Vikas Rock - Profile on Academia.edu (original) (raw)

Papers by Vikas Rock

International Journal of Solids and Structures, 2008

The knowledge of shear resistance in earth faults is of fundamental importance to our understandi... more The knowledge of shear resistance in earth faults is of fundamental importance to our understanding of the magnitude of stress drop and the associated energy release during typical seismic rupture events. In the present study a modified torsional Kolsky bar is employed to investigate frictional slip resistance in rock-analog materials (i.e., quartz and soda lime glass) at normal stresses of relevance to earthquake physics (30-80 MPa) and co-seismic slip rates. The results indicate the coefficient of kinetic friction to be in the range of 0.2 to 0.3. These values of the coefficient of friction are much lower when compared to those obtained in rocks at quasi-static slip rates. In all experiments slip weakening is observed and is preceded by slip strengthening. The slip weakening is understood to be due to thermal weakening induced by flash-heating at asperity contacts and requires a few mm of slip to be effective; the slip strengthening is understood to be due to an increase in the real area of contact at the asperity junctions due to localized plastic flow and subsequent coalescence and solidification of local softened/melt patches at the slip interface.

Applied Geochemistry, 2005

India has an increasing incidence of fluorosis, dental and skeletal, with some 62 million people ... more India has an increasing incidence of fluorosis, dental and skeletal, with some 62 million people at risk. High fluoride groundwaters are present especially in the hard rock areas south of the Ganges valley and in the arid north-western part of the country. The phenomenon is related to groundwater with residual alkalinity ðCa 2þ < HCO À 3 Þ. Fluoride concentrations are governed by adsorption equilibria and by fluorite solubility. Evapotranspiration leads to a precipitation of calcite, a lowering of Ca activity and increase in Na/Ca ratios, and this allows an increase in F À levels. In southern India, Mg seems to be controlled by dolomite, while sepiolite and palygorskite are Mg sinks in Rajasthan but may then release F À under alkaline conditions. The latter two minerals are probably also important sources and sinks for F À in the hydroxy-positions. The increase in the extent of sodic soils as a result of irrigation is a contributing factor to the increasing incidence of fluorosis. Remedial measures including addition of gypsum and rainwater harvesting are needed even in areas where the sodicity does not cause structural problems in the soil.

Journal of Geophysical Research, 2011

1] The origin of pulverized rocks (PR) in surface outcrops adjacent to the fault cores of the San... more 1] The origin of pulverized rocks (PR) in surface outcrops adjacent to the fault cores of the San Andreas and other major faults in Southern California is not clear, but their structural context indicates that they are clearly associated with faulting. An understanding of their origin might allow inferences to be drawn about the nature of dynamic slip on faults, including rupture mechanisms and their speed during earthquakes. In the present study, we use split Hopkinson bar recovery experiments to investigate whether PR can be produced under dynamic stress wave loading conditions in the laboratory and whether PR is diagnostic of any particular process of formation. The results of the study indicate that in Westerly granite for transition from sparse fracture to pervasive pulverization requires high strain rates in excess of 250/s and that the formation of PR may be inhibited at the larger burial depths. The constraint imposed by field observations of the relatively low strains (1-3%) in PR recovered from the field and the laboratory derived threshold for the critical strain rate (∼250/s and higher) together indicate that a dynamic supershear-type rupture may be necessary for the origin of pulverized rocks at distances of tens of meters away from the fault plane as observed in the field for both large strike-slip-type and the relatively small dip-slip-type fault ruptures in nature.

Lithology and Mineral Resources, 2001

A close relation of the organic carbon (Corg) content with major has been established for rocks o... more A close relation of the organic carbon (Corg) content with major has been established for rocks of the Upper Jurassic–Lower Cretaceous Bazhenov Formation. Applying the method of multiple linear regression, it has been demonstrated that the Corgcontent in rocks of the Bazhenov Formation is stringently controlled by its bulk chemical composition. This inference is consistent with the existing ideas regarding a close interrelation between the following main components of rocks: organic carbon and authigenic quartz formed on remains of Radiolaria; pyrite formed in a highly reducing medium of Corg-rich sediments; and terrigenous clayey material diluting the authigenic siliceous–carbonaceous–pyritic matrix. These components chiefly determine the spectrum of major elements in the Bazhenov Formation. The establishment of the close relation between the Corgcontent and the group of major elements refutes the suggestion of some authors that siliceous material was supplied to nonlithified sediments of the Bazhenov sea by hydrothermal solutions, because this mechanism would have inevitably upset geochemical relations between elements in the studied rocks.

Canadian Journal of Microbiology, 2005

Enterobacter asburiae PSI3 is a rhizospheric isolate that solubilizes mineral phosphates by the a... more Enterobacter asburiae PSI3 is a rhizospheric isolate that solubilizes mineral phosphates by the action of a phosphate starvation-inducible GDH (EC 1.1.5.2). We report here that GDH activity of this isolate shows broad substrate range, being able to act on mono and disaccharides. Enterobacter asburiae PSI3 was proficient at bringing about a drop in pH and solubilization of RP with the use of 75 mmol/L of each of the GDH substrate sugars tested as the sole C source. It liberated amounts of P ranging from 450 µmol/L (on arabinose) to 890 µmol/L (on glucose). When grown on a mixture of 7 GDH substrates at concentrations of 15 mmol/L each, the bacterium solubilized RP equivalent to 46% of the value when 75 mmol glucose/L was the C source. HPLC analysis of the culture supernatant under these conditions showed that the acidification of the media is primarily due to the production of organic acids. The significance of these results on the efficacy of E. asburiae PSI3 at solubilizing phosphates under rhizospheric conditions is discussed.

$Research paper thumbnail of Delineation of groundwater-bearing fracture zones in a hard rock area integrating very low frequency electromagnetic and resistivity data$

Journal of Applied Geophysics, 2005

Integrated electrical and electromagnetic surveys were carried out in hard rock areas of Purulia ... more Integrated electrical and electromagnetic surveys were carried out in hard rock areas of Purulia district (West Bengal), India, for delineation of groundwater-bearing zones that would be suitable for construction of deep tube-wells for large amounts of water. Groundwater movement that occurs through fractures in hard rocks is suitable to be delineated by very low frequency (VLF) electromagnetic surveys. A detailed survey of the area was done using a VLF-WADI instrument and appropriate locations were selected for further study using Schlumberger resistivity sounding. Hence, the entire area was surveyed in a relatively short time by the combined use of resistivity and electromagnetic surveys.