Comparative evaluation of active tectonics in parts of the frontal region of NW Himalaya, India by geomorphic analysis and geophysical investigation

The Himalayan Frontal Thrust (HFT) is the southern-most boundary of Himalayan mountain belt. It represents a zone of active deformation between the sub-Himalaya and Indo-Gangetic alluvial plain. Morphometric analysis of five sixth order drainage basins along the HFT has been carried out for evaluating relative tectonic activity of the region. Based on the combination of various geomorphic indices such as drainage basin spatial asymmetry, drainage gradient, drainage cross profile and mountain front sinuosity indices, the relative tectonic activity in and around the test site drainage basins was evaluated. Where all the indices are not in agreement, the relative importance of the geomorphic indices was considered to evaluate relative tectonic activity which was then compared with the abundance of drainage anomalies and previously reported active tectonic features (including active faults and fractures). Finally, the results were corroborated with the spatial frequency distribution pattern of previous seismicity (> 2.5 Mw). Geophysical investigation by multi-frequency, bi-static ground penetrating radar (GPR), conducted at selective locations in the piedmont-alluvial region of Solani and Markanda drainage basins, supports active deformation of sub-surface sediment layers. Well-defined offset and warping of near-surface sediment layers indicating the presence of active fault and deformation of sediment layers were observed in 40 MHz and 100 MHz radargrams near Biharigarh and Mujahidpur villages in Solani drainage basin (Uttarakhand and U.P.) and near Toka village in Markanda drainage basin (H.P.).