• Volume 124, Issue 3

April 2015,   pages  487-680

• Accuracy of Cartosat-1 DEM and its derived attribute at multiple scale representation

Digital Elevation Model (DEM) provides basic information about terrain relief and is used for morphological characterisation, hydrological modelling and infrastructural studies. This paper investigates the accuracy of DEM and its derived attributes in multiple scales. This study was carried out for a part of Shiwalik Himalaya using Cartosat-1 stereo pair data. DEM at various cell sizes were generated and information content was compared using mean elevation, variance and entropy statistics. Various post-spacing DEMs were validated to understand variation in vertical accuracy along different scales. The vertical accuracy (3.14–7.24 m) is affected in larger spacing DEM and elevation is underestimated. Slope of terrain also has similar impacts. The DEM and slope accuracy are also affected by the terrain roughness while assessing coarser grid size.

• Latitudinal variation in the occurrence of GPS L-band scintillations associated with the day-to-day changes in TEC, h′F and the E×B drift velocity and their impact on GPS satellite signals

The present study describes the day-to-day variations in the occurrence of GPS L-band scintillations from equator to the anomaly crest location associated with the changes in TEC, h′F and E×B drift velocities. The GPS–TEC and S4 index data from an equatorial station, Trivandrum (8.47°N, 76.91°E), a low latitude station, Waltair (17.7°N, 83.3°E) and an anomaly crest location Kolkata (22.6°N, 88.4°E) during the low solar activity years of 2004 and 2005 are used. It is observed that the day-time ambient TEC is higher during scintillation days compared to that during the days on which there are no scintillations at the three different locations mentioned above. Further, the diurnal variation of TEC shows a rapid decay during 1700–2000 hr LT over the three different locations during scintillation days which is observed to be comparatively much less during no scintillation days. The average height of the F-layer in the post-sunset hours over Trivandrum is found to be higher, around 350 km during scintillation days while it is around 260 km during the days on which there is no scintillation activity. The average pre-reversal E×B drift velocity observed around 19:00 hr LT is higher (20 m/s) during scintillation days, whereas during no scintillation days, it is found to be much less (7 m/s). Further, it is observed that the GPS receivers lose their locks whenever the S4 index exceeds 0.5 (&gt;10 dB power level) and these loss of lock events are observed to be more around the anomaly crest location (Kolkata). It may be inferred from the present observations that the level of ambient ionization around noon-time, and a fast decay (collapse) of the ionization during afternoon hours followed by rapid increase in the height of the F-layer contributes significantly to the occurrence of scintillations. The present study further indicates that the S4 index at L-band frequencies increases with an increase in latitude maximizing around the crest of the equatorial ionization anomaly during the post-sunset hours resulting in more loss of lock events in the GPS receiver signals around the EIA crest region.

• Cyclone hazard proneness of districts of India

Hazards associated with tropical cyclones (TCs) are long-duration rotatory high velocity winds, very heavy rain, and storm tide. India has a coastline of about 7516 km of which 5400 km is along the mainland. The entire coast is affected by cyclones with varying frequency and intensity. Thus classification of TC hazard proneness of the coastal districts is very essential for planning and preparedness aspects of management of TCs. So, an attempt has been made to classify TC hazard proneness of districts by adopting a hazard criteria based on frequency and intensity of cyclone, wind strength, probable maximum precipitation, and probable maximum storm surge. Ninety-six districts including 72 districts touching the coast and 24 districts not touching the coast, but lying within 100 km from the coast have been classified based on their proneness. Out of 96 districts, 12 are very highly prone, 41 are highly prone, 30 are moderately prone, and the remaining 13 districts are less prone. This classification of coastal districts based on hazard may be considered for all the required purposes including coastal zone management and planning. However, the vulnerability of the place has not been taken into consideration. Therefore, composite cyclone risk of a district, which is the product of hazard and vulnerability, needs to be assessed separately through a detailed study.

• Aquifers productivity in the Pan-African context

In this study, 50 Vertical Electrical Soundings (VES) were carried out in the region, including 14 near existing boreholes for comparison. Aquifer parameters of hydraulic conductivity and transmissivity were obtained by analyzing pumping test data from existing boreholes. An empirical relationship between hydraulic conductivity (K) obtained from pumping test and both resistivity and thickness of the Pan-African aquifer has been established for these boreholes in order to calculate the geophysical hydraulic conductivity. The geoelectrical interpretation shows that almost all aquifers are made of the fractured portion of the granitic bedrock located at a depth ranging between 7 and 84 m. The hydraulic conductivity varies between 0.012 and 1.677 m/day, the resistivity between 3 and 825 𝛺m, the thickness between 1 and 101 m, the transmissivity between 0.46 and 46.02 m2/day, the product K𝜎 between 2.1 × 10−4 and 4.2 × 10−4.

