Tectonic activity classes along the Nahan Thrust (NT) in NW sub-Himalaya

Morphotectonic analysis using remote sensing images and GIS techniques have been utilized to identify areas experiencing rapid tectonic deformation and to estimate relative variations of tectonic activity along the mountain front in the Morni Hills, marked by the Nahan Thrust (NT) zone. The NT separates the Upper Morni Hills (UMH) from the highly dissected Lower Morni Hills (LMH). The Digital elevation model (DEM) of the area draped with the satellite image was used to identify different geomorphic zones mainly based on altitude and dissection by streams. The NT is also marked by incising streams on the hanging wall block that become braided on the footwall block, across the NT, which can be very well picked on the satellite image. The topographic profiles drawn across the NT, using DEM show a sharp break in slope at the mountain front. Morphometric analysis of the mountain front was carried out determining mountain front sinuosity (S(mf)) derived from remote sensing images and valley floor/valley width ratio (V(f)) indices obtained from topographic profiles using the DEM. The S(mf) values vary from 1.1 to 2.4 that are characteristic of low sinuosity mountain fronts. On the other hand, V(f) values (0.1 to 0.33) are quite low. Both these indices indicate active uplift of the mountain front and consequent downcutting by streams in the hanging wall block. Further, using the S(mf) and V(f) indices, two tectonic activity classes: I (active) and 2 (moderately actively) are identified from the study area.