Revisiting the Koyna-Warna seismic zone: strain budget,present-day potential and associated hazard

Journal of Seismology - The Koyna-Warna region in western India is well known around the globe for recurrent reservoir-triggered seismicity soon after the impoundment of the Koyna and Warna...     

Primary sedimentary structures and MISS in Gulcheru quartzite along SW part of Cuddapah basin

Sedimentary structures are very useful in paleocurrent analysis and interpretation of siliciclastic shallow marine environment. These interesting sedimentary structures such as parallel bedding, cross bedding, ripples, and mud cracks as well as synaeresis cracks, are best studied in the field. They are formed by a variety of sedimentary processes, including fluid flow, sediment-gravity flow, soft-sediment deformation and biogenic activity. Gulcheru Formation has evidence of interaction of microbial communities with clastic sedimentation during Palaeoproterozoic time. Because of high porosity-permeability of siliciclastics of Gulcheru Formation, palaeontologists do not expect many fossils preserved in such rocks and thus they have been overlooked. Microbially induced sedimentary structures (MISS) are highlighted in the Gulcheru Formation. They are indicative of shallow marine environment. Gulcheru Formation shows alluvial fan to shallow marine shelf environments within a limited thickness of about ~ 110m, which indicates an alluvial plain coast where alluvial deposits are modified by wave forces.     

An approach of understanding acid volcanics and tuffaceous volcaniclastics from field studies: A case from Tadpatri Formation,Proterozoic Cuddapah basin,Andhra Pradesh,India

The lower stratigraphic part of the Cuddapah basin is marked by mafic and felsic volcanism. Tadpatri Formation consists of a greater variety of rock types due to bimodal volcanism in the upper part. Presence of bimodal volcanism is an indication of continental rift setting. Various genetic processes involved in the formation of such volcanic sequence result in original textures which are classified into volcaniclastic and coherent categories. Detailed and systematic field works in Tadpatri–Tonduru transect of SW Cuddapah basin have provided information on the physical processes producing this diversity of rock types. Felsic volcanism is manifested here with features as finger print of past rhyolite-dacite eruptions. Acid volcanics, tuffs and associated shale of Tadpatri Formation are studied and mapped in the field. With supporting subordinate studies on geochemistry, mineralogy and petrogenesis of the volcanics to validate field features accurately, it is understood that volcanism was associated with rifting and shallow marine environmental condition. Four facies (i.e., surge, flow, fall and resedimented volcaniclastic) are demarcated to describe stratigraphic units and volcanic history of the mapped area. The present contribution focuses on the fundamental characterization and categorization of field-based features diagnostic of silica-rich volcanic activities in the Tadpatri Formation.     

A Cautionary Note on the Use of Monin–Obukhov Similarity Theory in Very High-Resolution Large-Eddy Simulations

In several recent large-eddy simulation studies, the lowest grid level was located well within the roughness sublayer. Monin–Obukhov similarity-based boundary conditions cannot be used under this scenario, and in this note we elaborate on this fundamental problem and suggest potential solutions.     

Thermal conductivity of Higher Himalayan Crystallines from Garhwal Himalaya, India

We report the measurements of thermal conductivity for some Higher Himalayan Crystalline rocks from Joshimath and Uttarkashi areas of the Garhwal Himalaya. Seventy-three rock samples including gneiss, metabasic rock and quartzite were measured. Gneissic rocks, which include augen gneiss, banded gneiss, felsic gneiss and fine-grained gneiss, exhibit a wide range in conductivity, from 1.5 to 3.6 Wm^− 1K^− 1 for individual samples, and 2.1 to 2.7 Wm^− 1K^− 1 for the means. Among these, augen gneisses and banded gneisses show the largest variability. Of all the rock types, quartzites (mean 5.4 Wm^− 1K^− 1) and metabasic rocks (mean 2.1 Wm^− 1K^− 1) represent the highest and lowest mean values respectively. The range in conductivity observed for gneissic rocks is significantly higher than that generally found in similar rock types in cratonic areas. The rock samples have very low porosity and exhibit feeble anisotropy, indicating that they do not contribute to the variability in thermal conductivity. Besides variations in mineralogical composition, the heterogeneous banding as well as intercalations with metabasic rocks and quartz veins, a common occurrence in structurally complex areas, appears to cause the variability in conductivity. The study therefore brings out the need for systematic characterization of thermophysical properties of major rock types comprising the Himalayan region for lithospheric thermal modeling, assessment of geothermal energy and geo-engineering applications in an area. The dataset constitutes the first systematic measurements on the Higher Himalayan Crystalline rocks.     

