Evidence of Strain Accumulation and Coupling Variation in the Himachal Region of NW Himalaya From Short Term Geodetic Measurements

Himachal region of Northwest Himalaya exhibits the widest structural re-entrant in Kangra region and significant strain partitioning along the frontal and hinterland out-of-sequence faults. We report results of continuous GPS measurements from 10 new sites in the region and analyze them along with the previously published results to constrain the ongoing arc-normal and arc-parallel convergence rates at 16.5 +/- 1.1 and 4-5 mm/yr respectively. Thus, the ongoing convergence is oblique by 15 degrees-20 degrees. The Main Himalayan Thrust (MHT) is strongly coupled up to similar to 100 km from the Main Frontal Thrust but displays significant variation in coupling in the transition zone across the Kangra re-entrant and the adjoining western salient. Joint analysis of the coupling variation, the geologically inferred MHT geometry variations and the local topographic anomaly pattern strongly suggest the possibility of a potentially active, strain accumulating segment of MBT along the southern margin of Dhauladhar ranges in Western Himachal region, which is also proposed to be influencing the long-term topographic growth in the region. Although a general agreement is observed between the long-term shortening rates along the active faults and the estimated geodetic convergence in this region, the ensuing discussion highlights their complex relationship in terms of temporal and spatial variability in the fault activity and elastic-inelastic deformation. We use the fault orientation and the estimated convergence rate to geometrically constrain a mean dextral slip-rate of 4.4-5.7 mm/yr along a recently discovered Khetpurali-Taksal fault, which is proposed to partition the majority of ongoing arc-parallel deformation along it.