Spatiotemporal variability of neotectonic activity along the Southern Himalayan front: A geomorphic perspective

The interplay of tectonics, climate and erosion has been proposed as the driving factor behind the growth and evolution of the Himalaya. In this review paper, we focus on the neotectonic deformation history within the southernmost morphotectonic sector of the Himalaya (the Sub-Himalaya) through synthesis of geomorphic data. The Sub-Himalaya is arguably consuming ∼100% of the total Himalayan shortening since early Quaternary. We compiled geodetic shortening rates, paleoseismic events (historical earthquakes), shortening rates deduced from uplifted strath/fill terraces and shortening rates from balanced cross-sections from the north-western, central and eastern Himalayan compartments to obtain an orogen-wide perspective of Quaternary deformation. We supported the compiled data with topographic swath, longitudinal river-profile analysis and ks<inf>n</inf> plots of the existing drainage in those compartments. Review of the existing data shows a mismatch of the trend of the geodetic shortening rates with those of the millennial or longer timescales; however, Holocene and modern day-shortening rates are of same range (∼14–21 mm a⁻¹). Quaternary shortening rates are much lower, probably due to a longer time-averaging. Except central Nepal, the other sectors show significant out-of-sequence thrusting (∼50% of the total) within the Sub-Himalaya since the Holocene. Paleoseismic data show variable recurrence intervals of large earthquakes along-strike (∼100–600 years) and large seismic gaps or slip-deficit sectors, which could potentially cause surface-rupture earthquakes in the future.