Transient deformation and long-term shear zone activity

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During orogeny on the time scale of Millions of years, crustal blocks are offset over kilometre-scale distances along shear zones. Transient deformation at high and then relaxing stresses in shear zones can be triggered by seismic slip events taking place on the time scale of seconds. - What is the signature of multiple seismic events in the geological record from the base of the seismogenic zone? - How can different transient high-stress deformation events in a specific rock be distinguished? - What is the role of transient deformation on the long-term shear zone activity?To address these questions we propose a field-based and micro-analytical approach on the base of the Silvretta nappe in the Central Alps. There, mutually crosscutting mylonites and pseudotachylytes are well exposed. We will analyse the deformation history that is recorded by these crosscutting relations considering deformation in dependence to the tip of a propagating seismic active fault. We will test whether they indicate (1) a specific sequence of accelerated creep followed by deformation at transiently high and then relaxing stresses, or (2) a cyclic overprinting of several high-stress deformation events. We aim at a conceptual model for the temporal and spatial scale–dependent rheology related to the distance to the tip of a propagating seismic active fault. The findings will be discussed in the light of the specific characteristics in thrust regimes and compared to those of different tectonic regimes. The findings are expected to lead to a better understanding on the role of seismic slip and related deformation at the base of the seismogenic zone on the long-term shear zone activity offsetting crustal blocks over kilometre-scale distances.