Differences in earthquake size distributions for thrusts and normal faults: the case of Italy

The earthquake size distribution is characterized by an exponential function determined by the b-value parameter. Previous studies have demonstrated the dependence of the b-value on both the differential stress and tectonic settings. This study proposes a novel approach to categorize earthquakes based on the kinematics of interseismic geodetic strain rates and horizontal stress directions. When combined with other geological or geophysical information, incorporating stress directions and geodetic data enhances seismotectonic models, reducing arbitrariness in delineating seismic zones. Using the Italian peninsula as a case study, we observe a significantly larger b-value for extensional faults than thrusts, albeit with smaller differences than previously reported. Additionally, our findings reveal that the spatial fragmentation of uniform tectonic regimes can lead to inaccurate b-value estimates for single faults due to the undersampling of earthquake size distribution.