Electrical imaging of deep crustal features of Kutch, India

A regional Magnetotelluric (MT) study, was carried out with 55 MT soundings, distributed along five traverses, across the Kutch Mainland Unit (KMU), on the west coast of India, a region characterized by a series of successive uplifts and intervening depressions in the form of half graben, bounded by master faults. We obtain the deeper electrical structure of the crust beneath Kutch, from 2-D modelling of MT data along the 5 traverses, in order to evaluate the geo-electrical signatures, if any, of the known primary tectonic structures in this region. The results show that the deeper electrical structure in the Kutch region presents a mosaic of high resistive crustal blocks separated by deep-rooted conductive features. Two such crustal conductive features spatially correlate with the known tectonic features, viz., the Kutch Mainland Fault (KMF), and the Katrol Hill Fault (KHF).
An impressive feature of the geo-electrical sections is an additional, well-defined conductive feature, running between Jakhau and Mundra, located at the southern end of each of the five MT traverses and interpreted to be the electrical signature of yet another hidden fault at the southern margin of the KMU. This new feature is named as Jakhau–Mundra Fault (JMF). It is inferred that the presence of JMF together with the Kathiawar Fault (NKF), further south, located at the northern boundary of the Saurashtra Horst, would enhance the possibility of occurrence of a thick sedimentary column in the Gulf of Kutch. The region between the newly delineated fault (JMF) and the Kathiawar fault (NKF) could thus be significant for Hydrocarbon Exploration.     

Moment Magnitude (M W) and Local Magnitude (M L) Relationship for Earthquakes in Northeast India

An attempt has been made to examine an empirical relationship between moment magnitude (M _W) and local magnitude (M _L) for the earthquakes in the northeast Indian region. Some 364 earthquakes that were recorded during 1950–2009 are used in this study. Focal mechanism solutions of these earthquakes include 189 Harvard-CMT solutions (M _W?≥?4.0) for the period 1976–2009, 61 published solutions and 114 solutions obtained for the local earthquakes (2.0?≤?M _L?≤?5.0) recorded by a 27-station permanent broadband network during 2001–2009 in the region. The M _W–M _L relationships in seven selected zones of the region are determined by linear regression analysis. A significant variation in the M _W–M _L relationship and its zone specific dependence are reported here. It is found that M _W is equivalent to M _L with an average uncertainty of about 0.13 magnitude units. A single relationship is, however, not adequate to scale the entire northeast Indian region because of heterogeneous geologic and geotectonic environments where earthquakes occur due to collisions, subduction and complex intra-plate tectonics.     

Geologic and Tectonic Evolution of the Yinkiong Group and Abor Volcanic Rocks in the Eastern Himalaya: An Overview of Geologic Data

Geotectonics - The Siang valley in the eastern part of Arunachal Himalaya contains Paleocene–Eocene sediments of Yinkiong Group along with the Abor volcanic exposed in a wide lateral extent...     

INFLUENCE OF THE MONSOON TROUGH ON AIR-SEA INTERACTION IN THE HEAD OF THE BAY OF BENGAL DURING THE SOUTHWEST MONSOON OF 1990 (MONSOON TROUGH BOUNDARY LAYER EXPERIMENT-90)

The analysis of 3-hourly time-series data on surface meteorological parameters collected at 20° N, 89° E in the head of the Bay of Bengal during the southwest monsoon period (18 August–19 September) of 1990 under the MONTBLEX-90 programme reveals considerable temporal variability in sea-level pressure, sea-surface temperature (SST) and the fluxes of heat and momentum at the air-sea interface. This variability is related closely to the north-south movement of the monsoon trough and the formation and development of synoptic weather systems during this period. A rapid increase in wind speed, cloudiness, instability, momentum flux, sensible heat flux and moisture flux (by 80 Wm-2), and a decrease of SST (by 0.3 °C) and net surface heat flux by 80 Wm-2, was associated with the development of a depression when the monsoon trough moved southwards. At the peak of the depression, values of the latent heat flux and evaporation reached up to 270 Wm-2 and 1.0 cm day-1 respectively. During the depression period the heat loss across the air-sea interface matched well with the heat loss in the upper (100 m) ocean. With the northward movement of the monsoon trough, the momentum and surface heat fluxes decreased rapidly while the sea surface gained heat energy at rates up to 195 Wm-2.     

Precambrian mafic magmatism of Shillong plateau,Meghalaya and their evolutionary history

The Archaean gneissic basement of Shillong plateau has been traversed by number of mafic dyke swarms. At least two suites of dykes are identified in the region represented by Proterozoic Khasi greenstone related dolerites and younger Cretaceous dolerite dykes in addition to mafic alkaline dykes. The older Khasi greenstone dolerites are altered and have undergone low-grade metamorphism compared to fresh Cretaceous dykes, which are well exposed in the West Garo Hills region. All the Khasi greenstone dolerites are tholeiite in composition and range from basalt to basaltic andesite in composition and show olivine or quartz normative character. Most of the dykes show continental nature of emplacement with some overlapping oceanic tectonic setting of origin. Petrochemical study suggests that they were derived from picrites that subsequently undergone low-pressure fractionation. Palaeomagnetic study of the older Khasi greenstone related dolerites show a direction of magnetization of Dm=17, Im= +57 (α₉₅= 23.34; K=31.5; N=24) with a palaeolatitude of 29.7°N to the Indian subcontinent that clearly support the Proterozoic dyke/dyke swarm emplacement in the region. The magnetic carrier as inferred from K-T studies is in multi domain (MD) size and cation deficient (CD) domain states.     