• Assessment of the regional water balance of the limestone subaquifers of Cyprus

The northern part of Cyprus is usually characterized by its small watersheds and the lack of ephemeral surface water resources. Therefore, all the water dependent activities depend on groundwater resources. Kyrenia Range subaquifers are the only natural domestic water supplying sources, fulfilling the required worldwide drinking water quality standards. In the present study, various hydrogeological factors that could influence the aquifer recharge and abstraction are used together with annual groundwater level changes, to estimate the capacity of each subaquifer distributed at the Kyrenia Range randomly. During the analyses, 11 subaquifers are worked out; and their spatial distribution, the depth, and the daily abstraction from the available wells are surveyed. The results show that annual groundwater recharge into the subaquifers is 1126 mm. It is also observed that the subaquifers recharging from the southern foothills are more vulnerable to climate effects than the ones at the northern foothills. The available water storage at the present situation, at each subaquifer, is calculated individually and finally the total storage capacity of Kyrenia Range subaquifers, is assessed as 214 million cubic meters (MCM); whereas the data analyses show that annual abstractions from the 11 subaquifers is 13.34 MCM, annually.

• Observed linear trend in few surface weather elements over the Northwest Himalayas (NWH) during winter season

Linear trends in few surface weather variables such as air temperatures (maximum temperature, minimum temperature), snow and rainy days, snowfall and rainfall amounts, rainfall contribution to seasonal total precipitation amount, seasonal snow cover depth and snow cover days (duration) are examined from winter-time observations at 11 stations located over the Northwest Himalayas (NWH). This study indicates that snowfall tends to show a decline in this region, while the rainfall tends to increase during the winter months. Seasonal snow cover depth and seasonal snow cover days also tend to show a decline over the NWH. Decrease in seasonal snow cover depth and duration have reduced the winter period in terms of availability of seasonal snow cover over the NWH during the last 2–3 decades. Other surface weather variables also exhibited significant temporal changes in recent decades. Observed trends in temperature and precipitation over the NWH in recent decades are also supported by long data series of temperature over the western Himalayas (WH), north mountain India (NMI) rainfall data and reanalysis products.

• Evolution and outburst risk analysis of moraine-dammed lakes in the central Chinese Himalaya

The recent evolution and outburst risk of two typical moraine-dammed lakes, Galong and Gangxi, central Chinese Himalaya, are analyzed using topographic maps from 1974 and Landsat satellite imagery acquired in 1988, 2000 and 2014. The datasets show the areas of Galong and Gangxi lakes increasing at rates of 0.45 and 0.34 km2/year during the period 1974–2014, an expansion of 501% and 107%, respectively, in the past 41 years, while the areas of the parent glaciers, Reqiang and Jipucong decreased by 44.22% and 37.76%, respectively. The accelerating retreat of the glaciers not only reflects their generally negative mass balance but is consistent with the rapid expansion of the moraine-dammed lakes. When acted upon by external forces such as earthquakes, heavy rainfall, rapid melting of glaciers and dead ice, and snow/ice/rock avalanches, these lakes can become extremely dangerous, easily forming outburst mudslides, which can potentially spread to the Poiqu river basin and develop into cross-border (China and Nepal) GLOF disasters. Therefore, there is an urgent need to strengthen integrated risk management of glacial lake outburst disasters with multiple objectives and modes.

• Probabilistic seismic hazard assessment of NW and central Himalayas and the adjoining region

The Himalayan region has undergone significant development and to ensure safe and secure progress in such a seismically vulnerable region there is a need for hazard assessment. For seismic hazard assessment, it is important to assess the quality, consistency, and homogeneity of the seismicity data collected from different sources. In the present study, an improved magnitude conversion technique has been used to convert different magnitude scales to moment magnitude scale. The study area and its adjoining region have been divided into 22 seismogenic zones based upon the geology, tectonics, and seismicity including source mechanism relevant to the region. Region specific attenuation equations have been used for seismic hazard assessment. Standard procedure for PSHA has been adopted for this study and peak ground motion is estimated for 10% and 2% probability of exceedance in 50 years at the bed rock level. For the 10% and 2% probability of exceedance in 50 years, the PGA values vary from 0.06 to 0.36 g and 0.11 to 0.65 g, respectively considering varying 𝑏-value. Higher PGA values are observed in the southeast part region situated around Kaurik Fault System (KFS) and western parts of Nepal.

