Modelling tectonics and seismicity due to slab retreat along the northern Apennines thrust bel
Abstract
The northern Apennines (Italy) are considered an atypical orogen, because they include both an extensional and compressional domain as a result of slab retreat in absence of net convergence. Regional seismicity has been extensively studied, especially after the damaging 2012 Emilia sequence. However, how it relates to lithospheric-scale structure and dynamics, and what physical parameters are compatible with tectonic, geodetic and seismological observations, remains unclear. We study this complex geodynamical system with a 2D, tectonically realistic, visco-elasto-plastic seismo-thermo-mechanical (STM) modelling approach. Using several geological and geophysical constraints we design a high-resolution model of the present-day northern Apennines that is purely driven by buoyancy of the oceanic slab and crust. Temperatures, broadly based on a retreating subduction simulation, were varied in key areas. Results from the long-term evolution show protrusion and lithospheric delamination in the mantle wedge in case of a relatively high temperature and ductile lower crust rheology. This is needed to obtain a coeval spatial distribution and evolution of the observed extensional and compressional domains. Moreover, it provides a good match with interseismic deformation in terms of horizontal velocities and principal stress axes orientations. This suggests that slab delamination and retreat are compatible with the observed deformation. At the same time, these parameters also correctly reproduce seismicity on the external buried, internal normal, and range base thrust faults. Different experiments with increasing long-term runtime show activity shifting from the normal faults to the range base thrusts as the boundary between domains migrates. Decreasing fault friction transfers seismicity from the thrust front to the range base, where compressive normal stresses are lower. Deeper events beneath the thrust front are produced as extensional ruptures due to slab bending. However, unlike in observations, they are located below the Moho, suggesting that deep rheological layering in the foreland differs significantly from the models, or that focal depth estimates underneath the Po plain are consistently wrong.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.T33D0432D
- Keywords:
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- 8155 Plate motions: general;
- TECTONOPHYSICSDE: 8159 Rheology: crust and lithosphere;
- TECTONOPHYSICSDE: 8175 Tectonics and landscape evolution;
- TECTONOPHYSICS