• Volume 128, Issue 6

August 2019

• Monthly prediction of streamflow using data-driven models

The estimation of river run-off is a complex process, but it is of vital importance to the proper operation of reservoirs, the design of hydraulic structures, flood control, drought management and the supply of water and electricity. The high uncertainty in rainfall–run-off modelling and lack of data has made the development of rainfall–run-off models with acceptable levels of accuracy and precision challenging. Furthermore, the rainfall–run-off models commonly do not provide an explicit relationship between run-off and other variables to be used for run-off-related investigations. To overcome the knowledge and information shortage in rainfall–run-off modelling, data-driven models have been used instead of conceptual models for the development of rainfall–run-off models. In this paper, three data-driven models, the genetic algorithm-support vector regression (GA-SVR), genetic algorithm-artificial neural network (GA-ANN) and the group method of data handling (GMDH) have been used to predict the monthly run-off of the Gavehroud basin. Their performances are compared with a conceptual hydrological model (HYMOD) whose parameters are calibrated using the GA. To this end, the monthly data on precipitation, temperature and run-off at the Gavehroud basin over 49 yr (1960–2009) were analysed. Evaluation of the results using performance evaluation indicators showed that the hybrid model of GA-SVR provided better accuracy in predicting the nonlinear behaviour of flow data than the GA-ANN, GMDH and HYMOD.

• Suppressed biological production in the coastal waters off Visakhapatnam, India under the impact of the very severe cyclonic storm Hudhud

Tropical cyclones generally enhance biological production due to the increase in nutrients input due to vertical mixing. In contrast, the very severe cyclonic storm (VSCS)Hudhud decreased primary production due to the strong stratification associated with torrential rainfall and high suspended load from the major city where the cyclone made landfall. The study region received nutrients from the cold core eddy and coastal upwelling in the offshore and inshore regions, respectively, during pre-cyclone period and the same was suppressed under the influence of cyclonic winds led to convergence by shoreward Ekman transport. The land run-off brought nutrients to the coast during cyclone Hudhud; however, their concentrations were less than that during other cyclones (Orissa supercyclone, Sidr and Phailin). Such low nutrient levels resulted from the VSCS Hudhud crossing the urban region (Visakhapatnam city) whereas other cyclones crossed the coast over fertile agricultural lands which led to high nutrients input associated with phytoplankton blooms. Therefore, the biological response to a cyclone not only depends on the intensity of the cyclone but also on the region of the land it crosses.

• Complexity and periodicity of daily mean temperature and dew-point across India

The complexity of temperature and dew-point fluctuations across India are being investigated and analyzed with the help of recurrence plots (RP) and recurrence quantification analysis (RQA). The results firmly state that both data sets is non-linear, non-stationary and deterministic. Hilbert–Huang transform and an efficient peak detection algorithm (integral method) have been used to detect the underlying periodicity (above 95% CL) within these two signals. The nature of the complexity and the derived periods of these two weather variables show that there are significant impact of the local geographical topology and global atmospheric fluctuations on the overall pattern and fluctuation of the temperature and dew-point profile across India.

• Retrieval of Martian ozone and dust from SPICAM spectrometer for MY27–MY28

Ozone (O$_{3}$) is important in the stabilisation of CO$_{2}$ in the Martian atmosphere and thus it is important to study the spatio-temporal variability of O$_{3}$. We retrieve two years of total columnar O$_{3}$ from raw spectral data provided by the SPectroscopy for the Investigation of the Characteristics of the Atmosphere of Mars (SPICAM) instrument aboard the Mars Express. The seasonal variability is studied in tropical, mid- and high latitudes and is compared with simulations by a photochemical coupled general circulation model (GCM). The high latitudes exhibit the largest seasonal variations in O$_{3}$, with a winter high and a summer low and a comparison with GCM results is good in general. We have studied the correlation of O$_{3}$ with dust, retrieved simultaneously from SPICAM observations. In southern tropical latitudes, the columnar O$_{3}$ is seen to increase during a global dust storm year (Martian year (MY) 28) compared to the O$_{3}$ column values during a year without global dust storm (MY27), although the water vapour column between these years remains unchanged. This indicates the radiative impact of dust on O$_{3}$ and its retrieval. We also study the ozone–carbon monoxide correlation as a tracer of dynamics. The dynamical contribution to the O$_{3}$ column is found to be the highest during winter over the southern polar region.

• Projected changes of inundation of cyclonic storms in the Ganges–Brahmaputra–Meghna delta of Bangladesh due to SLR by 2100

