Mechanical analysis of controls on strain partitioning in the Himalayas of central Nepal

Abstract

We present a mechanical analysis of the problem of slip partitioning between the major thrust systems in a collisional range. We focus on two structures in the Himalayas of central Nepal: the Main Himalayan Thrust (MHT) and the Main Central Thrust (MCT). We use finite element modeling to test the influence of various parameters, such as friction coefficients and surface processes, and we investigate how they affect the distribution of deformation between these two faults. We observe that reproduction of the late Quaternary kinematic pattern across the range with our model requires strict conditions on the friction coefficients, such that the MHT is very weak, whereas the MCT is significantly stronger. The most important parameter that controls slip partitioning appears to be the dip angle of the MCT, with a gentler or steeper MCT promoting or inhibiting slip, respectively. We also show that transient loading and unloading through focused glacial erosion in the higher part of the range can unclamp the MCT and allow a significant increase in slip rates. The results of this mechanical sensitivity investigation have important implications for the dynamics of the Himalayan wedge and point toward along-strike structural variations as a first-order control on slip partitioning.