We review the existing work on one of the principle thrusts, namely, that of Himalayan Frontal Thrust (HFT), caused by the collision between Indian and Asian plates. HFT is the only structure that has observed most of the N-S shortening across the Himalaya. We have carried out an excavation of a 55 m long trench across a scarp (Black Mango Fault) that has displaced the HFT at Kala Amb, Himachal Pradesh. The exposed trench-wall has revealed four low angle thrusts. Analysis of the trench-wall stratigraphy, structure and 14C dating has revealed evidence of two large surface-rupture earthquakes. We have also carried out field study of piedmont zone between Fatehpur and Roorkee. The active deformation observed along the HFT zone suggests increased seismic hazard to the adjoining the Ganga-Yamuna plain. The seismic zonation of India (2001) needs revision in view of geological conditions and past historical seismicity; specifically, we believe that the region between HFT and MBT should be included under zone V category. Multidisciplinary and integrated studies have to be initiated, on a priority basis, covering the central seismic gap region, Uttaranchal
