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Active surface deformation, displacement pattern, and erosional variability is estimated using the geomorphologically sensitive morphometry along with the Persistent Scatterer Interferometric Synthetic Aperture Radar (PSInSAR) technique using the Sentinel-1Adata (119 images) acquired between 07- 02-2017 and 10-02-2021. The average velocities for this dataset are estimated to be between ±11 mm/y. The Raunthi River catchment from where the flood was triggered is undergoing ~8 mm/y subsidence and ~10 mm/y uplift. Compared to this the basin wide deformation (Rishi Ganga basin) is estimated to be around ±10 mm/y with commulative ground displacement of around ±45 mm. The times series analysis suggests an increase in the ground displacement by around 5 mm/y and seems to be responsible for the expansion of pre-existing cracks in the vicinity of the Vaikrita Thrust (VT) and subsequent failure of the northern face of Nandi Peak on 7th February 2021. The Global Positioning System (GPS) derived strain distribution pattern indicate a relatively higher accumulation of strain (>0.35µ strain/y). The normalized steepness index (k sn) variation along the longitudinal section of Rishi Ganga and Raunthi River sub-basin in Central Himalayan region shows anomalous increase at the glacio-fluvial transitional processes. Moreover, the χ profiles as well as planform plots shows anomalously lower values within the Raunthi River sub-basin when compared with the Rishi Ganga basin. Based on the lower values of χ it is observed that Raunthi River sub-basin is undergoing high erosion which can be caused by the presence of sheared lithology and incision of the relict glacial and paraglacial sediments. We negate the suggestion that abrupt rise in the temperature was the major triggering mechanism for the recent disaster, instead it is the sheared lithology and pre-existing fissure developed because of differential uplift and subsidence in Raunthi River that led to the wedge failure and subsequent flash flood. Had the climate was the major driver of the recent tragedy ?, it should have impacted multiple hanging glaciers in the Rishi Ganga valley. Therefore, the study calls for detailed geomorphological, structural and glaciological investigation in regions dominated by glacial and paraglacial processes in the strategic regions of the Himalaya. Towards this, the state of art PSInSAR technique seems to provide fast and reliable detection of terrain instability/stability along with identification of potential areas of slope failures in near future in the glacial and preglacial zones. [ABSTRACT FROM AUTHOR]

The present study area represents one of the active segments of the frontal part of the Arunachal Himalaya. The major structural boundaries traversing the area are the Main Boundary Thrust (MBT) and the Himalayan Frontal Thrust (HFT) and other local faults are tectonically active, as evident from the landforms that evolved in the fault zones. Strath terraces and uplift fluvial terraces are observed in the hanging‐wall block of the HFT and MBT, and along the HFT straight to curvilinear mountain fronts are observed. Normal faults both transverse and parallel to the strike of HFT are observed in the hanging‐wall block of the HFT. West of Pasighat the sub‐Himalaya terrain resembles a duplex, where there is gradual rise in elevation from the Brahmaputra Plain to the low‐lying hills of the sub‐Himalayan and sudden rise in elevation across the MBT. Drainage aligning to the bedrock structures and stream migrations are observed in the fault zones. Along the MBT, the sub‐Himalayan rocks are thrusted over either by quartzite or black carbonaceous shales, in some sections the MBT is behaving as a back‐thrust that dips towards the south. The MBT has also been displaced by almost N–S‐trending transverse faults where highly sheared bedrocks are also observed. Tilting of Quaternary fluvial deposits are observed in the hanging‐wall blocks of intraformational thrusts at two locations. Signatures of paleoseismic activities in the form of various soft‐sediment deformational structures are observed in Quaternary deposits in the HFT zone and also in the hanging‐wall block of the MBT. To determine the deformation and strain rate accumulation, we have re‐analysed the available GNSS results of the area, which indicate a deformation rate of up to 16 mm/year in the vicinity of the Pasighat region. The GPS‐derived deformation rates are well corroborated with the existing results of peak ground acceleration (PGA) anomalies. The component–wise motion indicates higher fault perpendicular motion in this part, which reveals an accumulation of more strain along the major Himalayan faults. [ABSTRACT FROM AUTHOR]

