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Delineation of carbon management zones (CMZs) by capturing geospatial distribution of soil organic carbon (SOC) stock down the profile is an effective strategy for precision agriculture and climate change mitigation. Satellite (Landsat OLI 8), terrain (SRTM 30 m DEM) and bioclimatic (WorldClim dataset) factors were used as covariables in this digital soil mapping approach. Depth harmonization using the quadratic spline method (equal-area) was carried out prior to quantile regression forest (QRF) algorithm-based modelling to estimate SOC stock at six standard soil depths (0-5, 5-15, 15-30, 30-60, 60-100 and 100-200 cm). Soil depth and SOC stock for the whole soil profile were used for the delineation of CMZs using fuzzy k-means clustering. The predicted SOC stock, varied from 14.68 to 42.35 Mg ha-1 in the top layer (0-5 cm depth), while 17.91 to 36.88, 14.15 to 34.70, 12.55 to 35.59, 10.30 to 28.52 and 7.26 to 20.16 Mg ha-1 in the depths of 5-15, 15-30, 30-60, 60-100 and 100-200 cm, respectively. The QRF algorithm performed well in predicting SOC stock with high R2, which ranged from .67 to .83 for all the soil depths. To delineate three CMZs, modified partitioning entropy and the fuzzy performance index were used. In CMZ2, there was a significant increase in SOC stock, followed by CMZ1 and CMZ3. This zone (CMZ2) was located in the central region of the study area and was mostly covered by dense forest and perennial plantations (rubber). The CMZs provided the necessary foundation for the development of site-specific carbon management techniques that can enhance ecosystem service and meet climate change mitigation goals. [ABSTRACT FROM AUTHOR]

Surface wave dispersion data is used to infer the shear wave velocity structure variation in the north‐east Himalaya and Indo‐Burmese arc regions. We have used 25 earthquakes data from four groups with a magnitude range of 5.0–6.7, epicentral distance range 368–800 km, and focal depth less than 50 km. Ray paths from the earthquake location to the seismic station are transversely passing different geotectonic units of the Himalayas, Indo‐Gangetic plains, and Indo‐Burma collision zones. The weighted average dispersion curve and the path averaged shear wave velocity models are computed for the four groups located at different azimuths around Shillong seismic station. Non‐linear least‐square inversion is performed to obtain the shear wave velocity structure of the crust and uppermost mantle from joint inversion of Rayleigh and Love waves group velocities. Subsequently, Rayleigh and Love waves group velocities are inverted separately to obtain vertical and horizontal components of S‐wave velocity. Next, using these components anisotropy coefficient values at different depths for each path are also estimated. A high variation of dispersion curves and the shear wave velocity models from one group to another indicates that the region is geotectonically very complex. An approximately 80 km‐thick zone beneath the study region has shear wave velocity as low as 1.7 km/s in the uppermost crust in the southern part and ~4.7 km in the uppermost mantle beneath the Eastern Himalayan Syntaxis (EHS). Inferred velocity is also lower than that of PREM and AK135 global models with a much thicker crust beneath the study region. Radial anisotropy varies even within the northern part from the Indo‐Eurasian collision zone to EHS and northern to southern Indo‐Burma ranges. Anisotropy is comparatively stronger in the deeper part below ~40 km for the three paths, except for the EHS, where the result is contrary. [ABSTRACT FROM AUTHOR]

Rishi Khola, a sub-watershed of Teesta river, traverses along the Main Central Thrust (MCT) with a multitude of litho units and structural entities. This study examines the impact of tectonic and lithologic controls in configuring the catchment characteristics of Rishi Khola, Sikkim, India. Corrected SRTM 30 m DEM and Landsat 8 satellite image have been used for extracting the river network, preparing the sub-catchments, the longitudinal profile and thereby calculating the morphotectonic indices. An aggregated tectonic index (ATI) has been prepared to map the intensity of tectonic perturbations in the fluvial environment using the entropy weightage method (EWM) and Weighted Linear Combination (WLC). The undulating nature of the longitudinal profile with prominent knick points confirms the presence of tectonic disturbances and lithological variations. From all the computed morphotectonic indices and the ATI, it has been evident that the region has experienced surface deformations. When viewed at the entire catchment, the morphotectonic indices suggest ample responses to the tectonic perturbations due to the dominance of lithology-controlled hill slope processes and fluvial erosion. The spatiality of the tectonic sensitiveness is rather concentrated into certain pockets of differential stress field formed due to fault thrusting of the Himalayas. The study chiefly focuses on the peculiarity of the watershed which displays a complex response of tectonic and rock structure; wherein the proposed methodology has been successful in excavating such complex responses around the Himalayan thrusts. [ABSTRACT FROM AUTHOR]

Landslides are one of the most damaging disastrous phenomena that frequently lead to serious problems in hilly areas. The Namchi region of South Sikkim district as a part of Eastern Himalayas is not an exception to it. In the present study, multi-criteria analysis technique is used for landslide hazard zonation mapping. Various thematic layers, namely slope, rainfall distribution map, lineament density, drainage density, slope aspect, geology, land use/land cover and soil map, were integrated in a GIS platform (ArcGIS 10.1) to delineate landslide hazard zone. Analytic hierarchy process was used to determine the weight values of different factors. Relative rating values are assigned for the subclasses of each thematic layer based on their corresponding impact on the landslide triggers, and within a thematic layer, each class was assigned an ordinal rating from 0 to 9. The landslide hazard zonation map of Namchi region was produced based on weighted overly techniques. The landslide hazard map of Namchi region is divided into five vulnerable zones, namely very low-, low-, moderate-, high- and very high-hazard zones. Resulted landslide hazard zonation map was further validated with field study and geospatial technology-based analysis. The findings demonstrate high-landslide-hazard zones are associated with areas of active erosive processes (steep slopes/cut slopes/lineaments). The results indicate the villages Bomtar, Jorethang, Kopchey, Donok, Namthang, Sumbuk, Longchok, Mamring, Turung, Mikkhola, etc. are highly prone to landslides. The final landslide hazard zonation map can be used for the landslide hazard prevention, proper planning of future infrastructure and geoenvironmental development in Namchi region. [ABSTRACT FROM AUTHOR]

