Active deformation and relief evolution in the western Lurestan region of the Zagros mountain belt: new insights from tectonic geomorphology analysis and finite element modeling

To unravel how and where co-seismic and inter-seismic deformation impacts the spatial and temporal patterns of rock uplift of the Lurestan sector of the Zagros Mountains, we performed an investigation of the large-scale features of topography and river network coupled with 2-D finite element modeling. Geomorphological analysis and constraints from parameters such as elevation, local relief, normalized channel steepness index (ksn), river longitudinal profiles and transformed river profiles (chi-plots), were used to unravel the time–space distribution of vertical motions. Whereas the much longer timescale over which topography grows and/or rivers respond to tectonic or climatic perturbations with respect to even multiple seismic cycles, the outputs of the finite element model yield fundamental information on the source of the late part of the spatiotemporal evolution of surface uplift recorded by the geomorphology. Model outputs shed new light into the processes controlling relief evolution in an actively growing mountain belt underlain by a major blind thrust. The outputs illustrate how co-seismic slip controls localized uplift of a prominent topographic feature – the Mountain Front Flexure – located above the main upper crustal ramp of the principal basement thrust fault of the region, while continuous displacement along the deeper, aseismic portion of the same basement fault controls generalized uplift of the whole crustal block located farther to the NE, in the interior of the orogen.