In the northwest Himalayan region, the ongoing out-of-sequence deformation caused emergence of Back Thrust (BT) around 43ka, which attributed the growth of anticlines parallel to the strike of major thrusts. This spatial and temporal geomorphic deformation is accompanied by coexisting river incision in the axial zone of anticlines and base-level fall along with upstream migration of knickpoints in the longitudinal river course. We used the Stream Power Incision model (SPIM) which relates the normalized steepness index (k sn), and concavity index (θ ref) with the slope (S) of longitudinal river profile as a power-law function of upstream area (A). and estimated these parameters for Beas, Soan, and Sutlej rivers to decipher the spatial distribution of deformation pattern. Using SRTM DEM and based on strike parallel variations of the k sn we identified segmented nature of the NW Himalayan thrusts. Further, the dynamics of river basins and transience along the tributaries and main stem rivers has been analyzed by Chi analysis (χ), which is attributed to geometric disequilibrium of the rivers. The results of k sn and χ analysis together suggests that the crustal shortening of NW Himalaya is caused by segmental reactivation of the thrusts. Further, investigating the change in steepness along longitudinal course aids in understanding the differential uplifts patterns in actively deforming segments of major NW Himalayan thrusts. [ABSTRACT FROM AUTHOR]

The consequence of strain accumulation along various Himalayan thrusts is manifested in shaping the topography and present day lanscape features of the Himalaya. Consequently, the strain accomodation is attributed to the occurrence of various devastating earthquakes in the Himalayan domain including 1905 Kangra earthquake (Mw 7.8) which occurred along the Kangra valley fault. In the present study, we analyzed and estimatedsss fault related parameters, gradient-length anomaly (GLA) analysis together with Interferometric Synthetic Aperture Radar (In-SAR) measurements to understand the landscape evolution and deformation pattern within the Soan dun (piggy back basin) in the northwest Himalayan front. We combined the results of geodetic, geological, geomorphology and InSAR to constrain the uplift and subsidence between Himalayan Frontal Thrust (HFT) and Main Boundary Thrust (MBT) zones. The estimated results of fault parameters reveal that the horizontal shortening of northwest Himalaya is higher than the vertical uplift. The computed values of GLA magnitude analysis for the uplifted region vary from −9.21 to −0.77, whereas these range from 5.48 to 26.60 for the subsided region. The depicted range of vertical deformation observed from the InSAR measurements ranges from −3.13 to +3.14 mm/y, where the positive and negative value of phases are correlated with the ground uplift and subsidence. The rate of deformation observed from Persistent Scatterer Interferometry (PSI) phase velocity and GLA magnitude is positively supported by the chronologically constrained uplift rates as 3.4 ± 0.3 mm/y. The geomorphic evidences such as folded, tilted and truncated alluvial fan surfaces, offsetting of channels, fault scarps and displaced sedimentary sequences indicate active nature of the Soan dun. The study would be eventually useful for seismic hazard assessment and future infrastructure development in the seismotectonically active regions like Soan dun of NW Himalayan front. [ABSTRACT FROM AUTHOR]

Geomorphic and morphotectonic evaluations of the Kashmir Basin have been carried by implicating different geomorphic indices such as stream-gradient index (SL), hypsometric integral (HI), drainage basin asymmetry (AF), valley floor height and width ratio (Vf), transverse topographic symmetry factor (T), mountain front sinuosity (Smf), drainage basin shape (BS) and sinuosity index (SI) for the categorization of relative index of active tectonics (RIAT) through the use of geographic information systems (GIS) so as to decipher the role of neotectonics in geomorphologic evolution of the basin. The verified RIAT classes through field investigation and validation reveal the traverse of twenty-one active faults in the basin with demarcation of three RIAT classes viz., class-1 (inactive 20.07% of the area), class-2 (moderately active; 36.52% of the area) and class-3 (very active; 43.4% of the area). The observed values of RIAT distribution pattern are well corroborated with field observations. Ultimately, the overall geomorphic outputs and clustering of recent seismicity support the active tectonic control over the Kashmir basin, India. [ABSTRACT FROM AUTHOR]

