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The collision between the Indian and Eurasian plates drives tectonic uplift and evolving landscapes over geological time scales. Much of this evolution is accommodated by seismic processes. However, the relationship between long-term geological processes and short-term seismic cycles is challenging to unravel because of their disparate spatial and temporal scales. Here, we investigate the impact of the internal dynamics of the orogenic wedge on the cycle of Himalayan earthquakes, linking structural models with seismic cycle simulations to show how earthquake patterns may have changed over time. Balanced cross-sections with fault-bend folding at different stages of structural evolution show that frontal thrusts in the Himalayas accumulate slip at different rates across the wedge and over time, depending on the architectural layout of the thrust sheet. Along-strike variations in structural evolution along the Himalayan front may lead to lateral and down-dip segmentation of long-term slip rate, affecting the magnitude and recurrence patterns of earthquakes. Spatio-temporal earthquake patterns may shift every ∼0.3-1.3 Myr as the hanging wall evolves, with implications for seismic hazards in the Nepal Himalayas. 

Abstract The Himalayan megathrust accommodates most of the relative convergence between the Indian and Eurasian plates, producing cycles of blind and surface-breaking ruptures. Elucidating the mechanics of down-dip segmentation of the seismogenic zone is key to better determine seismic hazards in the region. However, the geometry of the Himalayan megathrust and its impact on seismicity remains controversial. Here, we develop seismic cycle simulations tuned to the seismo-geodetic data of the 2015M_w7.8 Gorkha, Nepal earthquake to better constrain the megathrust geometry and its role on the demarcation of partial ruptures. We show that a ramp in the middle of the seismogenic zone is required to explain the termination of the coseismic rupture and the source mechanism of up-dip aftershocks consistently. Alternative models with a wide décollement can only explain the mainshock. Fault structural complexities likely play an important role in modulating the seismic cycle, in particular, the distribution of rupture sizes. Fault bends are capable of both obstructing rupture propagation as well as behave as a source of seismicity and rupture initiation.