Chronology and sediment provenance of extreme floods of Siang River (Tsangpo-Brahmaputra River valley), northeast Himalaya

This study explores paleoflood deposits of the Siang River, known as the Tsangpo in Tibet. The river that often experiences large floods brings down huge amount of sediment and water that adversely affect the downstream regions with large human populations in the states of northeast Himalaya and its foreland. Along it's ~300 km mountainous stretch we collected samples for sedimentological, petrographic and Sr–Nd isotopic study to explore sediment provenance and dated the paleofloods (via optically stimulated luminescence, OSL). Geomorphic indices including precipitation and a geomorphic swath profile across the Brahmaputra catchment were studied to understand the interplay of mountain relief and rainfall that determine potential zones of high erosion and sediment supply. The OSL technique indicated the Siang River experienced at least eight large floods between 7 and 1 ka, possibly under the influence of warm and wet climatic conditions. The petrographic and isotopic data suggests that the eastern Himalayan syntaxis, which has the highest uplift and exhumation rate in the area, is not always the highest sediment producing zone. In some instances, the Tibetan plateau produces higher fluxes of sediments via glacial and landslide lake outburst floods (GLOFs and LLOFs). © 2020 John Wiley & Sons, Ltd.     

Earthquake Genesis and Earthquake Early Warning Systems: Challenges and a Way Forward

Surveys in Geophysics - Several natural hazards, including earthquakes, may trigger disasters and the presence of disaster drivers further lead to the massive loss of life and property, every year...     

Implications of geochemistry in support of Palaeo-Proterozoic tectonothermal evolution of bhopalpatnam Granulite Belt, Bastar Craton, Central India

Bhopalpatnam Granulite Belt which occur along SW margin of Bastar Craton and NE shoulder of Pranhita-Godavari Rift comprise of charnockite (enderbitic variety), garnet-sillimanite-biotite gneiss, quartzo-feldspathic gneiss and corundum bearing aluminous gneiss. High La/Yb ratio, low Eu anomaly (Eu/Eu*=1.0), high LREE/HREE ratio with uniform REE pattern, high La/Sc ratio (0.53–6.43), high Th/Sc ratio (0.03–2.56), low Ni (5.52–20.95), low Cr (31.05–117.05) and uniform Zr/Hf distribution pattern indicate a Proterozoic character. Distribution pattern of K₂O, Na₂O and CaO in ternary diagram show quartz-monzonite-granodiorite trend for the bulk rocks indicating that the bulk rock composition is close to TTG of early Archaean, which might have supplied the sediments for the rocks of Bhopalpatnam Granulite Belt. Geochemical and mineralogical evidence indicate an argillaceous protolith for garnet — sillimanite — biotite gneiss and corundum bearing aluminous gneiss, whereas an arkosic protolith for quartzo-feldspathic gneiss. The geochemical signatures also suggest an active continental margin setting for the rocks of Bhopalpatnam Granulite Belt with prominent Nb and Ta anomaly favouring a subduction environment between Bastar Craton and East Dharwar Craton. This is in conformity with the finding of the earlier workers suggesting a clockwise P-T path based on the combined fluid inclusion and mineral phase equilibria. The LILE geochemistry of charnockite suggests a bi-phase evolution. High LREE/HREE ratio portrays a highly evolved nature of the charnockitic melt generated through partial melting of the continental crust at the final stage of the granulite facies metamorphism during collision between Bastar and East Dharwar Cratons.     

Lava channel of Khedrai Dam,northeast of nasik in western Deccan Volcanic province: Detailed morphology and evidences of channel reactivation

The 120 m-wide Khedrai Dam lava channel is one of the widest recorded in the Deccan Volcanic Province. Like many recent ones, this channel also has a pair of linear marginal levees made of breccia and confines the channelfill lava. It is resting over a pahoehoe flow (substrate) of basalt studded with plagioclase megacrysts, also known as the Giant Plagioclase Basalt (GPB). The channel-fill lava, which makes the lining at the edges and basal portion of the channel, is a comb-layered basalt (Cl-B) characterized by alternating layers rich in curved, branching augite crystals and laths of plagioclase — a texture indicative of high order of supercooling and rapid cooling rates. The dominant and centrally filling lava of this channel is a plagioclase-phyric basalt (Pp-B) that has a wide variation in phenocryst number from megacryst-poor to megacryst-rich. Occurrence of centimetre to decimetre size angular fragments of Cl-B within Pp-B fill indicates mechanical dislodgements of channel-lining by flowing lava. This also suggests that the channel was reactivated before it finally lost its hydraulic gradient and solidified.     

Crustal Heterogeneity and Seismotectonics of the National Capital Region, Delhi, India

To better understand the relationship between crustal heterogeneity and seismotectonics in the National Capital Region (NCR), Delhi, India, we carried out local P- and S-velocity tomography beneath the NCR. First arrival times of the first P- and S-wave from 275 crustal earthquakes recorded by the Seismic Telemetry Network in and around Delhi of the India Meteorological Department, India, are inverted to obtain crustal P-, S-velocity and V _P /V _S variations in the region. Our tomographic images of the upper crust reflect well the surface geological and tectonic features. The Delhi fold belt is identified as low V _P, high V _S and low V _P/V _S. The Sohna hot spring region is appearing as low V _P, low V _S and high V _P /V _S correlating with the possible presence of fluid-filled rocks. The crustal seismicity is distributed in both the high- and low-velocity zones, but most distinctly in the low V _P /V _S region.     