Structural and morphotectonic signatures in conjunction with the geomorphic indices are synthesised to trace the role of transverse tectonic features in shaping the landforms developed along the frontal part of the eastern Arunachal sub-Himalaya. Mountain front sinuosity ( S mf ) index values close to one are indicative of the active nature of the mountain front all along the eastern Arunachal Himalaya, which can be directly attributed to the regional uplift along the Himalayan Frontal Thrust (HFT). However, the mountain front is significantly sinusoidal around junctions between HFT/MBT (Main Boundary Thrust) and active transverse faults. The high values of stream length gradient ( SL ) and stream steepness ( K s ) indices together with field evidence of fault scarps, offset of terraces, and deflection of streams are markers of neotectonic uplift along the thrusts and transverse faults. This reactivation of transverse faults has given rise to extensional basins leading to widening of the river courses, providing favourable sites for deposition of recent sediments. Tectonic interactions of these transverse faults with the Himalayan longitudinal thrusts (MBT/HFT) have segmented the mountain front marked with varying sinuosity. The net result is that a variety of tectonic landforms recognized along the mountain front can be tracked to the complex interactions among the transverse and longitudinal tectonic elements. Some distinctive examples are: in the eastern extremity of NE Himalaya across the Dibang River valley, the NW-SE trending mountain front is attenuated by the active Mishmi Thrust that has thrust the Mishmi crystalline complex directly over the alluvium of the Brahmaputra plains. The junction of the folded HFT and Mishmi Thrust shows a zone of brecciated and pulverized rocks along which transverse axial planar fracture cleavages exhibit neotectonic activities in a transverse fault zone coinciding with the Dibang River course. Similarly, the transverse faults cut the mountain front along the Sesseri, Siluk, Siku, Siang, Mingo, Sileng, Dikari, and Simen rivers. At some such junctions, landforms associated with the active right-lateral strike-slip faults are superposed over the earlier landforms formed by transverse normal faults. In addition to linear transverse features, we see evidence that the fold-thrust belt of the frontal part of the Arunachal Himalaya has also been affected by the neotectonically active NW-SE trending major fold known as the Siang antiform that again is aligned transverse to the mountain front. The folding of the HFT and MBT along this antiform has reshaped the landscape developed between its two western and eastern limbs running N-S and NW-SE, respectively. The transverse faults are parallel to the already reported deep-seated transverse seismogenic strike-slip fault. Therefore, a single take home message is that any true manifestation of the neotectonics and seismic hazard assessment in the Himalayan region must take into account the role of transverse tectonics. [ABSTRACT FROM AUTHOR]

In the present study, an attempt has been made to delineate anomalous morphotectonic elements in the lower valley of Ravi and Beas rivers of the NW Himalaya by utilising the digital elevation model (DEM) as well as GIS based approach. We selected the surrounding areas of both the rivers as these have developed tectonically formed lakes such as Khajjiar and Rewalsar in late Holocene and lie in the north and south of Kangra re-entrant structure. We generated topographic swath profiles, calculated normalized steepness index (ksn) and hypsometric integral (HI) and conducted lineament analysis and finally correlated the obtained data set with the contemporaneous seismicity to decode the tectonic activity in the region. Based on the calculated HI for both the areas as 0.45 and 0.47, we infer that there are anomalous changes in the steepness, pointing to the presence of active tectonics. By using lineament analysis, geological information and the quantitative analysis, we identified lineaments parallel and oblique to the regional strike of the NW Himalaya, indicating the area as tectonically active. The lower steepness values along the inferred lineaments suggest the presence of strike-slip features that absorb the oblique convergence of the Indian plate with Eurasia. The GPS based additional observations suggest significant amount of deformation, showing higher deformation rate in the vicinity of the Khajjiar as compared to the Rewalsar locality. Based on remote sensing and GIS based approaches, we conclude that the study area is tectonically very active, hence there is need of careful examination of identified structures and impact on the development of infrastructure and seismic hazard assessment of the western Himalaya. [Display omitted] • Pull apart Sundernagar basin and Rewalsar lake were studied. • KJR exhibits higher steepness than the RWL. • Lithology does not affect steepnessand HI distribution locally. • Lineaments with seismicity supports their tectonic nature. [ABSTRACT FROM AUTHOR]