Almost every year, Bangladesh experiences disasters such as tropical cyclones, storm surges, coastal erosion or floods. Tropical cyclones originate from the North Indian Ocean and often cause devastating flood inundations in Bangladesh. Storm surges of the Bay of Bengal (BOB) are larger compared to other regions of the world for similar cyclones due to amplification by the shallow water depth, huge continental shelf and convergent coastlines. This scenario of inundation for such storm surges in the future when the sea level rise (SLR) occurs due to global warming will be different from the present. The densely populated coastal region of Bangladesh is likely to become more vulnerable in the future due to SLR. Disaster risks can be reduced if storm surges can be predicted well ahead. To assess the possible changes of inundation in the future, a widely used coastal model, Delft3D, has been applied for this BOB region. The model has been validated for the storm surge of three recent devastating cyclones, namely, Sidr, Aila and Roanu in the southern coast of Bangladesh. The validated model has been run to produce inundation maps and statistics for cyclonic storm surges such as Sidr, Aila and Roanu and probable SLR. Three possible SLR boundary conditions are chosen from the business-as-usual climate scenario representative concentration pathway 8.5 with values of 0.5 m (lower limit), 1 m (upper limit) and 1.5 m (extreme case, considering the subsidence and a rapid collapse of the Antarctic ice sheet). It is found that a category 4 cyclone such as cyclone Sidr would inundate 2.6%, 3.67% and 5.84% of the area of the country if the SLR is 0.5, 1 and 1.5 m, which will affect the livelihood of nearly 4.1, 7.0 and 9.1 million people of Bangladesh, respectively. It will also inundate up to 21.0%, 42.1% and 65.1% of the Sundarbans mangrove forest, which will undoubtedly affect the ecology of this unique ecosystem.

• Noise characteristics of GPS time series and their influence on velocity uncertainties

Accurate geodetic crustal deformation estimates with realistic uncertainties are essential to constrain geophysical models. A selection of appropriate noise model in geodetic data processing based on the characteristics of the geodetic time series being studied is the key to achieving realistic uncertainties. In this study, we report noise characteristics of a 12-yr long global positioning system (GPS) geodetic time series (2002–2013) obtained from 22 continuous mode GPS stations situated in north-east India, Nepal and Bhutan Himalayas which are one of the most complex tectonic regimes influenced by the largest hydrological loading and impacted with a load of the largest inland glaciers. A comparison of the maximum log likelihood estimates of three different noise models – (i) white plus power law (WPL), (ii) white plus flicker law (WFL) and (iii) white plus random walk noise – adopted to process the GPS time series reveals that among the three models, $\sim$74% of the time series can be better described either by WPL or WFL model. The results further showed that the horizontals in Nepal Himalayas and verticals in north-east India are highly correlated with time. The impact analysis of noise models on velocity estimation shows that the conventional way of assuming time uncorrelated noise models (white noise) for constraining the crustal deformation of this region severely underestimates rate uncertainty up to 14 times. Such simplistic assumption, being adopted in many geodetic crustal deformation studies, will completely mislead the geophysical interpretations and has the potential danger of identifying any inter/intra-plate tectonic quiescence as active tectonic deformation. Furthermore, the analysis on the effect of the time span of observations on velocity uncertainties suggests 3 yr of continuous observations as a minimum requirement to estimate the horizontal velocities with realistic uncertainties for constraining the tectonics of this region.

• Climatic changes over the Arabian Peninsula and their correlation with Indian rainfall

The summer monsoon rainfall affects most of the population of the Indian subcontinent. A slight variation of strength and spatial distribution in monsoon rains has huge societal impacts. So understanding the significance of its variability and the factors that control this variability is an imperative task. The Indian monsoon (also regarded as a global phenomenon) varies with the global climatic components like geopotential height, sea surface temperature, outgoing long-wave radiation and mean sea level pressure. The paper presents a statistical analysis of rainfall (over India) and climatic components (over the Arabian Peninsula) and the relationship between them. The period (1979–2013) shows a decrease in monsoon rainfall over the country. During this period, there was an increase in the tropospheric temperature over the Arabian Peninsula. Rainfall showed a direct relationship with the tropospheric temperature and thickness that gets stronger during the period (1979–2013). Except for the northeastern region of India, the rest showed a strong positive correlation with the middle and upper tropospheric temperature over the Arabian Peninsula while the lower tropospheric temperature showed a weak relationship. However, this correlation gets weakened during the El Nino and La Nina years. The findings will be helpful to enhance the Indian rainfall variation and the climatic factors responsible for this variation.

• Landslide stability assessment along Panchkula–Morni road, Nahan salient, NW Himalaya, India

We report the slope stability analysis of three vulnerable sites (S1, S2 and S3) within the lower Siwalik along the Panchkula–Morni road section in the Nahan salient, north-western Himalaya. Kinematic analysis of joint data was conducted to understand the different modes of failure. Rock mass classification techniques like rock mass rating, slope mass rating (SMR) and continuous SMR were used for stability classification and the factor of safety was calculated using stability charts. At site S1, the instability is controlled by the orientation of the discontinuity joint J1 which is parallel to the bedding and at site S2, the slope fails due to the wedge. The Umri landslide site S3 is the product of a damage zone by the normal faults which intersect at joint J3; a wedge is formed which falls in the critical zone. The damage zone in the Umri landslide greatly affects the porosity and permeability of the rockmass and acts as a pathway for the percolation of water during rainfall which reduces effective stress. The slope failures are tectonically controlled results due to the high slope angles, structural discontinuities like joints and faults and structural damage zones associated with the faults.

