Do Plate Boundary Forces Drive Seismicity in Continental Interiors? Insights from a Study in Central-Western Europe
Abstract
The low, but non-negligible, level of seismicity in the stable continental interior of Western Europe is often interpreted as a result of the "far-field effects" of the Nubia-Eurasia oblique convergence further south in the western Mediterranean. Here, we try to understand to what extent this proposition holds. In particular, we seek to determine the level of intraplate deformation - in the bulk of the crust or localized on pre-existing faults - that is expected given such a tectonic setting. Indeed, current geodetic measurements indicate strain rates that are undetectable and lower than 10-9 yr-1 over most of intraplate Europe, with no indication on regional or local strain accumulation within the precision of the measurements. Yet, significant earthquakes (magnitude 5.5-6.5) do occur in intraplate regions, some of them being close to isostatic equilibrium (Ziegler and al, 2006), such as the Massif Armoricain (Bouin, 1799), Channel area (Pas de Calais, 1580) or the Vosges (1682) in France.
We use a numerical modelling method that allows investigating the distribution of deformation caused to by tectonic stresses (i.e., boundary stresses due to the far-field plate motions plus buoyancy stresses due to lateral gradients in gravitational potential energy) and, hence, identifying the intraplate regions where strain may currently be accumulating, with or without observable seismicity. The method is based on the thin-sheet approximation and considers the relative contributions of the lithospheric structure, its rheology, boundary conditions, fault frictions to the predicted velocity and stress fields. We ran a suite of models that we scored against available data on seismic deformation, such as stress directions and GPS velocities. Preliminary results show that the convergence between the Eurasian, Nubian and Adriatic plates results in very little deformation beyond the plate boundary zones, in particular in continental Europe. Models that fit the stress and GPS data best have a "strong" crust and low fault friction (0.01). In such models, predicted long-term slip rates on main faults mapped in central-western Europe are low (often close to 0.01 or 0.001 mm/yr). These models suggest slow extension in the western Alps with strain rates on the order of 6x10-10 yr-1 and compression in foreland. Further work will help disentangle the role of buoyancy versus boundary stresses in driving deformation - and seismicity? - in stable central-western Europe.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.T43D0471T
- Keywords:
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- 3902 Creep and deformation;
- MINERAL PHYSICS;
- 8159 Rheology: crust and lithosphere;
- TECTONOPHYSICS;
- 8160 Rheology: general;
- TECTONOPHYSICS;
- 8164 Stresses: crust and lithosphere;
- TECTONOPHYSICS