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Phartiyal B.,University of Lucknow | Singh R.,University of Lucknow | Kothyari G.C.,Institute of Seismological Research
Palaeogeography, Palaeoclimatology, Palaeoecology | Year: 2015

Records from the Tangtse Valley in the Trans-Himalaya reveal depositional history since 48ka, with fluvial aggradation followed by incision, lacustrine sediment fill, and later incision. Varied sedimentary architecture with fluvial episodes intervened by lacustrine pulses, flood events, colluvial and glacial activity are preserved. The valley is located west of the Pangong Tso/Bangong Co, one of the largest lakes in Tibet which has served as a spillway, flooding and damming the entire Tangtse Valley, resulting in the formation of a lake. Today Pangong Tso consists of five basins separated by shallow sills and is fed by snow melt. Documentation based on 14C and OSL chronologies of the sediment sections throughout the valley reveals evidence of a sixth basin of Pangong Tso toward west, occupying the present day Tangtse Valley between 9.6-5.1ka. This event coincides with periods of high lake levels in Tibet, China as well as intensified monsoon periods over the Indian subcontinent. A fluvial regime around 48ka and 30-21ka with comparatively arid conditions and dry phases interspersed by flooding is documented. The valley has been incised to depths of 40-50m in the upper part and to 130m in the lower part. The incision rate ranges from 0.3 to 1.2mmyr-1 in the upper part and reaches as high as 10.8mmyr-1 in the lower valley. Much of the incision took place between 22 and 9.6ka although repeated sediment fill-incision cycles in the valley from 30-22ka, 22-9.6ka, 9.6-5.1ka, 5.1ka, and even to present time were observed. © 2014 Elsevier B.V. Source

Manglik A.,CSIR - Central Electrochemical Research Institute | Pavan Kumar G.,CSIR - Central Electrochemical Research Institute | Pavan Kumar G.,Institute of Seismological Research | Thiagarajan S.,CSIR - Central Electrochemical Research Institute
Tectonophysics | Year: 2013

The tectonics of seismically active Sikkim Himalaya, as inferred by numerous seismological studies, is distinct from the conventional thrust tectonics proposed for the Himalayan collision belt. Here, focal mechanisms of several moderate magnitude earthquakes and composite fault plane solutions of microearthquakes have revealed strike-slip motion along faults transverse to the northward convergence direction of the Indian plate. In the present study, we analyze broadband magnetotelluric data of 12 sites located along an approximately N-S profile cutting across major geological sub-domains of Sikkim to test whether magnetotelluric strikes also support such transverse tectonic nature of the region. We have performed strike analysis of the data by two decomposition approaches as well as by phase tensor method. The study has revealed local variations in the strike directions within the region consistent with the geological and tectonic setup and the presence of transverse tectonic features in the region of Main Central Thrust Zone (MCTZ) where major axis of phase ellipses align in NNW-SSE to NW-SE direction. This trend coincides with the one obtained by microseismic data recorded after the September 18, 2011 earthquake (Mw 6.9). Magnetotelluric strike analysis thus supports the presence of NNW-to-NW trending transverse tectonic zone in MCTZ. © 2013 Elsevier B.V. Source

Kothyari G.C.,Institute of Seismological Research
Zeitschrift fur Geomorphologie | Year: 2015

Morphometric analysis in association with fluvial landform study has been used to ascertain the tectonic instability/stability in Pindar and Saryu River valleys of the central Kumaun Himalaya. To assess tectonic activities in the area, geomorphic indices namely, stream-gradient index (SL), drainage basin asymmetry (AF), topographic asymmetric factor (T), Valley-Floor Height Ratio (Vf) and Elongation Ratio (Re) have been studied. The results of morphometric analysis are in consistent with the field evidences. The study suggests that the terrain close to Main Central Thrust (MCT) and the North Almora Thrust (NAT) is under - going deformation, which is attributed to the regional compression. More specifically, using the valley morphology and longitudinal river profile, the Pindar and Saryu River valleys are divided into three and two broad tectonomorphic zones, respectively. In the Pindar River valley, zone-1 is bounded by the MCT1 to MCT3, Dwali-Phurkiya Fault (DPF), Dulam-Khati Fault (DKF), zone-2 by Askot Thrust (AT) and Baijnath Thrust (BjT) whereas zone-3 is demarcated by Narayanbagar Thrust (NT) and Alaknanda Fault (AF). The two zones in Saryu River valley are bounded by MCT 2 to 3, DKF and AT, NAT. The study suggests that the above-mentioned structures exert significant influence in the evolution of fluvial landform, thus advocates tectonically active nature of the terrain. These structures are considered to be tectonically active. Integrating the morphometry and the geomorphic expressions of tectonic instability suggests that in Pindar River zone-1 and zone-3 are more tectonically active compared to zone-3, whereas in Saryu River valley, zone-2 shows enhanced deformation. © 2014 Gebr. Borntraeger Verlagsbuchhandlung, Stuttgart, Germany. Source