An artificial neural network based approach for urban growth zonation in Dehradun city,India

For regulating urban growth, it is imperative to produce urban growth zonation maps, in which future urbanizable areas along with their urban growth potential are delineated. As, these maps provide a rational and scientific basis for taking future decisions regarding the growth of the city. The conventional approach for generating urban growth zonation maps is subjective in nature. To reduce this subjectivity, an artificial neural network (ANN) approach has been proposed for generating urban growth zonation maps. The database required for ANN-based urban growth zonation has been compiled from remote sensing data and other existing maps. GIS is used for handling of this spatial data. A comparison of the ANN- and conventional approach-derived zonation maps was also done. The study demonstrated the potential of ANN for urban growth zonation of an area, which may provide a valuable input to the urban planning authorities for regulating urban growth     

Earthquake-induced built-up damage identification using IRS-P6 data: a comparative study using fuzzy-based classifiers

The 8 October 2005 earthquake caused widespread destruction in both the state of Jammu and Kashmir of India and Northern Pakistan. Due to poor accessibility in the hazardous and difficult mountainous terrain, a proper and comprehensive ground-based survey was not possible. However, with the help of remote sensing data and its analysis techniques, it is feasible to undertake both earthquake-related damage identification and assessment. This study attempts to document and identify built-up damaged (BD) areas using spectral indices taking temporal multispectral images from IRS-P6 LISS-IV. Five spectral indices have been used to identify BD areas using supervised possibilistic c-means (PCM) and noise cluster (NC) classifiers, to analyse the satellite data. The result indicates that Class Based Sensor Independent (CBSI) based Transformed Normalized Difference Vegetation Index (TNDVI) temporal indices provide the best results for identifying BD areas, while Simple Ratio (SR) index gives the best results for built-up undamaged area identification. Further, it observed that PCM classifier performed better in comparison to NC classifier.     

Multiyear Observations of Deposition-Mode Ice Nucleating Particles at Two High-Altitude Stations in India

Ice nucleating particle(INP) measurements were made at two high-altitude stations in India. Aerosols collected on filter paper at Girawali Observatory, Inter University Center for Astronomy Astrophysics(IGO), and at the Radio Astronomy Center, Ooty(RAC), were activated in deposition mode using a thermal gradient diffusion chamber to determine the INP concentrations. The measurement campaigns at IGO were conducted during 2011, 2013 and 2014, and at RAC during 2013 and 2014. When the aerosol samples were exposed to an ice supersaturation of between 5% and 23% in the temperature range~(-1)7.6?C to-22?C, the maximum INP number concentration at IGO and RAC was 1.0 L~(-1) and 1.6 L~(-1), respectively.A maximum correlation coefficient of 0.76 was observed between the INP number concentration and ice supersaturation. The airmass trajectories analyzed for the measurement campaigns showed that the Arabian Desert and arid regions were the main INP contributors. Elemental analysis of particles showed the presence of Na, Cl, Si, Al, Fe, Cu, Co, Cd, S, Mn and K, as well as some rare-Earth elements like Mo, Ru, La, Ce, V and Zr. When aerosols in the size range 0.5–20 μm were considered, the fraction that acted as INPs was 1 : 10~4 to 1 : 10~6 at IGO, and 1 : 10~3 to 1 : 10~4 at RAC. The higher ratio of INPs to aerosols at RAC than IGO may be attributable to the presence of rare-Earth elements observed in the aerosol samples at RAC, which were absent at IGO.     

Snow cover area variability assessment in the upper part of the Satluj river basin in India

In high-altitude areas, snow cover plays a significant role in mountainous hydrology. Satluj, which is a snow-fed river, is a part of the Indus River system in the western Himalayas. Snow cover area (SCA) variability in this river basin affects the spatio-temporal flow availability and avalanche events. Keeping this in mind, the present study focuses on SCA variability and its relationship with various topographical features such as elevation, slope and aspect. The study has been carried out in the upper part of the Satluj River Basin on the basis of MODIS Terra (MOD10A2) data from 2001 to 2014. It has been noticed that the average annual SCA in this part of the Satluj River Basin varies from 44 to 56% with an average of about 48% of the total basin area of 16, 650 km². Further, snow accumulation and depletion curves have been suggested for assessing the SCA in the study area.     

Crustal Thickness and Composition Variation along the Western Ghats of India through Teleseismic Receiver Function Analysis

Seismic-potential for the Andaman Arc System (AAS) is evaluated using a three-tier approach: (i) the seismic b-values derived using a revised and homogenized earthquake catalog for Mw ≥ 4.7, with uniform Mw, for the period 1964–2013 created from ISC Data, (ii) Free-air gravity-anomalies for AAS and their geologic interpretation and (iii) deep crustal structure from seismic reflection surveys and 3D seismic tomography results. Both long-term spatial b-value anomalies for the period 1964-2013 and temporal b-value anomalies for a shorter period (2002–2013) have been estimated. The b-value maps are interpreted in terms of the stress regime acting across AAS and stressed asperities inferred along the strike of AAS. Eight distinguishable seismic-zones are identified and their seismic potential is examined by temporal bvalue anomalies in producing moderate to large earthquakes. The latter demonstrates ‘low-high’ or ‘high-low’ couplet over years, and that a variation in b-value more than 20% compared to the previous year value is likely to produce an earthquake event with Mw ≥ 6.0. Some support to this interpretation comes from the regional Free-air gravity-anomalies and deep crustal structure interpreted from hypocentral distribution of earthquakes. The high b-values are seemingly associated with magma chambers or low velocity crust; creating asperity zones due to multiple batholithic intrusions at plate boundary. This geologic interpretation is evidenced by 3D P-wave seismic tomography and velocity heterogeneity study for AAS reported by us elsewhere.