Two contemporary earthquakes originating in the central Himalayan arc and its foredeep (Sikkim earthquake of 18.09.2011, M 6.9, h: 10-60 (?) km and Bihar-Nepal earthquake of 20.08.1988, Mw 6.8, h: 57 km) are commonly associated with transverse lineaments/faults traversing the region. Such lineaments/faults form active seismic blocks defining promontories for the advancing Indian Craton. These actually produce conjugate shear faulting pattern suggestive of pervasive crustal interplay deep inside the mountains. Focal mechanism solutions allow inferring that large part of the current convergence across the central Himalayan arc is accommodated by lateral slip. Similar slip also continues unabated in the densely populated foredeep for distances up to several tens of kilometers south of the Main Boundary Thrust (MBT). [ABSTRACT FROM AUTHOR]

A complete earthquake catalogue of the Western Himalaya (latitudes 30°N–36°N and longitudes 72°E–78°E) for the period of 1501–2010 has been compiled with earthquake magnitude computed in moment magnitude (Mw) scale. Pre- and early twentieth century records of earthquake damage have been documented from rare and out of print publications. Seismotectonics and seismic hazard for Kohistan arc, Kashmir–Hazara Syntaxis, Nanga-Parbat (Western Syntaxis), Karakoram and Himachal Himalaya are discussed with special reference to 1905 Kangra and 2005 Muzaffarabad earthquakes. Analyses of spatio-temporal variation inb-value from the region indicate significant precursor prior to the 2005 Muzaffarabad earthquake; progressive rise of backgroundb-value observed and the main shock locates close to relative highb-value domains. Regions surrounding the location of the 1905 Kangra earthquake also display such highb-value for the period of 2005–2010 that calls for closer scrutiny. Temporal analysis ofb-value from the epicentral block of Muzaffarabad earthquake clearly showed a high–lowb-value couplet of 1.45–0.72, which may be treated as a typical precursor before an imminent large earthquake. Gumbel extreme value statistics indicate probability of occurrence of an event of Mw > 7.0 within 50 years in the region. [ABSTRACT FROM AUTHOR]

We estimate variations of the crustal thickness beneath the Nepal Himalayas based on tomographic inversion of regional earthquake data.We have obtained a low-velocity anomaly in the upper part of the model down to depths of 40 to 80 km and proposed that the lower limit of this anomaly represents variations of the Moho depth. This statement was supported by results of synthetic modeling. The obtained variations of crustal thickness match fairly well with the free-air gravity anomalies: thinner crust patterns correspond to lower gravity values and vice versa. There is also some correlation with magnetic field: higher magnetic values correspond to the major areas of thicker crust. We propose that elevated magnetic values can be associated with more rigid segments of the incoming Indian crust which cause more compression in the thrust zone and lead to stronger crustal thickening. [ABSTRACT FROM AUTHOR]

We estimate variations of the crustal thickness beneath the Nepal Himalayas based on tomographic inversion of regional earthquake data. We have obtained a low-velocity anomaly in the upper part of the model down to depths of 40 to 80 km and proposed that the lower limit of this anomaly represents variations of the Moho depth. This statement was supported by results of synthetic modeling. The obtained variations of crustal thickness match fairly well with the free-air gravity anomalies: thinner crust patterns correspond to lower gravity values and vice versa. There is also some correlation with magnetic field: higher magnetic values correspond to the major areas of thicker crust. We propose that elevated magnetic values can be associated with more rigid segments of the incoming Indian crust which cause more compression in the thrust zone and leads to stronger crustal thickening. [ABSTRACT FROM AUTHOR]

Abstract: The effects of neotectonic activity on geomorphic features have been studied in a large alluvial fan in the foothills area of the eastern Himalayas. The interfluve area between the rivers Mal and Murti is an alluvial fan composed of Quaternary sediments characterized by clay, sand, pebble, and boulder beds. Most of the river valleys in this area show well developed terraces. There are four major terrace surfaces, named as T1, T2, T3 and T4 according to increasing height from the river bed. Two E–W scarps named as Matiali and Chalsa scarps that cut across the fan represent traces of the Main Boundary Thrust (MBT) and the Himalayan Frontal Thrust (HFT) respectively. There are two other NNW–SSE and NNE–SSW lineaments which have partially guided the courses of the Neora and Murti rivers. These are interpreted as conjugate sets of normal faults transverse to the orogenic trend. The E–W scarps are the manifestation of the frontal limbs of the ramp anticlines over two blind thrusts. Fault propagation folding has affected the fan surface. Recurrent movements on the thrusts and consequent downcutting of the rivers have led to the formation of the raised terraces on the banks of these rivers. The terraces are formed by cut-and-fill process. Later transverse normal faulting has given rise to a horst of the Neora–Mal interfluve block. [Copyright &y& Elsevier]

