The influence of tectonic regimes on the earthquake size distribution: A case study for Italy

We explore the hypothesis that the relative size distribution of earthquakes, or b-value, systematically depends on the style-of-faulting of seismotectonic zones. Because the b-value has been shown to be inversely proportional to stress, we expect to find b(thrust) < b(strike-slip) < b(normal). We test this expectation for the case of Italy. We first of all build a seismotectonic zonation model, consisting of 10 distinct tectonic zones. The faulting style of each zone is then characterized by the summed moment tensor of first-motion and full-waveform based focal mechanism. We calculate the b-value for each zone: the lowest values are obtained for reverse zones (0.75-0.81), highest for the normal (1.09), followed by the strike-slips (0.9-0.92). Our results suggest that b-values, which are a critical parameter in all seismic hazard assessments, should be set according to the local faulting regimes. In addition, seismotectonic zonation models should take b-value variations as one input. Copyright © 2010 by the American Geophysical Union.