In fold‐and‐thrust belts and accretionary prisms, fault bends induce folding in the hanging wall that can alter the long‐term loading rate on the megathrust and profoundly influence earthquake‐related processes. To understand the impact of nonplanar faults and off‐fault deformation on the seismic cycle, we incorporate fault‐bend fold theory into fault dynamics and develop two‐dimensional numerical simulations of slip evolution under a physics‐based rate‐ and state‐dependent friction law. Fault bends can play an important role in earthquake segmentation as a result of nonlinear fault dynamics, affecting the initiation and termination of earthquakes and the details of long‐term interseismic behavior. Shallow earthquakes that initiate, propagate, and terminate near the surface are facilitated when the stratigraphy within incoming thrust sheets is not parallel to the underlying fault, as this can change the loading rate across the fault bend.

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 2015 Mw 7.8 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.

Geodetic networks consisting of high precision and high rate Global Navigation Satellite Systems (GNSS) stations continuously monitor seismically active regions of the world. These networks measure surface displacements and the amount of geodetic strain accumulated in the region and give insight into the seismic potential. SuGar (Sumatra GPS Array) in Sumatra, GEONET (GNSS Earth Observation Network System) in Japan, and PBO (Plate Boundary Observatory) in California are some examples of established networks around the world that are constantly expanding with the addition of new stations to improve the quality of measurements. However, installing new stations to existing networks is tedious and expensive. Therefore, it is important to choose suitable locations for new stations to increase the precision obtained in measuring the geophysical parameters of interest. Here we describe a methodology to design optimal geodetic networks that augment the existing system and use it to investigate seismo‐tectonics at convergent and transform boundaries considering land‐based and seafloor geodesy. The proposed network design optimization would be pivotal to better understand seismic and tsunami hazards around the world. Land‐based and seafloor networks can monitor fault slip around subduction zones with significant resolution, but transform faults are more challenging to monitor due to their near‐vertical geometry.

No abstract