Summary: In river basins where melt water from snow and ice constitutes a dominant component of stream discharge during summer, degradation or reduction of perennial snow and ice covered areas (SCAP ) has a profound effect on stream water availability in those basins. Degradation of SCAP that includes glaciers is a globally widespread phenomenon observed in the recently past decades; its cause has been attributed to global warming and its consequence is expected to dramatically alter the flow regimes of the rivers draining the terrains. The predicted change in flow regime is an initial increase in summer flows in the early decades of 21st century followed by sharp decline of the same during the later parts of the century. Estimation of SCAP within the Upper Indus Basin (UIB), straddling the western ranges of the Greater Himalayas, Karakoram Mountains, and the eastern mountain ranges of the Hindu Kush, shows that from 1992 to 2010 there has been about 2.15% reduction in SCAP . A spatially distributed basin-scale stream water availability model is presented to calculate monthly river discharges at critical hydrologic junctions within UIB. Model calculations for the years 1992, 2000, and 2008, show that due to the degradation of the SCAP within the basin, there has been significant decrease in summer discharges at various hydrologic junctions. The percentage decline in flows varies from 10% to 22%, depending on the locations of the junctions within the basin. The space-dependence of these variations reflects differential degradation of SCAP in various parts of the basin. Furthermore, the time of peak discharge at all of the hydrological junctions has shifted from middle/late summer to late spring/early summer as another outcome of SCAP reduction. Such temporal shifting of nival regimes to early part of warmer season has also been predicted by global warming models. However, the case study presented here for a major Himalayan river basin demonstrates that such shifting of peak discharge in the time domain can also take place simply due to retreat of the equilibrium line. Thus, the effects of a warming climate have possibly been already set within UIB. Instead of experiencing an increased pulse of summer flows for the next few decades, summer flows within this basin are expected to decline. Changes in the timing of peak flows can have adverse effects on multipurpose water resources management without appropriate adaptation and mitigation measures. Monthly average stream flow data with 35year period of record from a key gauging station support the findings of the model results. Similarly, digital maps of SCAP at different time periods within a key catchment of UIB, containing one of the major glaciers, show retreat of glacial lobes and significant decrease in total SCAP taking place during the past decades. [ABSTRACT FROM AUTHOR]

The western Siwalik Himalayas of India experienced the last climate shift 3500 years ago and the soils have been marked by rigorous human activities for a few centuries. An attempt was made to investigate the interactions between soil-forming factors and processes in soil development in relation to land forms and climate change. The hallmark of the soils is the considerable heterogeneity in solum and regolith thickness, horizon boundaries, structural development in surface soils, pH, electrical conductivity and soil mineralogy, irrespective of landscape form and position. A remarkable feature of the soils is the development of deep argillic horizons, or B horizons, in certain landscape positions. The minerals identified were quartz, micas and feldspars in the sand and silt fractions. Illite, kaolinite, vermiculite, smectite and chlorite were present in the clay fractions. Soils under forest vegetation and those recently brought under cultivation belong to Typic Hapludalfs. Soils cultivated over centuries, however, failed to qualify as Alfisols and were classified as Typic/Dystric Eutrudepts. The eroded barren soils were similarly classified as Typic Udorthents. All the soils were low to medium in available nitrogen and phosphorus. The use of nitrogen and phosphorus fertilizer is therefore needed to ameliorate nutrient deficiency and boost crop production. Because of the presence of appreciable amounts of potassium-bearing minerals, soils are likely to be non-responsive to potassium application. The soils of the Dala series (Typic Hapludalfs) are located on moderate hill slopes and thus soil erosion is less severe than for the Mansu series (Typic Udorthent). In the Chamror and Dhar series (Typic/Dystric Eutrudepts) soil erosion is not a serious problem because of terracing and the finer texture of the soils. Crops can thus be grown on profile-stored moisture during dry periods and limited grazing may be permitted. [ABSTRACT FROM AUTHOR]

The Himalayan arc has an arcuate E-W trending geometry with reversal of trend at the terminal ends - Nanga-Parbat (western) syntaxis and Namcha-Barwa (eastern) syntaxis. Both ends are characterized by an actively deformed uplifted dome with its flanks bounded by active shear zones/faults that cause the majority of the seismicity. Compiled map data and seismo-geological depth sections around these two syntaxial zones have brought out active crustal structure and seismotectonic setup. The Nanga-Parbat syntaxis exhibits upward bending and subsequent thickening of the Indian plate with the cluster of seismicity along the NNE-SSW trending Raikhot fault/Diamer shear in its western margin and a comparatively less active Rupal-Chichi shear zone of N-S trend with diffused seismicity towards the east. The 2005 Kashmir earthquake is spawned due to interaction of the Main Boundary thrust and the Muzaffarabad fault. The Namcha-Barwa syntaxis displays a fault-bounded upliftment and thickening of the Indian plate where Canyon thrust marks the boundary between the Indian and Eurasian plates. The occurrence of the 1950 Assam earthquake in the vicinity of the eastern syntaxis is attributed to a regional right lateral strike-slip motion on the causative fault plane. The seismicity in the syntaxes is primarily controlled by strike-slip faults/shear zones along the flanks of popup antiforms. [ABSTRACT FROM AUTHOR]