• The impacts of the approaching western disturbances (WDs) on the surface meteorological variables over the north-west Himalaya (NWH), India

Eastward-moving upper air troughs in the subtropical westerlies, commonly known as the western disturbances (WDs) in the Asian subcontinent, are primary sources of precipitation over the north-west Himalayan (NWH) region and the northern plains of India during winter. Many simulation case studies with the help of numerical weather prediction models and a few observational case studies have been conducted to understand the spatial structure, dynamics, energy and weather associated with the WDs over the NWH in the past. However, studies using in situ observations on the impacts of the approaching WDs on various surface meteorological variables at a local scale in the high-altitude mountainous regions of the NWH are lacking. The objectives of this study are to examine the impacts of the approaching WDs on various surface meteorological variables for 11 stations in the NWH and the associated precipitation amount in a 24-hr time interval. Changes (departures) in the values of various meteorological variables are examined on the first precipitation day of the occurrence of active WDs to study the impacts of the approaching WDs and the associated precipitation amount in the 24-hr time interval which are found to depend on the altitude and geographic location of a station. The mean drop in the maximum and ambient air temperatures are found to be 2.0$^{\circ}$ and 0.7$^{\circ}$C, respectively, while the mean rise in the minimum air temperature was found to be 0.8$^{\circ}$C. A mean drop in the surface atmospheric pressure and a mean increase in the relative humidity are found to be 0.9 hPa and 19.5%, respectively, in a 24-hr time interval. The mean precipitation amount and mean maximum precipitation amount associated with the active WDs in the 24-hr time interval are found to be 8.9 and 68.8 mm, respectively. The results are briefly discussed in the paper. The findings of this study can be useful for operational weather forecasting and a selection of precursor variables for developing a real-time local scale weather forecast model(s) for remote areas of the NWH for the winter season.

• Palaeostress and magma pressure measurement of granite veins in the Neoproterozoic Ambaji granulite, South Delhi terrane, Aravalli–Delhi mobile belt, NW India: Implication towards the extension-driven exhumation of the middle–lower crustal rocks

Neoproterozoic Ambaji granulite, in the South Delhi terrane (SDT) of the Aravalli–Delhi mobile belt (ADMB), is multiply deformed at different stages of its exhumation from the middle–lower crust. It was intruded by four phases of granites, G$_{0-3}$, of which the G$_{3}$ was syntectonic with brittle shearing. The orientation of the G$_{3}$ granite veins was used, in this paper, to measure the palaeostress and magma pressure during its intrusion. The G$_{3}$ granite has a porphyritic texture with quartz, microcline and biotite minerals and contains magmatic foliation; biotites are aligned oblique to such foliation, suggesting the syntectonic intrusion of the granite with normal faulting. Stereoplot of the poles of the granite veins shows concentration in the NW and SW quadrants and lack data over an elliptical area at the centre, indicating a girdle pattern. This implies that the magma pressure $P_{\rm{m}}$ > $\sigma _{2}$, compression $\sigma _{1}$ was vertical and extension $\sigma _{3}$ was NW–SE horizontal. Values of $\theta_{2}$ = 16$^{\circ}$ and $\theta_{3}$ = 40$^{\circ}$ were obtained from the stereoplot, used to calculate stress ratio $\Phi$ = 0.81, driving pressure $R^{\prime}$ = 0.92 and the construction of the 3D Mohr plot for $P_{\rm{m}}$ and principal stresses. Result suggests that the $G_{3}$ granite intruded under extensional tectonics that probably contributed to the exhumation of the Ambaji granulite.

• Factors controlling stable isotopes variability in precipitation in Syria: Statistical analysis approach

The major characteristics of the stable isotopes ($^{18}$O and $^{2}$H) and deuterium excess (d-excess or d) of rainfall samples collected from 16 stations during two periods (1989–1993 and 2003–2006) were statistically analysed to understand the factors controlling the temporal and spatial isotope variability in precipitation (P) in Syria. Rainfall waters at the mountainous regions are remarkably the most depleted in heavy stable isotopes, with also high d-excess values (d>20 per thousand). The enriched rainfall waters (lower d-excess values), mostly referring to coastal and some inland areas, are subject to the evaporation of falling raindrops. Rainfalls at the southern stations have impressively the highest d-excess values (d > 22 per thousand), likely because of intensive interactions with the Mediterranean Sea (MS) moistures. The temperature (T) effect, shown by an average $\delta^{18}$O gradient of $\approx$0.34 $\pm$ 0.03 per thousand/$^{\circ}$C, is very close to the Global Network for Isotopes in Precipitation value (0.3 per thousand/$^{\circ}$C). The altitude effect, represented by a $\delta^{18}$O gradient of −0.18 $\pm$ 0.03 per thousand/100 m, fits well with the range given for most Mediterranean countries. Relative humidity (RH) and P-amount effects are characterised by an isotopic depletion, with a notable rise in the d-excess value with P and RH increases. The seasonal effect is shown by depleted $\delta^{18}$O and $\delta^{2}$H values during December–February and enriched $\delta^{18}$O and $\delta^{2}$H values at the end of April, with frequently low d-excess values (<8 per thousand). T parameter seems to be the major factor that strongly controls the variability of the stable isotope compositions of P in Syria. The moisture from the MS and secondary evaporation conjunctly play additional roles, but of less importance than the T effect.

