilistic seismic hazard assessment (PSHA) is the prerequisite for the codified aseismic design of structures and mitigation of seismic risk. The three fundamental aspects of a reliable PSHA, the proper specification of the seismic sources, in particular in the transform zones, their activity rates, and the use of acceptable forms of ground motion models that characterize the rapid attenuation of Icelandic strong-motion, need to be based on the latest state-of-the-art information and methods. In this study, we present a new and provisional subdivision of Iceland into seismic area-source zones on the basis of new physics-based fault system models as well as parameter set for each zone based on new revised and harmonised earthquake catalogue for Iceland. The zonation is guided by the systematic spatial distribution of the predominant types of earthquake faulting mechanisms in Iceland, consistent with the volcanic and transform zones in the country. Moreover, the new physics-based estimates of activity rates in the transform zones effectively explain the historical seismicity and allow the specification of subzone activity rates. On the basis of this new zonation finite-fault earthquake catalogues can be simulated for long-time intervals that are consistent with the time-independent estimates of seismicity. The provisional seismic zonation model can therefore both serve as the basis for the revision of the PSHA of Iceland using conventional engineering approaches and lays the foundation for physics-based earthquake rupture simulation approaches to the time-independent PSHA. For the time being however, this provisional model has been provided to the harmonized efforts of PSHA in Europe (ESHM20).