The Himalayan fold-thrust belt has been visited by many disastrous earthquakes (magnitude > 6) time and again. This active collisional orogen bordering Indian subcontinent in the north remains a potential seismic threat of similar magnitude in the adjoining countries like India, Pakistan, Nepal, Bhutan and China. Though earthquake forecasting is riddled with all conjectures and still not a proven presumption, identifying likely source zones of such disastrous earthquakes would be an important contribution to seismic hazard assessment. In this study, we have worked out spatio-temporal clustering of earthquakes (Mb ≥ 4.5; 1964-2006) in the Himalayas. 'Point density' spatial statistics has helped in detecting 22 spatial seismicity clusters. Earthquake catalog is then treated with a moving time-distance window technique (inter-event time 35 days and distance 100 ± 20 km) to bring out temporal clusters by recognizing several foreshock-main shock-aftershock (FMA) sequences. A total of 53 such temporal sequences identified in the process are confined within the 22 spatial clusters. Though each of these spatio-temporal clusters deserves in-depth analysis, we short-listed only eight such clusters that are dissected by active tectonic discontinuities like MBT/MCT for detail study. Spatio-temporal clusters have been used to constrain the potential source zones. These eight well-defined spatio-temporal clusters demonstrate recurrent moderate to large earthquakes. We assumed that the length of these clusters are indicating the possible maximum rupture lengths and thus empirically estimated the maximum possible magnitudes of eight clusters that can be generated from them (from west to east) as 8.0, 8.3, 8.2, 8.3, 8.2, 8.4, 8.0 and 7.7. Based on comparative study of the eight cluster zones contemplating with their temporal recurrences, historical seismic records, presence of intersecting faults and estimated magnitudes, we have guessed the possibility that Kangra, East Nepal, Garhwal and Kumaun-West Nepal clusters, in decreasing order of earthquake threat, are potential source zones for large earthquakes (≥7.7 M) in future. [ABSTRACT FROM AUTHOR]

According to the most popular tectonic model of the Himalayas proposed by a number of scientists the Indian crustal material underthrusts the Himalayas at a low angle and is relatively free of deformation compared to the overlying accreted material that makes up the Himalayan mountain chain. In this work we have carried out local earthquake tomography for the Garwhal-Kumaun Himalayas to estimate P- and S-wave velocity variations ( Vp and Vs, respectively) and variation in their ratio ( Vp/ Vs) that would indicate the structure of the Himalayas and the underlying Indian crust in this part of the Himalayas. The results indicate that there is crustal level folding and faulting in this region indicating that the underlying Indian crustal material has also undergone deformation unlike what was postulated for the entire Himalayas by some workers before. By comparing our tomographic result with that for the eastern Nepal-southern Tibet region, it is concluded that there is variation in mode of deformation along the trend of the Himalayas. This observation matches well with the observed velocity variation in the upper mantle of these two regions reported by others. The area under investigation falls within a region where there is more oblique convergence between India and Eurasia compared to the Nepal Himalayas region. This may explain why such variation in mode of deformation is observed. The ratio Vp/ Vs gets affected by strength of material. Presence or absence of fluid filled fractures or molten material affects it most strongly in the crustal region. The variation in Vp/ Vs in the study area shows that almost the entire crust here have enough rheological strength such that it can store strain energy that can be released through earthquakes. A zone of low Vp/ Vs beginning at the higher Himalayas and dipping towards SW is observed. This zone also has high Vp and Vs and is observed even when inversion is carried out with very high damping value. These observations do not suggest that seismic hazard will be less in the study area. [ABSTRACT FROM AUTHOR]

Abstract: The relative contribution of intrinsic () and scattering () attenuation to seismic wave attenuation was estimated for the Garwhal–Kumaun Himalayas using Multiple Lapse Time Window Analysis (MLTWA) method under the assumption of isotropic scattering. Local earthquake data recorded by an array operated by Wadia Institute of Himalayan Geology (WIHG), India was used for this purpose. It is observed that scattering attenuation primarily contributes to seismic wave attenuation in this region and its value is much higher compared to that of intrinsic attenuation at around 1Hz frequency. As frequency increases the relative contribution of scattering attenuation to total attenuation starts decreasing. However, as seismic albedo is higher than 0.5 for all the frequencies considered, it is concluded that the medium here is highly heterogeneous in nature. [Copyright &y& Elsevier]

Within the 2500 km stretch of the Himalayas, a narrow window between longitudes 88.185°E and 88.936°E in the frontal Himalayas in North Bengal, crisscrossed by several active fault traces, presents an interesting region for crustal deformation study. We have estimated velocities of 8 GPS stations located in this area and the accumulating strain rate by two different methods. A total shortening of 11.1 ±1.5 mm yr−1 is occurring across a set of four E–W running faults: Gorubathan, Matiali, Chalsa and Baradighi. The strain rate becomes higher in the NE part of the network, reaching −(0.25 ± 0.12) μstrain yr−1 with azimuth 21°. A statistically significant extension of 10.9 ± 1.6 mm yr−1 is estimated across the Gish transverse fault with a maximum strain rate of 0.36 ± 0.08 μstrain yr−1 with azimuth 103°. The accumulating strain will be probably released through future earthquakes. [ABSTRACT FROM AUTHOR]

We analysed local earthquake waveforms recorded on a broad-band seismic network in NW Himalayas to compute the variation of intrinsic and scattering attenuation parameters with depth from coda waves. First we estimated lapse time and frequency dependence of coda Q ( Qc). Intrinsic ( Q−1i) and scattering ( Q−1s) attenuations were separated using Qc and direct S-wave Q ( Qd). It is observed that for smaller lapse time window estimated Q−1c is close to Q−1i and both of them are much larger than Q−1s suggesting that coda decay is predominantly caused by intrinsic attenuation at shallower depth in the NW Himalayas. As lapse time increases, the Q−1c, Q−1i values decrease and come closer to Q−1i values. As Q values for larger lapse time windows are affected by deeper zones, this indicates that with increasing depth relative effect of intrinsic attenuation with respect to that of scattering attenuation on coda attenuation decreases in the area under study. Both coda and intrinsic attenuation decreases with increasing depth. However, between 111 ± 6.3 and 129.5 ± 7.5 km intrinsic attenuation remains stable indicating possible presence of partial melts and/or fluid filled fractures. On the other hand scattering attenuation increases with increasing depth. This may be due to the fact that continental crustal material of the Indian plate underthrusts the Himalayas. The scattering attenuation characteristics of the crust are very different from those of the upper mantle in the NW Himalayas. It is also observed that at higher frequency energy loss is primarily due to intrinsic dissipation, whereas at lower frequency scattering also plays an important role in attenuating seismic wave energy in the study area. [ABSTRACT FROM AUTHOR]