• Groundwater potential assessment of the Sero plain using bivariate models of the frequency ratio, Shannon entropy and evidential belief function

The goal of the present research is to evaluate three bivariate models of the frequency ratio, Shannon entropy (SE) and evidential belief function in the spatial prediction of groundwater at the Sero plain located in west Azerbaijan, Iran. In the first phase, well locations with groundwater yields >11 m$^{3}$/hr were identified (75 well locations). Ten groundwater conditioning factors affecting the occurrence of groundwater, namely, altitude, slope degree, curvature, slope aspect, rainfall, soil, land-use, geology and distance from the fault and the river, were selected for modelling. Finally, the groundwater potential map results were drawn from three implemented models and they were validated using testing data by area under the receiver operating characteristic curve (AUC). The AUCs of these models were 0.84, 81 and 85%, respectively. The results of the current study demonstrated that these models could be successfully employed for spatial prediction modelling. Moreover, the results of the SE model demonstrated that the most and the least important factors in groundwater occurrences in the area under study were altitude, curvature and rainfall, respectively. The results of this study are helpful for the Regional Water Authority of Urmia and the decision makers to comprehensively assess the groundwater exploration development and environmental management in future planning.

• Landslide susceptibility mapping of the Tehri reservoir rim area using the weights of evidence method

This study was aimed to utilise important landslide causal factors for the delineation of the landslide susceptible area using the weights of evidence (WofE) method in the Tehri reservoir rim region on a macro scale. The Tehri reservoir extends up to 70 km and bounded by moderate to steep slopes. Landslide susceptibility mapping (LSM) is an essential measure for identifying the potentially unstable slopes bounding the reservoir. With the help of ancillary data, remote sensing imagery and a digital elevation model, 10 causative factors along with landslide inventory were extracted. Initially, the WofE model was applied to obtain the association between landslides and causative factors. The process gave the numerical estimate of correlation between landslides and causative factors by means of positive and negative correlation. Important factor attributes, potentially causing landslides, were identified based on high positive correlation values. Later, the posterior probability of landslide occurrence for each mapping unit was also computed using the WofE model. Posterior probability was divided into five relative susceptibility classes. Validation of the posterior probability map was carried out by using the prediction rate curve technique and a reasonable accuracy of 83% was achieved. LSM of the Tehri reservoir rim area implicates unplanned road construction and settlements coupled with the reservoir slope settlement process for the present degradation of the geo-environmental system in that region.

• Numerical simulation of groundwater flow and temperature distribution in Aegean Coast of Turkey

Geological studies indicate that one of the most important geothermal systems of Turkey is located in the western Anatolia. There are plenty of studies covering the geological, geophysical and modeling aspects on land. In this study, for the first time, we construct coupled numerical models of fluid flow and temperature offshore Gulf of Izmir and Seferihisar–Doganbey, using constraints from marine seismic data, which reveal pockmarks, mud volcanoes, and fluid vents. The numerical models were designed by taking into account of main tectonic structures such as Izmir Fault, Doganbey Fault, Tuzla Fault and Seferihisar Horst. It is found that hydrothermal circulation pattern is influenced by the combination of presence of faults, sediment thickness and seafloor bathymetry. The models here give new insights into the future studies on the possible fluid transport mechanisms.

• Performance of a very high-resolution global forecast system model (GFS T1534) at 12.5 km over the Indian region during the 2016–2017 monsoon seasons

A global forecast system model at a horizontal resolution of T1534 ($\sim$12.5 km) has been evaluated for the monsoon seasons of 2016 and 2017 over the Indian region. It is for the first time that such a high-resolution global model is being run operationally for monsoon weather forecast. A detailed validation of the model therefore is essential. The validation of mean monsoon rainfall for the season and individual months indicates a tendency for wet bias over the land region in all the forecast lead time. The probability distribution of forecast rainfall shows an overestimation (underestimation) of rainfall for the lighter (heavy) categories. However, the probability distribution functions of moderate rainfall categories are found to be reasonable. The model shows fidelity in capturing the extremely heavy rainfall categories with shorter lead times. The model reasonably predicts the large-scale parameters associated with the Indian summer monsoon, particularly, the vertical profile of the moisture. The diurnal rainfall variability forecasts in all lead times show certain biases over different land and oceanic regions and, particularly, over the north–west Indian region. Although the model has a reasonable fidelity in capturing the spatio-temporal variability of the monsoon rain, further development is needed to enhance the skill of forecast of a higher rain rate with a longer lead time.

