No abstract

There is increasing evidence that the Himalayan seismicity can be bimodal: blind earthquakes (up to Mw ~ 7.8) tend to cluster in the downdip part of the seismogenic zone, whereas infrequent great earthquakes (Mw 8+) propagate up to the Himalayan frontal thrust. To explore the causes of this bimodal seismicity, we developed a two-dimensional, seismic cycle model of the Nepal Himalaya. Our visco-elasto-plastic simulations reproduce important features of the earthquake cycle, including interseismic strain and a bimodal seismicity pattern. Bimodal seismicity emerges as a result of relatively higher friction and a non-planar geometry of the Main Himalayan Thrust fault. This introduces a region of large strength excess that can only be activated once enough stress is transferred upwards by blind earthquakes. This supports the view that most segments of the Himalaya might produce complete ruptures significantly larger than the 2015 Mw 7.8 Gorkha earthquake, which should be accounted for in future seismic hazard assessments.

A major debate in geophysics is whether earthquakes and slow-slip events (SSEs) arise from similar failure mechanisms. Recent observations from different subduction zones suggest that SSEs follow the same moment-duration scaling as earthquakes, unlike qualitatively different scaling proposed by earlier studies. Here, we examine the scaling properties using dynamic simulations of frictional sliding. The resulting sequences of SSEs match observations from the Cascadia subduction zone, including the earthquake-like cubic moment-duration scaling. In contrast to conventional and widely used assumptions of magnitude-invariant rupture velocities and stress drops, both simulated and natural SSEs have rupture velocities and stress drops that increase with event magnitudes. These findings support the same frictional origin for both earthquakes and SSEs while suggesting a new explanation for the observed SSEs scaling.Plain Language Summary Tectonic faults produce a wide spectrum of slip modes, ranging from fast earthquakes to slow-slip events. Whether slow-slip events and regular earthquakes result from a similar physics is debated. Here we present numerical simulations to show that slow-slip events can result from frictional sliding like seismic slip, with an additional mechanism that prevents acceleration to fast slip due to the presence of fluids. The model succeeds in reproducing a realistic sequence of slow-slip events and provides an excellent match to the observations from the Cascadia subduction zone, including the observation that the moment, which quantifies the energy released by fault slip, is proportional to the cube of the duration. Importantly, our study demonstrates that this scaling arises for different reasons from the traditional explanation proposed for regular earthquakes.

We use a recent compilation of geodetic data of surface displacements in a fully Bayesian approach to derive a probabilistic estimate of interseismic coupling along the Main Himalayan Thrust (MHT). Our probabilistic estimate of interseismic coupling highlights four large, highly coupled patches separated by three potential barriers of low coupling. Locked patches overlap with estimated rupture areas of historical large earthquakes over the past centuries. The coincident spatial variability in coupling, seismicity, and prominent active topography suggests a structural segmentation of the MHT imposed by inherited tectonic structures from the India‐Eurasia collision. This correlation implies that inherited tectonic structures may affect how stress builds up along the MHT, thereby influencing the location and size of large Himalayan earthquakes and the growth of the mountain range.