Phartiyal B.,University of Lucknow | Kothyari G.C.,Institute of Seismological Research
Zeitschrift fur Geomorphologie | Year: 2012

The Spiti river basin in North West Indian Himalaya (31-33° E; 77-79 °S), is tectonically unstable, exhibits a complex topography, landscape relief and varied Quaternary sedimentation. The major geomorphic landforms viz., alluvial terraces, strath terraces, alluvial fans, debris cone, fluvio-lacustrine deposits, scree and talus cone are present throughout the valley. An attempt has been made by using the geomorphometry approach to access the area in terms of its neotectonic instability, as this basin feeds the river Sutlej. We tried to see the Spiti and the Parachu basin of draining into Sutlej valley, which have been in news several times in the last decade causing floods downstream, due to the outburst of glacial lakes and the formation of temporary lakes during the sliding events, even by the slight disturbance in the monsoon pattern and tectonic activity. Thus the landforms were mapped and assessed in the valley to elucidate spatio-temporal scale dependencies of surface processes active in this region. The Spiti river (constituting of Spiti and Parachu basins) was examined using geomorphic field methods (Spiti basin) and OSL dating. The Quaternary saw ubiquitous mass movements and catastrophic landslides which transported material from steep slopes to valley bottoms and were responsible for the formation of lakes (preserved as thick sequences of fine sediment), while the outburst floods redistributed sediment downvalley affecting life and property downstream. The morphometric approach such as Basin Asymmetry (AF), Topographic Symmetric Factor (T), Stream length Gradient Index (GI) Hydauralic Sinuosity Index (HSI), Topographic sinuosity Index (TSI) and Standard Sinuosity Index (SSI) have helped in understanding tectonic and climatic perturbation. Our observations point towards a tectonically active region with enormous piles of loose, unconsolidated sediment cover which could be disastrous during the slight shift of the climatic and tectonic forces operating in this area. © 2011 Gebr. Borntraeger Verlagsbuchhandlung Stuttgart Germany. Source

Kothyari G.C.,Institute of Seismological Research | Luirei K.,Wadia Institute of Himalayan Geology
Geomorphology | Year: 2016

The present study has been carried out with special emphasis on the aggradational landforms to explain the spatial and temporal variability in phases of aggradation/incision in response to tectonic activity during the late Quaternary in the Saryu River valley in central Kumaun Himalaya. The valley has preserved cut-and-fill terraces with thick alluvial cover, debris flow terraces, and bedrock strath terraces that provide signatures of tectonic activity and climate. Morphostratigraphy of the terraces reveals that the oldest landforms preserved south of the Main Central Thrust, the fluvial modified debris flow terraces, were developed between 30 and 45 ka. The major phase of valley fill is dated between 14 and 22 ka. The youngest phase of aggradation is dated at early and mid-Holocene (9-3 ka). Following this, several phases of accelerated incision/erosion owing to an increase in uplift rate occurred, as evident from the strath terraces. Seven major phases of bedrock incision/uplift have been estimated during 44 ka (3.34 mm/year), 35 ka (1.84 mm/year), 15 ka (0.91 mm/year), 14 ka (0.83 mm/year), 9 ka (1.75 mm/year), 7 ka (5.38 mm/year), and around 3 ka (4.4 mm/year) from the strath terraces near major thrusts. We postulate that between 9 and 3 ka the terrain witnessed relatively enhanced surface uplift (2-5 mm/year). © 2016 Elsevier B.V. Source

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