• Geology, mineralogy and mineral chemistry of the NYF-type pegmatites at the Gabal El Faliq area, South Eastern Desert, Egypt

The Gabal El Faliq area is located in the Eastern Desert of Egypt and belongs to the Wadi Hafafit–Wadi Ghadir fold belt. Lenses and dykes of rare metal-bearing pegmatites occur along major weak zones in the area (Wadi El Gemal strike-slip and its Riedel shears), by which they are structurally controlled. These pegmatites are mineralogically complex. Moreover, they are zoned, and the intermediate zones of the pegmatite varieties contain high amounts of zircon, fergusonite-(Y), columbite-(Fe), allanite-(Ce), xenotime-(Y), monazite-(Ce and Nd), thorite and gummite. These minerals carry Zr, rare earth element (REE), Nb, Ta, Th, U > Ta, F, and they are classified into rare-metal pegmatites, specifically, the niobium, yttrium and fluorine (NYF) enrichment family. The geochemistry aspects of these pegmatites indicate Zr up to 28,984 ppm, Hf up to 1171 ppm, REE up to 19,206 ppm, Nb up to 9962 ppm, Ta up to 152 ppm, U up to 565.5 ppm, Th up to 850 ppm and Ga up to 90 ppm. They were formed under an intracontinental tectonic setting from a basaltic magma similar to the oceanic island basalts (OIBs) contaminated with the crust. Consequently, this study could be used as a guide for the exploration of rare metals in similar regions of the world.

• Isostasy and crustal structure of the Chagos–Laccadive Ridge, Western Indian Ocean: Geodynamic implications

The Chagos–Laccadive Ridge (CLR), a prominent linear aseismic ridge in the Western Indian Ocean is believed to be a trace of the Reunion hotspot. In order to understand the mode of emplacement of this ridge and the nature of the underlying crust, we carried out three-dimensional (3D) flexural modelling and coherence analysis of satellite-derived gravity and bathymetry data along the ridge. The analysis revealed variations in Effective Elastic Thickness ($T_{\rm{e}}$) along the CLR. While the northernmost part of CLR is associated with low $T_{\rm{e}}$ of 3 km with a subsurface to surface loading ratio ($f$) of 1, towards the south, the Maldive Ridge and the Chagos Bank have a fairly uniform $T_{\rm{e}}$ of 8–10 km with a very low loading ratio $f$ of 0.1–0.2. We consider the Laccadive Ridge as a continental sliver possessing underplated magmatic rocks caused by the Reunion hotspot volcanism. The Maldive Ridge and the Chagos Bank appear to have emplaced on a lithosphere of intermediate strength possibly on the flanks of the Central Indian Ridge.

• Cinder cone morphometry in relation to gravity anomaly zones in the Harrat al Birk and Asir foreland, SW Saudi Arabia

The Harrat al Birk (HAB) of the alkali basalts of the post-Miocene age erupted through a thick Precambrian crust along the Red Sea coast. The 200 cinder cones scatter within HAB and three distinct Bouguer anomaly zones are identified as the coastal gravity high (CGH), axial gravity low (AGL) and a gravity high further east Jabal As-Sawda gravity high (JSGH). Interpreted satellite imagery for 150 sizeable cinder cones in three gravity anomaly zones (134 (90%) in CGH, 10 (6%) in AGL and 6 (4%) in JSGH) are morphologically analysed. The juvenile cinder cones (age <1 Ma) are characterised by sub-vertical slope angles (<40$^{\circ}$) with a variable average geomorphic slope, 27$^{\circ}$–40$^{\circ}$ in JSGH, 25$^{\circ}$ in AGL and 2$^{\circ}$–15$^{\circ}$ in CGH. The oldest cones of JSGH display a high $H_{\rm{co}}$/$W_{\rm{co}}$ ratio with angular asymmetry at their base angles. The major feeder lineaments/faults are oriented NNW–SSE to NW–SE, and they supply volcanic material to cinder cones within a distance of 2 km. The results, when integrated with geological maps and gravity profiles, provide a probable root-plumbing system of the volcano edifice. HAB is the produce of the volcanic process from the source area in JSGH that hosts the major cinders, where the tertiary gabbroic dyke zone acts as a vertical magma sheet for the cinders.

• Monitoring urban land surface deformation (2004–2010) from InSAR, groundwater and levelling data: A case study of Changzhou city, China

Land deformation caused by the overexploitation of groundwater has become a potential geological hazard in Changzhou, China. To reduce the potential damage from deformation disasters, it is quite necessary to monitor them. In this study, C-band ENVISAT ASAR synthetic aperture radar (SAR) datasets acquired from 2004 to 2010 were processed with the small baseline subset (SBAS) interferometric SAR (InSAR) method to investigate the spatial–temporal distribution of land deformation. Levelling survey data were used to assess the deformation accuracy measured by the InSAR method, and groundwater level data were used to analyse the incentives for deformation. The SBAS InSAR results found several subsidence regions in the Wujin district and the central part of the Zhonglou district. The annual deformation rate calculated from the C-band interferograms ranged from −65 to +35 mm/yr in the line of sight (LOS) direction, and the cumulative subsidence ranged from −0.35 to 0.13 m in the vertical direction. The levelling survey data show that the two measurements are generally consistent. Correlation analysis between the groundwater table and InSAR measurements at six groundwater well stations shows that groundwater recharges can cause land rebound within the Changzhou urban region. However, subsidence was also observed simultaneously with a rising water table, which might have been caused by the status of consolidation of the strata. Our study provides scientific evidence on the management of groundwater extraction and the assessment of land-subsidence hazard.

