Fault reactivation in intraplate domain and driving mechanisms associated to mountain range.

Abstract:

Using thermo-mechanical numeric modelling at lithospheric scale, we test in this study the impact of 3 different processes on the mountain strain pattern and fault reactivation, without convergence. The processes are the following: 1) unloading and loading of the lithosphere 2) isostatic disequilibrium, and 3) thermic anomaly.

Loading and unloading corresponds to sedimentation/erosion and glacial cycles. They generate isostatic rebound inducing elastic upper crust flexural answer and changing stress and strain distribution at regional scale. The generated strain pattern is similar to gravitational collapse with normal faulting in mountain and reverse faulting in the foreland. We test several mountain mean elevations to further understand the mechanism, and then compare it to the data of 21 mountain ranges.

The disequilibrium between Moho and topography induces non-steady state strain and high slip rates difference for fault planes located in and out of the mountain range due to asymmetric, mainly vertical, displacements.

A high temperature anomaly weakens the lithosphere and reduces fault slip rates due to a shallower elastic-viscous transition.

We also pay a specific attention to fault reactivation, for intra-mountain faults, and for far field inherited faults by quantifying and comparing slip rate on pre-defined fault planes in the model. Results show that these 3 processes can produce displacements on faults away from the mountain range area.

Finally we discuss each mechanism influence and compare our results with region that are defined as “stable” with geodetic strain rates below the measurements uncertainties, but with moderate seismicity (M<=5).