Abstract  We analyzed the local earthquakes waveform recorded on a broadband seismic network in the northwestern Himalayan Region to compute lapse time and frequency dependence of codaQ(Qc). The observedQcvalues increase with increasing lapse time at all frequency bands. The increase inQcvalues with lapse time is attributed to an increase inQcwith depth. This implies that attenuation decreases with increasing depth. The approximate radius of medium contributing to coda generation varies from 55 to 130 km. By comparing theQcvalues with those from other regions of the world, we find that they are similar to those obtained from tectonically active regions. The estimatedQcvalues show a frequency-dependent relationship,Qc=Q0fn, whereQ0isQcat 1 Hz andnrepresents degree of frequency dependence. They represent the level of heterogeneity and tectonic activity in an area. Our results show that northwest Himalayas are highly heterogeneous and tectonically very active.Q0increases from 113  7 to 243  10 andndecreases from 1.01  0.05 to 0.85  0.03 when lapse time increases from 30 to 70 s. As larger time window sees the effect of deeper part of the Earth, it is concluded thatQ0increases andndecreases with increasing depth; i.e., heterogeneity decreases with depth in the study area. [ABSTRACT FROM AUTHOR]

We analysed local earthquake waveforms recorded on a broad-band seismic network in northwestern Himalayas to compute the intrinsic and scattered attenuation parameters from coda waves. Similar to other tectonically active and heterogeneous regions, attenuation-frequency relation for western Himalaya is where is the coda Q parameter. Intrinsic and scattering attenuations was separated using and direct S-wave Q data . It is observed that estimated is close to and both of them are much larger than suggesting that coda decay is predominantly caused by intrinsic attenuation. At higher frequencies, both the attenuation parameters and, are similar indicating that coda is predominantly composed of back-scattered S waves at these frequencies. [ABSTRACT FROM AUTHOR]

Spatial distribution of potassium in mountain soils is governed by landforms, as the operational intensity of factors and processes of soil formation vary with landforms. Therefore, we aimed to find out the relationship between potassium (K) fractions with landforms and the association of K fractions with soil properties. For this, horizon-wise soil samples were collected from pedons, one each from six topographic positions in a catena in the Punjab Himalayas. Samples were analysed for physical and chemical properties and for K fractions. The soils were alkaline and calcareous. The water soluble-K ranged between 4.0 and 18.5 mg kg-1 , exchangeable K between 27.3 and 292.2 mg kg-1, fixed K from 392-240 mg kg-1, and total K from 1.1-3.1%. All forms of K were positively related to silt and negatively to sand. Exchangeable and total forms of K were positively correlated with clay and CEC. The trends could be corroborated with mineralogy, which are rich in K-bearing minerals like micas and feldspars in coarse fractions and illites in clay fractions. The positive coefficients of correlation amongst the forms of K suggest that K forms are present in dynamic equilibria. The spatial distribution of K fractions was closely associated with landforms. [ABSTRACT FROM AUTHOR]

Abstract: The structural evolution of the frontal fold-thrust belt in the NW Himalayas has been deciphered through the construction of a balanced cross section, which incorporates all the Tertiary and the Precambrian sedimentary rock units belonging to the Sub-Himalaya Zone and the Lesser Himalaya Zone, respectively. Towards the foreland the structural geometry is rather simple with widely spaced thrust ramps and simple fault-bend folds in the hangingwall. In the central sector, the structural geometry seen at the surface is essentially controlled by a thrust system that can be approximately described as a buried hinterland-dipping duplex. The structural geometry becomes extremely complex in the northeastern sector (i.e. towards the hinterland) owing to out-of-sequence thrusting, low ramp spacing leading to dislocation of older thrusts and related structures by younger thrusts, folded thrusts, and breached horses. Stacked-up horses, occupied by Lesser Himalaya Zone formations, dominate the structural geometry in this sector. An in-sequence thrusting event followed by out-of-sequence thrusting in an approximately break-back style best describe the structural evolution of the fold-thrust belt in this area. A total slip of about 96km occurred along the detachment and the shortening partitioned within the fold-thrust belt is about 72km or about 71%. [Copyright &y& Elsevier]

The strain rate tensor across the Indian Plate boundary in Himalaya and part of north Burmese arc is calculated from the horizontal velocities of 1252 GPS stations and represented as continuous strain rate map. From the interpolated scalar strain field data, the areas displaying greater than 104 nstrain/yr are marked as 10 seismic source zones. The low b-values (0.53 to 0.73) and related seismo-tectonics indicate compressive nature of these zones. The high strain zones marked in the foothill Himalaya are areas of fault interactions between Himalayan Thrusts of Tertiary age with transverse older Proterozoic reactivated faults (an integral part of basement ridges on under-thrusted rigid Indian plate). Fault interaction is also prominent in EHS area and in Sagaing Fault, where faults from two different tectonic domains are interacting and getting activated by overall clockwise rotational mass movement around plate interface. For calculating seismic vulnerability, we have computed the geodetic moment rates from the measured geodetic strain rates by empirical formula within 15±2 Km seismic volume in these zones, and compared geodetic with seismic moment rate from earthquake catalogue of 100 years. From the moment deficit, the estimated magnitude of earthquake in 10 seismic source zones are calculated which ranges from 6.5 to 7.4. As per our analysis, the Arunachal Himalaya, Sagaing fault, EHS and Himachal Himalaya are posing high seismic threat with occurrence of shallow focus 7.1 Mw earthquake at any point of time [ABSTRACT FROM AUTHOR]