• Morphotectonic analysis, structural evolution/pattern of a contractional ridge: Giouchtas Mt., Central Crete, Greece

The Giouchtas Mountain is situated south of Heraklion, Central Crete. It is a N–S trending morphological asymmetric ridge with a steep western slope, whilst its eastern slope is characterized by a smoother relief, composed of Mesozoic limestone and Eocene–lower Oligocene flysch of the Gavrovo–Tripolis zone. The present study focusses on the structural pattern and development of Giouchtas Mountain. Morphotectonic analyses in combination with field mapping and tectonic analysis were performed for this purpose. GIS techniques were used for mapping the spatial distribution of the geological features on the topographic relief of the area. Geomorphic indices, used in the present study, are the mountain front sinuosity index (Smf) and the valley floor/width ratio index (Vf). Based on Smf and Vf values, it is implied that this area can be assigned to a tectonic class I, corresponding to higher tectonic activity. However, spatial variations of the tectonic activity along the segmented fronts point to a general trend of increasing activity towards the north and especially, northeast. The model of this possibly active structural feature corresponds to a compressional mechanism followed by an earliest Mid. Miocene to Holocene late-stage deformation related to extensional faulting.

• A study on variation in position of an Indian station due to solid earth tides

In many geodetic analyses, it is important to consider the effect of earth tide on the instantaneous position of a station and its subsequent influence on the computation and interpretation of time series of coordinates as well as related data products. The tidal effect and temporal variations in the position of the IGS (International Global Navigational Satellite Systems [GNSS] Service) stations at Hyderabad (India), Ankara (Turkey) and Beijing Fangshan (China), due to solid earth tides has been studied. Surface tidal displacement of the station has been computed on daily basis for a month, based on the concept of gravity. Further, mean daily coordinates of the station been computed using static precise point positioning (PPP) method for a month. Results show that the station undergoes temporal displacements and its coordinates vary continuously within a day and all the days in the month. The maximum range in vertical displacement of the station has been found to be about 48 cm in a day over a period of a month and that along the north and east directions is respectively 8 cm and 14 cm. This is the maximum range but the mean value in the vertical displacement is 6 cm and along north and east is 1.7 cm and 0.09 cm, respectively. The ranges in variation in the mean value of geodetic latitude, longitude, and height of the station have been found to be 1.23, 2.73, and 3.52 cm, respectively. Further, it has been found that the tidal oscillations follow some periodicity, and thus need to be studied independently for all stations.

• A relook into the crustal architecture of Laxmi Ridge, northeastern Arabian Sea from geopotential data

In this study, we undertake analysis of ship-borne gravity-magnetic and satellite-derived free-air gravity (FAG) data to derive the crustal structure of Laxmi Ridge and adjacent areas. 2D and 3D crustal modelling suggests that the high resolution FAG low associated with the ridge is due to underplating and that it is of continental nature. From Energy Spectral Analysis, five-depth horizons representing interface between different layers are demarcated that match those derived from 2D models. Magnetic sources from EMAG2 data, various filtered maps and absence of underplating in the EW section suggest that the EW and NW–SE segment of the Laxmi Ridge is divided by the Girnar fracture zone and probably associated with different stages of evolution. From the derived inclination parameters, we infer that the region to the north of Laxmi Ridge, between Laxmi and Gop Basins, is composed of volcanic/basaltic flows having Deccan affinity, which might have been emplaced in an already existing crust. The calculated inclination parameters derived from the best fit 2D model suggests that the rifting in the Gop Basin preceded the emplacement of the volcanics in the region between Laxmi and Gop Basins. The emplacement of volcanic/basaltic flows may be associated with the passage of India over the Reunion hotspot.

