Effect of Stress Interaction on the Probability of Occurrence of Characteristic Earthquakes in Southern Apennines

It is commonly accepted that neighboring faults can interact, affecting the probability of occurrence of future earthquakes. A large earthquake can change the static stress on surrounding faults up to several hundred kms promoting their rupture, and activating aftershock sequences. In several cases a clear correlation has been noted between the pattern of positive Coulomb stress change and the increase of the local occurrence rate density, both in normal and in strike fault systems. In this study we compute the effect of stress change due to previous historical earthquakes on the probability of occurrence of future earthquakes on neighboring faults. Following the methodology developed in the last decade (e.g. Parsons et al., JGR 2004) we start from the estimate of the probability of occurrence in the next 30 years for a characteristic earthquake on known seismogenic structures, based on a time-dependent renewal model. Then, a physical model for the Coulomb stress change caused by previous earthquakes on these structures is applied. The influence of this stress change on the occurrence rate of characteristic earthquakes is computed taking into account both a permanent (clock advance) and a temporary (state-and- rate) perturbation. We apply the method so developed to the computation of earthquake hazard of the main seismogenic structures recognized in the Southern Apennines region, for which both historical and paleoseismological data are available. This study provides the opportunity of reviewing the problems to be faced in connection with the estimate of the parameters of a renewal model in case of characteristic earthquakes characterized by return times that are longer than the time spanned by the available catalogues, and the concept of characteristic earthquake itself. The results show that the estimated effect of earthquake interaction in this region is small compared with the uncertainties affecting the statistical model used for the basic time-dependent hazard assessment.