The Influence of Lithology and Fault Source Volume on the Magnitude–Frequency‐Distribution of Earthquakes

Abstract 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.