Interseismic strain rate and fault coupling along the central Himalayan seismic gap from new GPS data

Abstract

The central Himalayan Seismic Gap (cHSG), which includes the Himachal-Garhwal-Kumaun (HGK) regions of the Indian Himalaya, has been devoid of a great earthquake for more than five centuries. In order to estimate the interseismic strain rate and fault coupling ratio at the Main Himalayan Thrust (MHT) décollement beneath the HGK Himalaya, we analyse 40 new Geodetic Global Positioning System (GPS) data collected between 2003 and 2016 in concomitance with the previous data. The strain analysis distinctly points out the dominant N-S compression along the Himalayan convergent zone. The 2-D elastic dislocation modelling suggests that the entire crustal convergence is accommodated by an average slip rate of 18.5 mm yr-1 over the MHT décollement. Our interseismic coupling model shows that the MHT under the HGK region is strongly and uniformly coupled up to ~100 km from the Main Frontal Thrust (MFT) along the Himalayan arc. The transition from strongly coupled to creeping portions along the MHT occurs within a narrow zone of 40 km. The geodetic moment rate (~3.8 × 1019 Nm yr-1) estimated for the central Himalayan region indicates a large deficit of seismic slip accumulated over the last 500-700 yr and is capable of producing an Mw > 8.7 earthquake.