Segmented strain accumulation in the High Himalaya expressed in river channel steepness

We investigate segmentation of High Himalayan strain by cross-orogen structures separating western and eastern obliquely convergent sectors from a central orthogonally convergent sector, and evaluate the relationship between the size of regions accumulating strain, their proximity to the toe of the thrust wedge, and recurrence of M-w > 7 earthquakes. We present a map of river channel steepness (k(sn))-a proxy for rock-uplift rate over 10(5) yr, for the Himalayan arc-and evaluate the strength of its correlation with Main Himalayan thrust (MHT) coupling (-0.6), earthquake density (0.6), topography (0.6), lithotectonic units (0.5), and precipitation (-0.3) along 40 profiles spanning the Himalaya from 78 degrees E to 92 degrees E. We interpret the k(sn) map to be foremost a function of recent strain accumulation. This reveals prominent offsets of hinterland strain accumulation collocated with cross-orogen strike-slip and extensional fault systems. Clusters of high-k(sn) rivers are located near the boundary between the strongly and weakly coupled portions of the MHT, where fault behavior changes from seismogenic to sliding at the rheologic brittle-to-plastic transition (BPT). We propose that the rate at which major MHT earthquakes repeat is related to four parameters: convergence rate (nearly uniform); spatial dimensions of the high-k(sn) cluster (proxy for volume of material accumulating strain); the high k(sn) clusters distance from the toe of thrust wedge (fault surface area over which static friction must be overcome); and the degree of obliquity between India-Asia convergence and the local trend of the orogen (proxy for the magnitude of strain partitioning).