In this study, we obtained new 3D seismic tomography models of the crust and uppermost mantle beneath the northwestern Himalayas down to a depth of 120 km. The data were provided by the India Meteorological Department (IMD) and complemented by the Global International Seismological Centre (ISC) Catalogue. The distribution of anomalies correlates with the main geological features of the region. Specifically, the mountain ranges of the Greater and Lesser Himalaya stand out as a low-velocity anomaly, and the Indian Plate is visible as a high-velocity anomaly underthrusting the Himalayas. The Indian Plate not only underthrusts northwards below the Himalayas, but also bends westwards as it gets closer to the Hindukush Region. A peculiar feature of the model is a high-velocity anomaly in the Kaurik Chango Rift, interpreted as a remnant of the oceanic crust, left after the Indotethys Ocean's closure. In the seismically active Delhi-Haridwar Ridge, a low-velocity upper crustal layer is possibly associated with the sediments of the Indo-Gangetic Plain and with a large number of fault structures. The fragmentation of the Delhi-Haridwar Ridge softens the movement of the Indian Plate to the north, so that the Tethyan Himalaya crust in the area of the Kaurik Chango Fault has remained consolidated and manifests itself as a high-velocity anomaly. The full directory of LOTOS code with data corresponding to this study is available at https://doi.org/10.5281/zenodo.5519210 (accessed on 23 September 2021). • The Indian Plate bends down westwards as it gets closer to the Hindukush Region. • The thickness of the crust varies both across and along the trend of the Himalayas. • The Delhi-Haridwar Ridge softens the movement of the Indian Plate to the north. • There is a remnant of the oceanic crust in the Kaurik Chango Rift. [ABSTRACT FROM AUTHOR]

The attenuation characteristics of the Kinnaur area of the North West Himalayas were studied using local earthquakes that occurred during 2008-2009. Most of the analyzed events are from the vicinity of the Panjal Thrust (PT) and South Tibetan Detachment Thrust, which are well-defined tectonic discontinuities in the Himalayas. The frequency-dependent attenuation of P and S waves was estimated using the extended coda normalization method. Data from 64 local earthquakes recorded at 10 broadband stations were used. The coda normalization of the spectral amplitudes of P and S waves was done at central frequencies of 1.5, 3, 6, 9, and 12 Hz. Q increases from about 58 at 1.5 Hz to 706 at 12 Hz, and Q increases from 105 at 1.5 Hz to 1,207 at 12 Hz. The results show that the quality factors for both P and S waves ( Q and Q) increase as a function of frequency according to the relation Q = Q f, where Q is the corresponding Q value at 1 Hz frequency and ' n' is the frequency relation parameter. We obtained Q = (47 ± 2) f and Q = (86 ± 4) f by fitting power law dependency model for the estimated values of the entire study region. The Q and n values show that the region is seismically very active and the crust is highly heterogeneous. There was no systematic variation of values of Q and Q at different frequencies from one tectonic unit to another. As a consequence, average values of these parameters were obtained for each frequency for the entire region, and these were used for interpretation and for comparison with worldwide data. Q values lie within the range of values observed for some tectonically active regions of the world, whereas Q values were the lowest among the values compared for different parts of the world. Q/ Q values were >1 for the entire range of frequencies studied. All these factors indicate that the crust is highly heterogeneous in the study region. The high Q/ Q values also indicate that the region is partially saturated with fluids. [ABSTRACT FROM AUTHOR]

Abstract: To investigate subsurface structure and seismogenic layers, 3D velocity inversion was carried out in the source zone of 1905 Kangra earthquake (M8.0) in the northwestern Himalaya. P-wave and S-wave phase data of 159 earthquakes recorded by a network of 21 stations were used for this purpose. Inverted velocity tomograms up to a depth range of 18km show significant variations of 14% in Vp and Vs and 6% in the Vp/Vs across the major tectonic zones in the region. Synthesis of seismicity pattern, velocity structure, distinctive focal mechanisms coupled with nature of stress distribution allows mapping of three different source regions that control regional seismotectonics. Accumulating strains are partly consumed by sliding of Chamba Nappe to the southwest through reverse-fault movements along Chamba/Panjal/Main Boundary Thrusts. This coupled with normal-fault type displacements along Chenab Normal Fault in the north account for low magnitude widespread seismicity in upper 8–10km of the crust. At intermediate depths from 8 to 15km, adjusting to residual compressive stresses, the detachment or lower end of the MBT slips to produce thrust dominated seismicity. Nucleation of secondary stresses in local NE–SW oriented structure interacts in complex manner with regional stresses to generate normal type earthquakes below the plane of detachment and therefore three seismic regimes at different depths produce intense seismicity in a block of 30×30km2 centered NE to the epicenter of Kangra earthquake. [Copyright &y& Elsevier]

