The Dependence on the Moho Depth of the b-Value of the Gutenberg-Richter Law

We investigate the dependence of the Gutenberg-Richter b parameter on the crustal thickness quantified by the Moho depth, for nine different regional catalogs. We find that, for all the catalogs considered in our study, the b-value is larger in areas presenting a thicker crust. This result appears in apparent contradiction with previous findings of a b decreasing with the focal depth. However, both the results are consistent with acoustic emission experiments, indicating a b-value inversely proportion to the applied differential stress. Our results can be indeed interpreted as the signature of a larger stress concentration in areas presenting a thinner crust. This is compatible with the scenario where postseismic deformation plays a central role in stress concentration and in aftershock triggering.