Early Miocene shell concentration in the mixed carbonate-siliciclastic system of Kutch and their distribution in sequence stratigraphic framework

The Early Miocene succession of Kutch represents a mixed carbonate-siliciclastic depositional system. The carbonate part of the succession, characterized by high abundance of shallow marine benthic fauna, hosts typical shell concentrations (also referred as shell beds). The thickness of shell concentrations vary in scale from 5 cm to 100 cm and are separated by poorly fossiliferous to barren silty shales/siltstones. Based on taphonomic and sedimentological observations, shell concentrations are classified as lag, event, composite/multi-event and hiatal types. The occurrence of different types of shell concentrations in the background of sequence stratigraphic framework is the main theme for the present study. Overall, the shell concentrations occupy the middle part of the sequence i.e. upper part of the transgressive systems tract and lower part of the highstand systems tract. Lag concentrations are found in the lower part of the sequence while composite concentrations, the major contributors in the sequence, occur in upper part of the transgressive systems tract and in the lower part of the highstand systems tract. The hiatal concentrations are associated with maximum flooding surface while the position of event concentrations is independent of sequence stratigraphic framework. The shell concentrations occupy marine flooding surface or marine ravinement surface, thus mark parasequence boundaries.     

Effect of Co‐culture and Nutrients Supplementation on Bioremediation of Crude Petroleum Sludge

Ex‐situ bioremediation of real‐field crude petroleum sludge was evaluated to elucidate the role of co‐culture (bioaugmentation) and external nutrients supplementation (biostimulation) under anaerobic microenvironment. Maximum removal of total petroleum hydrocarbons (TPH) was observed by integrating biostimulation with bioaugmentation (R5, 44.01%) followed by bioaugmentation alone (R4, 34.47%), co‐substrate supplemented operations [R6, 23.36%; R3, 16.5%; R2, 9.88%] and control (R1, 4.36%). Aromatics fraction showed higher degradation in all the conditions studied. Fate of six selected polycyclic aromatic hydrocarbons (PAHs) was evaluated during bioremediation. Among these, four ring PAHs compounds showed good degradation by integration of biostimulation with bioaugmentation (R5) while bioaugmentation alone (R4) documented good degradation of three ring PAHs. Lower ring PAHs compounds showed good degradation with the application of biostimulation (R6). Fluorescent in situ hybridization (FISH) detected the presence of known PAHs degrading microorganisms viz., Bacillus, Pseudomonas, Acido bacteria, Sulphur reducing bacteria Firmicutes, etc. Application of biostimulation and bioaugmentation strategies alone or in combinations documented noticeable influence on the degradation of petroleum sludge.     

Characterisation of groundwater chemistry in an eastern coastal area of Cuddalore district,Tamil Nadu

The groundwater quality detoriation due to various geochemical processes like saline water intrusion, evaporation and interaction of groundwater with brines is a serious problem in coastal environments. Understanding the geochemical evolution is important for sustainable development of water resources. A detailed investigation was carried out to evaluate the geochemical processes regulating groundwater quality in Cuddalore district of Tamilnadu, India. The area is entirely underlined by sedimentary formations, which include sandstone, clay, alluvium, and small patches of laterite soils of tertiary and quaternary age. Groundwater samples were collected from the study area and analyzed for major ions. The electrical conductivity (EC) value ranged from 962 to 11,824 μS/cm, with a mean of 2802 μS/cm. The hydrogeochemical evolution of groundwater in the study area starts from Mg-HCO₃ type to Na-Cl type indicating the cation exchange reaction along with seawater intrusion. The Br/Cl ratio indicates the evaporation source for the ion. The Na/Cl ratios indicate groundwater is probably controlled by water-rock interaction, most likely by derived from the weathering of calcium-magnesium silicates. The plot of (Ca+Mg) versus HCO₃ suggests ions derived from sediment weathering. The plot of Na+K over Cl reflects silicate weathering along with precipitation. Gibbs plot indicates the dominant control of rock weathering. Factor analysis indicates dominance of salt water intrusion, cation-exchange and anthropogenic phenomenon in the study.     

Seismic displacements on shear surfaces in cohesive soils

The paper is concerned with the earthquake-induced displacements on pre-existing shear surfaces in cohesive soils. Results from ring shear tests have shown that during fast shearing the strength of such surfaces depends on displacement and rate of shearing. The test results have been used in a numerical analysis to assess the displacement of a rigid block sliding on a plane surface. The results from the analysis show that the earthquake-induced displacements on pre-existing shear surfaces are influenced significantly by the soil behaviour under earthquake loading conditions. The results are consistent with the field performance of pre-existing slides in cohesive soils during earthquakes.     

Development and evaluation of airborne microwave refractometer for studies on atmospheric tropical boundary layer radiorefractive index

Observations of high-resolution data on radio refractivity were obtained by the airborne microwave refractometer over the Indian sub-continent (a tropical country) from 1971 to 1988. Detailed vertical and horizontal distributions of radio refractivity on a near-real-time basis in the atmospheric boundary layer were determined. Radiosonde observations cannot detect the thin refractivity gradients which characterize the propagation environment in this low-altitude region. This knowledge is required to design reliable and efficient communication systems for strategic, tactical and operational needs. However, the results demonstrate the layer structures and the variability of the boundary layer in time and space. The radio refractive effects on electromagnetic propagation and the future direction of radio refractivity fine-structure measurements are discussed.