• Caffeine, an indicator of anthropogenic waste, was associated with estrogenic activity. • Predominance of DnBP at tourist destinations may have plastic litter as its source. • Dominance of BPA in the lower stretch of Ganga is due to industrial effluents. • Only two sites had estrogenic activity that exceeded the pNEC for E2 in fish species. The transboundary River Ganga serves as a conduit for meltwater from the Himalayas and is a major freshwater source for two thirds of Indian population before emptying into the Sundarban Delta, the largest estuary in the Bay of Bengal. Endocrine disrupting compounds (EDCs) such as phthalic acid esters (PAEs) and bisphenol A (BPA) used as organic plastic additives can pollute the aquatic environment receiving plastic litter. Hence, we have investigated these EDCs in water samples from Ganga and Sundarban wetland of India. Since these compounds exhibit estrogenic potential, we have further measured steroids and evaluated the estrogenic activity (estradiol equivalents, Bio E2Eqs) using an in-vitro bioassay (E-Screen). Further Bio E2Eqs were compared with the sum of predicted estradiol equivalents based on the chemical concentrations of PAEs and BPA by E-Screen (Chem E2Eq) and YES factors (Chem YES). Caffeine was measured as a marker for anthropogenic wastewater discharge. Results showed that the highest Bio E2Eq (below the lowest observable effect of E2 on fish) was associated with sites having sewer outfalls in the middle stretch of the river, and concomitantly coinciding with the elevated concentrations of caffeine. Neither ChemE2Eq nor Chem YES correlated with measured Bio E2Eqs. River concentrations of BPA (0.04–4.46 µg/L) and ∑ 7 plasticizers (0.43–7.63 µg/L) were higher than BPA (0.21–2.82 µg/L) and ∑ 7 plasticizers (0.85–2 µg/L) in the Sundarban wetland. The only steroids detected were androgens, found at four sites in Ganga (0.007 µg/L± 0.003, mean ± S.D.). The highest estimated ecotoxicological risk to aquatic insect and fish stemmed from BPA. A secondary effect, and a potential impact on human health could be reflected via fish consumption from the productive fisheries region along the lower stretch of River Ganga. Identification of areas of elevated estrogenicity, plasticizer and steroid concentrations in River Ganga can be used to design and implement interventions for the remediation of such emerging contaminants. Image, graphical abstract [ABSTRACT FROM AUTHOR]

3-D seismic tomography reveals the variations of the crustal thickness beneath the Nepal Himalayas. A low-velocity anomaly in the upper part of the model down to depths of ~40 to 80 km represents crust. Lower limit of this anomaly represents variations of Moho depth. The obtained variations of crustal thickness match fairly well with free-air gravity anomalies: thinner crust patterns correspond to lower gravity values and vice versa. There is also some correlation with magnetic field: higher magnetic values correspond to major areas of thicker crust. We propose that elevated magnetic values can be associated with more rigid segments of the incoming Indian crust which cause more compression in the thrust zone and lead to stronger crustal thickening. Several episodes of collisions and rotation of the Indian plate after collision may also lead to variation in crustal thickness along the tectonic trend of the Himalayas. We have also corroborated estimated seismic velocity structure and crustal thickness with the recent Nepal earthquakes (magnitude ≥7) occurred on April 25, 2015 and May 12, 2015 in the eastern Nepal at the underthrusting interface along the Himalayan arc between the Indian and Eurasian plates. It is found that they occur at/or near the junction of the two anomalous zones of high/low seismic velocities. The patterns of the observed low-velocity anomalies may correspond to the alignments of faults and the high-velocity anomalies may represent the rigid blocks. It is observed that first earthquake of magnitude >7 initiated in a zone where crustal thickness is relatively lower and the rupture propagated eastward towards a region where both crustal thickness and S-wave velocity is higher, i.e. towards a more rigid part of the crust. This may have led to stress loading in the rigid part that subsequently led to occurrence of second magnitude >7 earthquake in that area within a month. The velocity and crustal thickness maps estimated in this study nicely explains why two earthquakes of magnitude >7 occurred within a short span of time within such close distance range. This imply that the first earthquake led to increase in strain in the more rigid body that ruptured when it was strained beyond its elastic limit. Correlation of the velocity and crustal thickness models with the earthquake locations of Nepal that occurred in 2015 solves the enigma why the second earthquake of magnitude > 7 occurred in this region at the eastern end of the rupture zone of the first earthquake. [ABSTRACT FROM AUTHOR]

We investigated Lu–Hf isotopic systematics in garnets from gradually higher grade metamorphic rocks from the first appearance of garnet at c. 500 °C to biotite dehydration melting at c. 800 °C in the Sikkim Himalaya, India. Exceptionally precise Lu–Hf ages obtained for the Barrovian metasedimentary sequence in the Lesser Himalaya (LH) correspond to the time of early garnet formation on a prograde path and show remarkable correlation with increasing metamorphic grade and decreasing structural depth. The youngest age is reported for the garnet zone ( 10.6 ± 0.2 Ma ) and then the ages become progressively older in the staurolite ( 12.8 ± 0.3 Ma ), kyanite ( 13.7 ± 0.2 Ma ) and sillimanite ( 14.6 ± 0.1 Ma ) zones. The oldest age of 16.8 ± 0.1 Ma was recorded at the top of the sequence in the zone marking the onset of muscovite dehydration melting, directly below the Main Central Thrust (MCT). These ages provide a tight constraint on the timing and duration of the Barrovian sequence formation which lasted about 6 Ma. The age pattern is clearly inverted with respect to structural depth but shows “normal” correlation with the metamorphic grade, i.e. earlier garnet growth in higher grade rocks. The timing of the peak metamorphic conditions estimated for the garnet and kyanite zones suggests that thermal climax occurred in all zones within a relatively short time span about 10–13 Ma ago. The metamorphic inversion in the Sikkim Himalaya must therefore have occurred after the metamorphic peak was attained in all grades. Lu–Hf garnet ages in the overthrust Higher Himalaya (HH) continue to be older but do not show a clear progression. There is about 6 Ma jump to 22.6 ± 0.1 Ma within the MCT zone and even older ages of 26–28 Ma were obtained for migmatites from the lower part of the HH. The Lu–Hf system in garnets from the HH records the time of melting at or near the thermal peak rather than dates initial garnet growth as in the LH. The age pattern obtained in this study provides precise time constraints on the continental collision models which must take into account early and prolonged anatexis in the HH, progressive delay in initial garnet growth in different Barrow zones in the LH, nearly contemporaneous metamorphic peak in all grades and post peak inversion of the coherent LH block during exhumation. [ABSTRACT FROM AUTHOR]

