• R N SINGH

Articles written in Journal of Earth System Science

• Measurements of reflection coefficients of stratified layers using X-band bistatic scatterometers

Laboratory modelling of earth’s subsurface stratification has been carried out using X-band microwave bistatic scatterometer system. Look angle variation of reflectivity for various subsurface layers under dry and wet conditions have been measured. From measured reflectivity data and the reciprocity theorem the emissivity and the brightness temperature variations have been computed, and the data are in good agreement with reported results. The importance of laboratory and field measurements and its remote sensing application has been discussed.

• Inverse problem for the determination of the bounds on the mantle heat flow

This paper presents a method for determining the nature of the spatial structure of the heat flow anomaly at depth given a few observations of surface heat flow. We use the constraint of the positivity of the heat flow throughout the domain under consideration to arrive at the solution. Both Parker’s ideal body and linear programming approaches have been considered. We find that a few measurements are able to give a reasonable good estimation of the heat flow anomaly at depth. The method has been applied to a real case in the French Massif Central. Results point to the presence of enhanced basal heat flow anomaly.

• Generation of low-frequency oscillations in the subsolar venus ionopause

The steep electron density gradient, the magnetic field curvature and the effect of gravity make the Venus ionopause region unstable. The onset of flute instability in the Venus ionopause plasma has been studied. The dispersion of waves and their growth have been studied using in situ measured data. The existence of low frequency waves in the subsolar magnetic field data ionopause region has been interpreted to arise as the result of flute instability.

• Gravity induced near-surface stresses in long-symmetric ridge-valley systems

Patterns of near-surface gravity and tectonically-induced stresses within ridge-valley systems greatly illuminate our understanding of important geodynamic processes as well as design of experiments to elucidate them. This paper presents analytical results derived for a number of geometrical configurations and range of mechanical properties of a ridge-valley system using the elastic solution of McTigue and Mei. The study reveals (i) the presence of non-zero compressive stresses near the ridge crests, which decrease with increasing Poisson's ratio (μ) and reduce to zero at ridge crests for μ=0·5 and that (ii) the central tensional regime characterizing a valley becomes narrower due to the presence of two ridges; and decreases with increasing μ, becoming compressive at depth. For all geometrical parameters considered, all components of stress show concentration at the outer flanks of the ridges and increase with depth approaching a standard state of stress.

• Rheological thickness and strength of the Indian continental lithosphere

The estimates of rheological thickness and total lithospheric strength for the Indian continental lithosphere have been obtained based on the representative rheological properties of upper crust, lower crust and upper mantle, and some of the available heat flow and heat generation data. The rheological thickness, computed at different locations in the Indian shield, shows lateral variation ranging from 79km in the southern part to 65 km in the northern part for a strain rate of 10-14 s-1. The total strength of the continental lithosphere is of the order of 1013 Nm-1 for the same value of strain rate and decreases northward. The computations carried out for a range of strain rates show an increase in the rheological thickness and strength of the lithosphere with increasing strain rate. These results would be important in understanding the flexural response of the Indian continental lithosphere to surface and subsurface loading, and response to tectonic forces acting on it.

• Effects of transient uplift/erosion on the surface heat flow and heat generation relationship in presence of small scale asthenospheric convection

In this paper the effect of transient uplift/erosion on the relationship between surface heat flow and heat generation for truncated exponential model of radiogenic heat source distribution and basal asthenospheric convection is investigated. Asthenospheric convection is described by a parameterized model, in the form of a nonlinear heat flux boundary condition involving basal temperature and mantle internal temperature. This boundary condition has been linearized and the analytical solution of the problem is obtained by the eigenvalue-eigenfunction expansion method. The analytical solution is used to derive the nature of surface heat flow and heat generation relationship. The results show that the linear relationship is maintained during the uplift/erosion and the estimates of the slope of the linear relationship are different from the depth scale of the exponential model and increase with the rate of uplift/erosion. The estimates of the reduced heat flow also increase with the rate of uplift/erosion. These results would find applications in the interpretation of linear surface heat flow and heat generation relationship which is observed in different tectonic environment.

• Three-dimensional intraplate stress distributions associated with topography and crustal density inhomogeneities beneath the Deccan Volcanic Province

The generation of intraplate earthquakes has been attributed to perturbations in the stress regime, either due to surface and sub-surface loading or strength weakening of the rock mass. The present work aims at estimating the intraplate stresses associated with topography and crustal density inhomogeneities beneath the Deccan Volcanic Province (DVP). A layered crustal model with irregular interfaces of small amplitude has been used for elastostatic stress calculations. The computed principal stress differences show a significant concentration at 5–20 km depths beneath the western side of the region. The maximum magnitude of principal stress difference occurs beneath the Karad at a depth of 10 km with a value of 60 MPa. The deviatoric stress estimates are further superposed on inferred stresses due to the regional plate tectonic forces. These results show principal stress difference concentrations beneath the Koyna, Poona and Karad regions which may thus be more vulnerable to brittle failure. It is also seen that the principal total stress directions point to the strike slip motion at Koyna, similar to that which is associated with the 1967 Koyna earthquake.

• Stability of vegetation growth in a noise-induced system

Vegetation community plays a pivotal role in various geomorphic processes. The growth of vegetation intrinsically depends on the effective shear stresses exerted by the flow of material (e.g., water or soil) along the slope. We comparatively assess the growth and decay of vegetation using linear and logistic growth model coupled with a runoff erosion model. The linear growth model predicts a sharp decrease in the non-dimensional vegetation profile from the upper reach to the lower part along the slope. However, the logistic growth model delivers a smooth gradual decrease in the vegetation extent. Additionally, we propose a stochastic model to capture the role of internal and external factors in the dynamics of vegetation growth using two Gaussian noises. The steady probability distribution functions from the stochastic model provide insights about the role of different noises on the reaction of the system and suggest that bio-environmental factors are difficult to segregate from one another.

$\bf{Highlights}$

$\bullet$ Comparative study between logistic and linear vegetation growth model coupled with a surface erosion model.

$\bullet$ Steady-state equilibrium vegetation profile along any slope suggests that the logistic growth model is more realistic.

$\bullet$ Effect of Gaussian noises in vegetation growth has been demonstrated with the aid of stationary probability distribution.

• # Journal of Earth System Science

Volume 132, 2023
All articles
Continuous Article Publishing mode

• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019

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