• A comparative analysis due to the effect of point source on generation of SH wave

The propagation of SH wave in a heterogeneous initially stressed viscoelastic layer lying over a heterogeneous initially stressed orthotropic half-space due to a point source is analysed mathematically. The dispersion equation of SH wave is obtained for the propagation of SH wave in a specified model. The method of Green’s function and Fourier transformation is incorporated to obtain the dispersion equation. The curves of dispersion equation are sketched for various values of heterogeneous parameters and initial stress on angular frequency, phase velocity and damping velocity in respect of wave number. The dispersion equation is derived for some special cases which reduces to the classical equation of Love-type wave. The present study reveals the effect of heterogeneous parameter and initial stress associated with both viscoelastic and orthotropic media.

• Integrated geophysical investigations in the Mudiyawas–Khera block of the Alwar basin of North Delhi Fold Belt (NDBF): Implications on copper and associated mineralisation

Mundiyawas–Khera area of the Alwar basin in the North Delhi Fold Belt is well known for copper and associated gold mineralisation hosted within the felsic volcanic rocks. Gravity and magnetic surveys were conducted over the established mineralised blocks covering an area of $\sim$8 km$^{2}$ in the study regions and these data were interpreted using the Euler deconvolution and 2D potential field modelling to determine the subsurface geometry and depth extent of the ore body. The geophysical signatures in this area reveal three prominent anomalous zones in corroboration with the surface geology and drill hole data. Although basic/mafic rocks have not been found within the area, the observed strong residual gravity high ($\sim$4.0 mGal) and residual magnetic high closures ($\sim$90 nT) in the Mundiyawas block could be due to the cumulative effect of small-scale structural domes and the occurrence of sulphide mineralisation especially in the form of massive pyrrhotite. Moderate magnetic anomalies without appreciable gravity anomalies over the main copper-bearing zones in the Khera block are possibly due to the disseminated form, vein fillings and stringers of chalcopyrite, arsenopyrite and minor pyrrhotite hosted within the felsic volcanic rocks. The results of Euler depth solutions over these anomalous zones are found to vary from 50 to 250 m. Further, the subsurface geometry obtained across the Mundiyawas block through joint gravity and magnetic modelling constrained with drill hole information clearly depicts the presence of sulphide ore body having a width of 30–80 m within the carbon phyllite and tremolite-bearing dolomite. Combining the geophysical signatures noticed along the lithocontacts with the available geochemical and mineralogical observations of drill hole samples, we further confirm the strata-bound nature of sulphide mineralisation in the Mundiyawas–Khera area and it is controlled by both lithology and structural geometry of the host rocks.

• Earthquake-induced soft sediment deformation (SSD) structures from the Bilara limestone formation, Marwar basin, India

The Neoproterozoic Bilara limestone Formation of the Marwar Group, Rajasthan, India exposes metres-thick layers of soft sediment deformation (SSD) structures at different stratigraphic levels which could be traced over hundreds of metres on the outcrop scale. The SSD structures include disharmonic folds, low-angle thrusts, distorted laminae, fluidisation pipes, slump and load structures, homogeneities, diapirs, etc. Whereas SSD structures suggesting tensional stress, viz., intrastriatal graben, fluidisation, slump, etc. dominate in the lower part of the Bilara succession, features implicating compression, viz., folds, low-angle thrust are prevalent in the uppermost part. Since SSD structures are mostly confined within the algal laminites, we interpret that enhanced micritic fluid pressure below early cemented algal carbonate played a major role in laminae deformation. Depending on the degree of lithification and pore-water pressure, deformation features formed either plastically or led to diapiric injection at enhanced pore water pressure. Separated by near-horizontal underformed strata, the SSD layers, traceable over hundreds of metres, are interpreted as products of seismic shacking. Considering the time frame of the Marwar basin, i.e., the Precambrian–Cambrian transition, the SSD horizons present within the Bilara succession may hold the potential for the correlation with SSD structures reported from the time-correlative stratigraphic successions present in erstwhile adjoining tectonic terrains, e.g., China, Siberia, etc.

• Estimation of gas hydrate saturation using isotropic and anisotropic modelling in the Mahanadi basin

A base of gas hydrate stability zone was established after coring and drilling under the National Gas Hydrate Program (NGHP) Expedition-01 in the Mahanadi basin. At two sites, logging-while-drilling log data, and, at one site, wireline log data, were acquired during the NGHP Expedition-01. Gas hydrate reservoirs modelling can be performed in two different ways. One way is isotropic (load bearing) and, on the other hand, anisotropic media (fracture filling with gas hydrate). Here, we have performed anisotropic modelling and estimated gas hydrate saturation using P-wave velocity, assuming an incidence angle of 75$^{\circ}$ represents the vertical fracture. The estimated gas hydrate saturation at sites NGHP-01-08 and NGHP-01-09, assuming anisotropic media, reduces the estimate by half compared to the saturation estimation by assuming isotropic media. The saturation at site NGHP-01-19 estimated from the isotropic and anisotropic P-wave velocity models are more or less similar except in the zone (175–210 m) just above the bottom simulating reflector depth, and this zone shows similar reduction in saturation as estimated at sites NGHP-01-08 and NGHP-01-09. Observations show that average gas hydrate saturations are relatively low (up to 5% of the pore space). The saturation of a gas hydrate estimated from an isotropic P-wave model varies from 5% to 20%. However, the saturation estimated from the anisotropic P-wave model shows a variation up to 10% of the pore spaces at three sites.

