Abstract
The Himalayan main frontal thrust (MFT) accommodates most of the present-day Indo–Asia convergence with related periodic earthquakes. The seismicity and deformation mechanism varies considerably across the frontal Himalayas. We mapped a segment (Manzai Ranges) of the MFT at the western margin of the Himalayas and analyzed its deformation mechanism and active tectonics using geomorphic indices and the Interferometric Synthetic Aperture Radar (InSAR) Small Baseline Subset (SBAS) technique. Two frontal thrust faults (Khirgi and Jandola) were mapped using Sentinel-2B band ratios in the study area. Water gaps were present in the form of deflected streams at the tip of the growing anticlines. The C-band RADAR interferometry (Sentinel-1A) showed an average uplift of 5–9 mm/year in the satellite line of sight (LOS) from May 2018 to October 2019. The velocity profiles show an uplift variation across the anticlines and may be related to the displacement transfer from the zone of compression in the Manzai Ranges to the zone of transpression in the Pezu–Bhittani Ranges. Four types of morphometric analyses were carried out to assess the relative tectonic activity, namely mountain front sinuosity index (Smf), valley floor width to height ratio (Vf), normalized longitudinal river profile, and normalized channel steepness index (Ksn). The landscape response to active tectonics in the study area was recorded as a deep fluvial incision in V-shaped valleys, convex river profiles, topographic breaks as knickpoints, and a high Ksn index. The geomorphic parameters show a relative increase in tectonic uplift and deformation from the Kundi anticline to the Khirgi and Manzai anticline. We concluded that the frontal structures in the western Himalayas are still going through an active phase of deformation and landscape development with both seismic and aseismic creep.
Highlights
The Indo–Asia collision created the ~2500 km-long seismically active Himalayan mountain belt (55 Ma) [1,2]
The sensitivity of river/stream channels to deformation is a common indicator of active tectonic modification in a Fold–Thrust belt [52]
In a tectonically active region, the drainage pattern is continuously modified in response to changes in the landscape development as a result of fold growth
Summary
The Indo–Asia collision created the ~2500 km-long seismically active Himalayan mountain belt (55 Ma) [1,2]. The main frontal thrust (MFT) marks the southern boundary of this collisional zone (Figure 1). This youngest frontal thrust of the foreland fold and thrust belt of the northwestern. Indian plate lacks a detailed quantitative landscape assessment to categorize the relative tectonic activity. The geodetic data show the movement of the Indian plate at a rate of ~35 mm/year and ~38 mm/year in the northwestern and northeastern margin, respectively [3]. Lave and Avouac [4] proposed that the MFT accommodates most of the present-day Himalayan deformation. The calculated deformation in the northwestern, central and eastern Himalayas are 9 ± 3 mm/year [4,5], 21 ± 1.5 mm/year [6,7], 23.4 ± 6.2 mm/year [8], Remote Sens. 2020, 12, 3362; doi:10.3390/rs12203362 www.mdpi.com/journal/remotesensing which is attributed to an anti-clockwise rotation of the Indian plate [11]
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