Control of tectonic inheritance on continental intraplate strain rate and seismicity
Résumé
Present-day deformation and seismicity of continental lithosphere are characterized by a first-order dichotomy between Plate Boundary Zones (PBZ) and Stable Continental Regions (SCR). Whereas the former are associated with high strain and seismicity rates, the latter tend to remain un-deformed, except in localized regions of higher strain and seismicity, commonly related to fossilized paleo-PBZ acting as locally weaker domains. Because of their low amplitudes, these intraplate strain and seismicity rates are particularly difficult to measure and characterize. In this study, we propose a simple model to explain and quantify first-order continental strain rate variations, focusing on intraplate regions. Assuming near-failure equilibrium on 1D lithosphere profiles, we derive steady-state strain rates driven by tectonic forces as a function of rheological models that include new strain-weakening rheologies in order to simulate tectonic inheritance. Within this framework, inherited strain-weakening plays a fundamental role in allowing for and explaining strain and seismicity concentration in intraplate weak zones: our model predicts strain rates in intraplate weak zones up to two to three orders of magnitude higher compared to stable cratons due to the effect of tectonic inheritance on rheology weakening. These model predictions are in agreement with empirical estimations in intraplate regions and can provide a conceptual framework for characterization of SCR strain and seismicity rates.