Transient rivers characterize evolving crustal-scale flexure in the Corinth Rift

Crustal elastic flexure on the flanks of rift-forming faults is a key feature to characterize continental rifting processes that can be resolved by means of transient river drainages on rift footwalls. Here we show that the elastic flexure dynamics of the uplifting southern shoulder of the rapidly-extending, asymmetric Corinth Rift (Greece) are recorded in 3D by its fluvial network. We explore the evolution of the mechanical flexure of the lithosphere at rift full length by means of DEM-based river profile analysis of a series of footwall catchments that drain roughly orthogonal to the rift active fault system. We show that elastic footwall flexure describes the first-order geometry of river longitudinal profiles. Flexure amplitude is maximal in the centre of the rift, where drainage reversal of two catchments suggests very fast slip rates on the active fault system, and decays (i) gently to the west, where transient river profiles exhibit a morphology consistent with relatively lower rates of flexural uplift and there exists evidence for active drainage reorganization, and (ii) sharply to the east, where river profiles are near equilibrium with the modern displacement field. These observations are consistent with landscape responding to growth of a new master fault as a function of slip rate increases and/or onset time. The occurrence of drainage reversal by footwall flexure in the rift centre suggests an extremely rapid footwall flexural uplift due to a sharp increase in master fault slip rate. Lateral changes in river morphology along the rift margin are consistent with either smaller rates of footwall flexural uplift or younger onset of faulting along strike away from the center of the master fault. Further, the extent of flexure, over the full length of the Corinth Rift (~100 km), requires a steep fault growing in a strong crust. These observations are at odds with Corinth Rift growth models of protracted extension and parallel basinwards-migrating faults linked or not at depth with a shallow detachment. To the contrary, our results support the hypothesis of rift growth by lateral along-strike addition of fault segments triggered by a recent shift in plate boundary conditions <1 Ma, an evolution compatible with the southwestwards process zone tip propagation of the North Anatolian Fault.