The present study discusses the geochemistry of the Early Cretaceous Shyok and Nubra volcanics from the Shyok Suture Zone (SSZ), Trans-Himalaya. Geochemically, the studied volcanic rocks belong to calc-alkaline magma series and vary in composition from basalt-basaltic andesite-andesite-dacite. The SSZ rocks are enriched in light rare earth elements (LREE: La, Ce, Nd) and large ion lithophile elements (LILE: Rb, Ba, U, K, Pb and Sr) while depleted in high field strength elements (HFSE: Nb, P and Ti), analogous to subduction zone magmatism. Their perturbed LILE concentrations coupled with higher 87Sr/86Sr ratios reflect possible influence of post-crystallization processes. Trace element modelling reflects variable degrees of partial melting (~5–30%) of a metasomatised spinel peridotite mantle source followed by fractional crystallization of clinopyroxene and amphibole along with olivine and plagioclase. The Shyok and Nubra volcanics depict positive ε Nd (t = 110 Ma) values (+2.3 to +5.2), slightly lower than the contemporary Chalt fore-arc boninites (+6.3 to +8.0) and adjoining intra-oceanic island arc rocks along the Indus Tsangpo Suture Zone (ITSZ) such as Nidar ophiolite (+6.8 to +8.7), Shergol gabbros (+5.1 to +8.4) and Dras volcanics (+5.8 to +7.0), therefore reflecting depleted mantle characteristics. In contrast to the ITSZ rocks, the Shyok and Nubra volcanics have enriched LREE-LILE characteristics, indicating their derivation from isotopically depleted and elementally (LREE-LILE) enriched mantle wedge sources. Thus, based on the geochemical and isotopic signatures of the SSZ rocks and their association with continentally derived sediments, we suggest an Andean-type arc system as opposed to ITSZ rocks and associated oceanic sediments, representing intra-oceanic arc system. [Display omitted] • The Shyok and Nubra volcanics belong to calc-alkaline magma series. • Variable degrees of partial melting of a metasomatized spinel-peridotite. • Positive εNd(t = 110 Ma) values (+2.3 to +5.2) are analogous to Andean-type arc system. [ABSTRACT FROM AUTHOR]

Foreland basins associated with collisional mountain belts undergo postdepositional deformation in response to compressive stress exerted from the evolving orogen. The low thermal regime of such processes requires sensitive methods to unravel the structural evolution of such regions. In this study, we conducted apatite fission track (AFT) and (U-Th)/He thermochronology on the sedimentary succession of the Subathu basin in the Himalayan foreland of the Himachal Pradesh region in India, an area preserving the sedimentary record of the India-Asia collision since the late Paleocene-early Eocene. The results show that the Subathu basin exposes a fossilised apatite partial annealing zone (APAZ) depicted by incompletely reset AFT ages and shortened track lengths in the Paleocene-middle Miocene pre-Siwalik units and unreset ages in the Neogene Siwalik Group. We associate the partial annealing of the pre-Siwalik rocks with thickening due to internal imbrication and nappe stacking triggered by shearing along the Main Boundary Thrust and its splays since the middle Miocene. Thermal modelling of the Siwalik rocks projects a rapid heating up to approximately 90–100 °C reached between 4 and 1 Ma. Following the thermal peak, the Siwalik rocks cooled rapidly, as indicated by 2.6–1.2 Ma AHe ages. We associate this recent cooling event with SW-directed thrusting along the Main Frontal Thrust, which placed the foreland basin over the Gangetic Plains. Our results are similar to those obtained for the foreland basin in Nepal, indicating that the movement along the youngest major discontinuity of the Himalaya is synchronous along the orogen. • Foreland basin in the NW Himalaya exposes apatite partial annealing zone • Thermal climax achieved during nappe stacking linked to thrusting along the MBT • Rapid cooling of the Siwalik sediments records initiation of the MFT at 1 Ma [ABSTRACT FROM AUTHOR]

Abstract: Geomorphic landscape and late Quaternary geological attributes from the Raidak–Manas interfluve in the Bhutan–Himalayan foothills, Kokrajhar District, Assam led towards documenting the east–west trending, south dipping, 30km long active Frontal Back Thrust (FBT), well within the foredeep south of the Main Frontal Thrust (MFT). Spectacular north facing 6–50m high tectonic-scarp generated by the north-propagating emerging thrust front along with a complementary subdued south-facing scarp defines the terrain as a pop-up structure. The entire belt is made up of 5 to 8km wide six distinct blocks, separated by antecedent rivers/streams. Scarp parallel east–west drainage along with linear lakes characterises the emerging thrust front. Field evidence for a major fault-propagation fold structure along with thrust faulting within the late-Quaternary fluvial sediments is ubiquitous. Clay beds deposited in lakes along the footwall of FBT have formed due to blockade of south flowing rivers by episodic upliftment of the hanging wall block; three such episodes of uplift since 16k years correspond to three morphogenic earthquakes of magnitude ~6.9 rupturing the FBT during late Pleistocene–Holocene. In light of geomorphological and geological studies, neotectonic activity has been modelled as an active south dipping backthrust that originates at shallow crustal depth from south vergent basal Himalayan Decollement in response to the advancing Himalayan wedge. [Copyright &y& Elsevier]