Holocene shortening along the Himalayan Frontal Thrust in the Nahan Salient, Western Himalaya, India

The Nahan Salient is structurally distinct part from adjacent re-entrants in the northwest Himalaya and has been suggested as structural asperity based on interseismic coupling ratio. The area is located east of the meizoseisimal area of the 1905 Kangra earthquake. In this segment, Himalayan Frontal Thrust (HFT) is exposed at the surface along a river section near Khetpurali village. The displacement along HFT has uplifted the Quaternary fluvial terrace which forms an active fault scarp. The uplifted strath terrace is presently sitting at a height of similar to 34 m from modern river grade. The bedrock incision rates are estimated using OSL ages which yield a value of 4.9 +/- 0.5 mm/yr. Assuming the uplift of the truncated terrace is due to periodic displacements along HFT dipping 30 degrees, during repeated historical earthquakes, the bedrock incision rates equate to fault slip and horizontal shortening rates of 9.8 +/- 1 mm/yr and 8.5 +/- 0.9 mm/yr respectively. The fault is exposed along the Dudhgarh River with Mio-Pliocene Siwalik mudstone-claystone sequences in the hanging wall and Quaternary deposits of Indo-Gangetic plains in the footwall. The fault is capped by a thin continuous strath terrace which has been not deformed by any displacement along HFT. The OSL age of truncated terrace T2 (Sample TK-4) deposits and unfaulted capping unit (T1 Sample TK-2) provide an estimate of the timing of the latest tectonic activity along HFT between 1893 +/- 700 B.C.-1294 +/- 155 A.D. or possibly younger. It implies that no deformation has taken place after deposition of the capping unit i.e., since similar to 1294 A.D. Based on the OSL age of sample TK-2 (0.706 +/- 0.1 ka.), collected from undeformed capping unit across HFT, and using a fault-slip rate of 9.8 mm/year a slip deficit of similar to 6.9 m. has been accumulated since that time in the Nahan Salient.