GNGTS 2022 - Atti del 40° Convegno Nazionale

GNGTS 2022 Sessione 1.3 155 Fig. 1 - Results of the numerical tests on dry granite rheology: (A-B) strength (MPa) and (C-D) viscosity (Pa s) variation with depth, using three different values of strain rate and the (A and C) ‘warm’ and (B and D) ‘cold’ geotherm as input parameters. Light blue ellipses show the range of the BDT depth. See main text for further explanations. expressed in term of strength variations, to the input temperatures and strain rate. We can further notice that the ranges of the depth to the BDT tend to increase for the ‘ cold ’ geotherm and highest strain rate values (Fig. 1B), while the BDT temperature is more sensitive to the input strain rate and varies within a relatively narrow range. Despite the differences in the strength envelopes, related to the change of the input parameters, we found that the mean values of the effective viscosity at the depth of the BDT remains almost constant for the same strain rate value. An increase by two orders of magnitude in strain rate results in approximately the same amount of decrease in the mean viscosity at the BDT (Figs. 1C-D). At the same depth, the mean value in the reduction of Q s