• Characteristic parameters of positive cloud-to-ground lightning channel

The high time-resolved spectra of two natural positive cloud-to-ground (CG) lightning of which one of them contains multiple return strokes have been taken by a high-speed slit-less spectrograph. On combining with the synchronous electric field change waveform, the temperature, electrical conductivity of the return stroke channel, radius of the core current channel and the peak value of current are calculated. The correlation between the peak current and the time interval of five M components which overlapped with the continuous current following the subsequent return stroke R1 of multiple return strokes positive CG lightning were analysed. The results show that the average temperatures of the return stroke channels for two positive CG lightning are about 28,900–29,800 K, the radius of the core current channel is about 0.36–1.01 cm, the estimated peak currents of the return strokes are about 18.6–38.0 kA, which are all larger than the typical values of common negative CG lightning. The peak currents of the M components are positively correlated with the time intervals between them.

• Petrographic studies to delineate suitable coal seams for coal liquefaction and their palaeo-environmental analysis: A case study from the Ib river and Mand-Raigarh coalfields of the Mahanadi valley coalfields, India

A systematic approach has been carried out to delineate the coal seam zones from the Ib river coalfield, Odisha and the Mand-Raigarh coalfield, Chhattisgarh for the conversion of coal to oil as well as to establish the peat-forming environment of the mire and determine the depositional facies analysis of the coal seams. Zone R-I of Raniganj formation and Belpahar, Parkhani and Lajkura of Barakar formation from the Ib river coalfield and Seam nos. VII, VI, III and I of the Barakar formation from the Mand-Raigarh coalfield are identified based on their high percentage of liptinite and reactive content as well as their suitable maturity (mostly sub-bituminous rank) as potential for coal-to-oil conversion. The palaeo-depositional environment for peat formation has been constructed using the tissue preservation index and gelification index following coal facies analysis which shows that the peat formation in the Ib river coalfield took place under limnic to limno-telmatic conditions with prolonged wetness in the mire, whereas in the Mand-Raigarh coalfield, peat evolved under a clastic to an open marsh limnic environment with intermittent wet and dry spells. The microlithotype composition indicates that both the coalfields evolved under lower to upper deltaic settings.

• The impact of crop residue burning (CRB) on the diurnal and seasonal variability of the ozone and PM levels at a semi-urban site in the north-western Indo-Gangetic plain

Ozone and particulate matter (PM), PM$_{10}$ and PM$_{2.5}$, were monitored along with meteorological parameters at a semi-urban location, Patiala, in the north-western Indo-Gangetic plain from December 2013 to November 2014. The annual mean concentration levels of PM$_{10}$, PM$_{2.5}$ and ozone were recorded as 178 $\mu$g m$^{-3}$, 88 $\mu$g m$^{-3}$ and 39 ppb, which also exceeded the national standards on a 24-h average basis, by 77.3% (335 days), 53.2% (338 days) and 20 days, respectively. High levels of PM (PM$_{10}$ and PM$_{2.5}$) were observed in winter (58–381 and 42–270 $\mu$g m$^{-3}$) and in the post-monsoon (71–320 and 39–320 $\mu$g m$^{-3}$) season and a rise in the level of ozone was observed in summer (22–72 ppb) and in the post-monsoon season (23–73 ppb), respectively. The rate of ozone production was the highest during the post-harvest fire period (3.94 ppb O$_{3}$/h in May and 4.23 ppb O$_{3}$/h in November). A Pearson correlation study showed the strong dependency of PM and ozone on meteorological variables. Relative humidity has the highest ranking for ozone and PM$_{10}$, while wind speed has the lowest rank for ozone, PM$_{10}$ and PM$_{2.5}$ in the order of factors affecting the level of pollutants. The generalised linear model and the neural network model (for ozone) and the random forest model (for PM) outperformed on the basis of performance indices and further cross-validation was done.

• Pb isotope geochemistry of the late Miocene–Pliocene volcanic rocks from Todeshk, the central part of the Urumieh–Dokhtar magmatic arc, Iran: Evidence of an enriched mantle source

The late Miocene–Pliocene volcanic rocks from Todeshk, south-east of Isfahan, are located in the middle of the Urumieh–Dokhtar magmatic belt. The belt is considered the subduction-related magmatic arc. The late Miocene–Pliocene calc-alkaline volcanic rocks are mainly andesite and dacite. The rocks have been formed during the post-collisional stage of the Zagros orogen. Geochemical data show the enrichment of light rare-earth elements and large ion lithophile elements such as Cs, Rb, K, Pb, Ba and Th as well as the depletion of elements with high field strength such as Nb, Ta and Ti. The Pb–Sr–Nd isotopic ratios of the studied rocks are characterised by $^{206}$Pb/$^{204}$Pb =18.41–18.72; $^{207}$Pb/$^{204}$Pb =15.64–15.67; $^{208}$Pb/$^{204}$Pb = 38.49–38.83; $^{207}$Pb/$^{206}$Pb = 0.8372–0.8496; $^{208}$Pb/$^{206}$Pb = 2.0743–2.0905; $^{87}$Sr/$^{86}$Sr = 0.7051–0.7068 and $^{143}$Nd/$^{144}$Nd = 0.5125. The rocks have $\Delta$7/4Pb = 15.44–15.82 and $\Delta$8/4Pb = 57.26–60.44. Based on petrological studies and the whole rock Pb, Sr and Nd isotopes data, the late Miocene–Pliocene calc-alkaline volcanic rocks have been generated from the partial melting of the subduction-related metasomatised mantle. Additionally, the slab-derived melts and fluids were recycled into the mantle source. The data demonstrate that terrigenous sediments accompanied by a subducted slab play an important role in the formation of the enriched mantle as the source of volcanic rocks.

