GNGTS 2022 - Atti del 40° Convegno Nazionale

156 GNGTS 2022 Sessione 1.3 Fig. 2 - Results of the numerical tests on dry granite rheology: (A-B) Q s and (C-D) Q s reduction (%) 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. shows a direct proportionality with the imposed strain rate values, while it seems to be less affected by changes in the other input parameters (Figs. 2C-D). Therefore, reduction in Q s at the BDT is characterized by a specific order of magnitude for each strain rate value (10 -12 , 10 -10 , and 10 -8 % for strain rate equal to 10 -17 , 10 -15 , and 10 -13 s -1 , respectively). As expected, below the BDT the yield strength reduces to negligible values (< 10 MPa) faster for hydrated rheology and when the ‘ warm ’ geotherm and lowest strain rate value are used (Figs. 2A). In a similar fashion, also the viscosity values and reduction in Q s at the base of the crust vary by some orders of magnitudes, depending on the input parameters. On the other hand, mafic rheologies deform prevalently in brittle conditions and their