The influence of lithology and fault source volume on the Magnitude–Frequency-Distribution of earthquakes

The earthquake Magnitude-Frequency-Distribution is usually modeled with the Gutenberg-Richter law, where the b-value controls the relative rate of small and large earthquakes. b-value shows an inverse dependence on differential stress, it increases with fault roughness and in areas with fluid involvement in faulting. b-value analyses have been also applied to infer temporal evolution of the stress state along active faults or to discriminate between foreshocks and aftershocks. For the Mw 6.5 2016-2017 Central Italy seismic sequence, we show that: (a) away from the major earthquake faults, b-values are controlled by lithology and style of deformation; (b) the absolute number of the b-values depends on the adopted magnitude scale and catalog, but differences induced by lithology are preserved; (c) the selection of the fault source volume can strongly influence b-value changes in time, highlighting some complexities on the applicability of the b-value as fault stress meter.