• Evaluation and characterization of groundwater of the Maastrichtian Lafia formation, Central Benue trough, Nigeria

Hydrochemical assessment of groundwater in the Lafia formation, Central Benue trough, Nigeria was carried out with the aim of determining its quality for domestic and irrigation purposes. Thirty groundwater samples from boreholes and hand-dug wells were analyzed using atomic spectrometry and titrimetric methods. The water quality index (WQI) was evaluated from physicochemical parameters and used in assessing the groundwater quality for drinking, while the electrical conductivity (EC), percentage sodium (%Na), sodium absorption ratio (SAR) and magnesium hardness (MH) were evaluated to assess its suitability for irrigation. The physico-chemical parameters in order of dominance are HCO$_{3}^{-}$ > NO$_{3}^{-}$ > Cl$^{-}$ > PO$_{3}^{-}$ > SO$_{4}^{2-}$ for the anions and Fe$^{3+}$ > Na$^{+}$ > Ca$^{2+}$ > Mg$^{2+}$ > Pb$^{2+}$ > K$^{+}$ for the cations. The pH indicates acidic to weakly alkaline water (5.1–7.3); EC ranges from 110 to 1396 $\mu$S/cm, while the total dissolved solids range between 136.9 and 3.4 mg/l, based on which it is classified as freshwater. WQI showed that only 40% of the groundwater samples are suitable while 60% are unsuitable for drinking and will therefore require treatment. Three water facies: Ca$^{2+} +$ Mg$^{2+}$, Ca$^{2+} +$ Na$^{+} +$ K$^{+}$ and HCO$_{3}^{-}$ characterized the area indicating the groundwater-quality situation. Based on EC classification, 33.33% of the water samples are considered excellent, 60% as good, 6.67% as permissible while on the basis of %Na, only 13.34% are unsuitable for irrigation. SAR of 96.67 and 3.33% of the groundwater samples indicate excellent and doubtful waters, respectively. 93.4% of groundwater samples has MH < 50 and are considered suitable for irrigation.

• Microseismic monitoring application for primary stability evaluation of the powerhouse of the Tapovan Vishnugad Hydropower Project

The study of micro-cracks, shear zone and redistribution of stress after excavation in the rockmass is required for a stability analysis of the underground structure. The powerhouse of the Tapovan Vishnugad Hydropower Project (TVHPP) of NTPC Ltd. is located in the seismic zone V of India and is positioned at the junction of the middle and higher Himalayan region under challenging geological conditions. The powerhouse cavern constructed by drill and blast method encountered a number of rockbursts of various intensities during and after construction. So, a real-time remote microseismic monitoring network was used to evaluate the stability of the powerhouse cavern rockmass. Strata condition, rockburst occurrence during construction and drilling feasibility for sensor installation were studied for an array of designs of the microseismic monitoring network. The primary monitoring period demarcated the micro-crack locations and probable failure zones in the powerhouse rockmass by processing and analysis of various temporal and spatial variations of microseismic parameters to evaluate the underground powerhouse structural stability. Although a large number of microseismic events occurred in the powerhouse which resulted in high displacement in a few areas, due to the low amount of energy released from the events occurring inside the powerhouse, the structure appears to be stable.

• Sensitivity of aerosol radiative forcing to various aerosol parameters over the Bay of Bengal

In the shortwave solar spectrum (0.25-5 $\mu$m), radiation is affected by the change in various aerosol properties and also by water vapour and other gas molecules. The presence of a variety of aerosols over the Bay of Bengal (BoB) during different seasons results in a change in aerosol properties, including the aerosol layer height. The BoB is an integral part of the Indian monsoon, and hence it is essential to understand the radiation budget over the BoB. The sensitivity of the aerosol forcing due to the changes in aerosol properties and other parameters has been studied using the Santa Barbara discrete ordinates radiative transfer model. The aerosol forcing at the top of the atmosphere was found to depend on the aerosol loading (aerosol optical depth), aerosol type (single scattering albedo) and the angular distribution of the scattered radiation (asymmetry parameter). The analysis also shows the presence of a relationship between aerosol layer height and the total amount of water vapour present in the atmosphere. The present study highlights the need for better retrievals of vertical aerosol distribution and water vapour profiles for a better understanding of the role of aerosols in the climate.

• # Journal of Earth System Science

Volume 129, 2020
All articles
Continuous Article Publishing mode

• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019