Distributed faulting following normal earthquakes: reassessmentand updating of scaling relations

Abstract. Coseismic surface faulting is a significant source of hazard for critical plants and distributive infrastructures; it may occur either on the primary fault, or as distributed rupture on nearby faults. Hazard assessment for distributed faulting is based on empirical relations which, in the case of normal faults, were derived almost 15 years ago on a dataset of US earthquakes. We collect additional case histories worldwide, for a total of 21 earthquakes, and we calculate the conditional probability of distributed faulting as a function of distance from the primary fault. We found no clear dependency on the magnitude nor the time of occurrence of the earthquakes, but our data consistently show a higher probability of rupture when compared to the scaling relations currently adopted in engineering practice. We derive updated empirical regressions and show that results are strongly conditioned by the averaging of earthquakes effectively generating distributed faulting at a given distance and those which did not generate faulting; thus, we introduce a more conservative scenario, which can be included in a logic tree approach to consider the full spectrum of potential ruptures. Our results can be applied in the framework of probabilistic assessment of fault displacement hazard.