• Late Cretaceous evolution of the northern Sistan suture zone, eastern Iran: Implications of magnetic fabrics and microstructures in the Bibi Maryam granitoid

Anisotropy of magnetic susceptibility (AMS) survey supported by field and microstructural studies have been applied on the Late Cretaceous Bibi Maryam granitoid (BMG) in the northern Sistan suture zone (SSZ), east of Iran. The BMG is composed of quartzdiorite-tonalite with late granodiorite dykes and stocks that are surrounded by steeply SW-dipping Neh shear zone (NSZ). The magmatic fabrics are characterized by transpressional environment dominated by steep dipping foliations (mean strike: N13°W) and sub-horizontal stretching lineations (mean trend: 167°). Based on microstructural studies, it is inferred that these fabrics are related to emplacement and cooling of the pluton and the internal fabrics revealed are evidence of a deformation continuum in the granitoid from magmatic to solid state. Deformation in the region continued even after the BMG had fully crystallized, which led to development of the NW–SE foliations and lineation trend that these fabrics are subparallel with the NSZ. The BMG has emplaced in a transpressional setting that was controlled by a NW–SE stretching direction and supported the model that has proposed the relationship between granitoid emplacement and oblique intra-oceanic subduction of the Neotethys during the Late Cretaceous already recognized in this part of the SSZ.

• Origin of banded structure and coal lithotype cycles in Kargali coal seam of East Bokaro sub-basin, Jharkhand, India: Environmental implications

The Kargali seam of Early Permian Barakar cyclothems of East Bokaro sub-basin of Jharkhand, India is 12–30 m thick, splits into two parts, and extends throughout the length of the basin. It is made up of interbedded sequences and variable proportions of Vitrain, Clarain, Durain and Fusain. Application of embedded Markov chain model rejects the phenomenon of randomness in the repetition of coal lithotypes. The preferential upward transition path for coal lithotypes that can be derived for the Kargali top coal seam is: Vitrain $\to$ Clarain $\to$ Durain $\leftrightarrow$ Fusain $\to$ Vitrain, and for the Kargali bottom coal seam is: Clarain $\leftrightarrow$ Vitrain $\to$ Fusain $\to$ Durain $\to$ Clarain. By and large, the cyclic repetition of coal lithotypes is similar in the Kargali bottom and top seams. Among the noteworthy features are two-way transitions between Durain and Fusian in Kargali top and between Clarain and Vitrain in the case of Kargali bottom coal seam. Entropy analysis corroborates Markov chain and indicates the presence of type A-4 asymmetrical cycles of coal lithotypes.

It is suggested that the banded structure of a coal seam is not a random feature and follows a definite cyclic pattern in the occurrence of coal lithotypes in vertical order and is similar to that described in Australian and European coal seams. Asymmetrical cyclic sequences are a normal, rather than an unusual condition, within coal seams. It is visualized that a gradual decline of toxic environment and ground water level resulted in the coal lithotype cycles in the Kargali seam of East Bokaro sub-basin. The close interbedding of Vitrain and Clarain is suggestive of seasonal fluctuation in anaerobic and aerobic conditions during peat formation.

• Numerical modelling on fate and transport of petroleum hydrocarbons in an unsaturated subsurface system for varying source scenario

The vertical transport of petroleum hydrocarbons from a surface spill through an unsaturated subsurface system is of major concern in assessing the vulnerability of groundwater contamination. A realistic representation on fate and transport of volatile organic compounds at different periods after spill is quite challenging due to the variation in the source behaviour at the surface of spill as well as the variation in the hydrodynamic parameters and the associated inter-phase partitioning coefficients within the subsurface. In the present study, a one dimensional numerical model is developed to simulate the transport of benzene in an unsaturated subsurface system considering the effect of volatilization, dissolution, adsorption and microbial degradation of benzene for (i) constant continuous source, (ii) continuous decaying source, and (iii) residual source. The numerical results suggest that volatilization is the important sink for contaminant removal considering the soil air migration within the unsaturated zone. It is also observed that the coupled effect of dissolution and volatilization is important for the decaying source at the surface immediately after the spill, whereas rate-limited dissolution from residually entrapped source is responsible for the extended contamination towards later period.

• Optimization method for quantitative calculation of clay minerals in soil

Determination of types and amounts for clay minerals in soil are important in environmental, agricultural, and geological investigations. Many reliable methods have been established to identify clay mineral types. However, no reliable method for quantitative analysis of clay minerals has been established so far. In this study, an attempt was made to propose an optimization method for the quantitative determination of clay minerals in soil based on bulk chemical composition data. The fundamental principles and processes of the calculation are elucidated. Some samples were used for reliability verification of the method and the results prove the simplicity and efficacy of the approach.

• # Journal of Earth System Science

Current Issue
Volume 128 | Issue 8
December 2019

• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019