Geothermal investigations in the Upper Vindhyan sedimentary rocks of Shivpuri area,central India

Heat flow has been determined by combining temperature measurements in 7 boreholes with thermal conductivity measurements in the Upper Vindhyan sedimentary rocks of Shivpuri area, central India. The boreholes are distributed at 5 sites within an area of 15 × 10 km²; their depths range from 174 to 268 m. Geothermal gradients estimated from borehole temperature profiles vary from 8.0–12.7 mK m⁻¹ in the sandstone-rich formations to 25.5–27.5 mK m⁻¹ in the shale-rich formations, consistent with the contrast in thermal conductivities of the two rock types. Heat flow in the area ranges between 45 and 61 mW m⁻², with a mean of 52±6 mW m⁻². The heat flow values are similar to the >50 mW m⁻² heat flow observed in other parts of the northern Indian shield. The heat flow determinations represent the steady-state heat flow because, the thermal transients associated with the initial rifting, convergence and sedimentation in the basin as well as the more recent Deccan volcanism that affected the region to the south of the basin would have decayed, and therefore, the heat flow is in equilibrium with the radiogenic heat production of the crust and the heat flow from the mantle. The present study reports the heat flow measurements from the western part of the Vindhyan basin and provides heat flow information for the Bundhelkhand craton for the first time. Radioelement (Th, U and K) abundances have been measured both in the sedimentary rocks exposed in the area as well as in the underlying basement granite-gneiss of Bundelkhand massif exposed in the adjacent area. Radioactive heat production, estimated from those abundances, indicate mean values of 0.3 μW m⁻³ for sandstone with inter-bands of shale and siltstone, 0.25 μW m⁻³ for sandstone with inter-bands siltstone, 0.6 μW m⁻³ for quartzose sandstone, and 2.7 μW m⁻³ for the basement granitoids. With a total sedimentary thickness not exceeding a few hundred metres in the area, the heat production of the sedimentary cover would be insignificant. The radioactive heat contribution from the basement granitoids in the upper crust is expected to be large, and together with the heat flow component from the mantle, would control the crustal thermal structure in the region.     

A CCD photometric study of the late type contact binary EK Comae Berenices

We present CCD photometric observations of the W UMa type contact binary EK Comae Berenices using the 2 m telescope of IUCAA Girawali Observatory, India. The star was classified as a W UMa type binary of subtype-W by Samec et al. (1996). The new V band photometric observations of the star reveal that shape of the light curve has changed significantly from the one observed by Samec et al. (1996). A detailed analysis of the light curve obtained from the high-precision CCD photometric observations of the star indicates that EK Comae Berenices is not a W-type but an A-type totally eclipsing W UMa contact binary. The photometric mass ratio is determined to be 0.349 ± 0.005. A temperature difference of ΔT = 141 ± 10 K between the components and an orbital inclination of i[°] = 89.800 ± 0.075 were obtained for the binary system. Absolute values of masses, radii and luminosities are estimated by means of the standard mass-luminosity relation for zero age main-sequence stars. The star shows O’Connell effect, asymmetries in the light curve shape around the primary and secondary maximum. The observed O’Connell effect is explained by the presence of a hot spot on the primary component.     

Solving the graceful exit problem in superstring cosmology

We briefly review the status of the “graceful exit” problem in superstring cosmology and present a possible resolution. It is shown that there exists a solution to this problem in two-dimensional dilaton gravity provided quantum corrections are incorporated. This is similar to the recently proposed solution of Rey. However, unlike in his case, in our one-loop corrected model the graceful exit problem is solved for any finite number of massless scalar matter fields present in the theory.