Spherical shock wave propagation in self-gravitating stars

The problem of shock wave propagation in a heat-conducting and self-gravitating medium has been studied. The shock is strong enough so that the ambient gas pressure can be neglected. The variation of velocity, density, temperature, and mass distributions behind the shock have been obtained from a numerical solution of similarity equations involved.     

Seismic Hazard Mapping and Microzonation in the Sikkim Himalaya through GIS Integration of Site Effects and Strong Ground Motion Attributes

The seismic ground motion hazard is mapped in the Sikkim Himalaya with local and regional site conditions incorporated through geographic information system. A strong motion network in Sikkim comprising of 9 digital accelerographs recorded more than 100 events during 1998–2002, of which 41 events are selected with signal-to-noise ratio 3 for the estimation of site response (SR), peak ground acceleration (PGA) and predominant frequency (PF) at all stations. With these and inputs from IRS-1C LISS III digital data, topo-sheets, geographical boundary of the State of Sikkim, surface geological maps, soil taxonomy map in 1:50,000 scale and seismic refraction profiles, the seismological and geological thematic maps, namely, SR, PGA, PF, lithology, soil class, %slope, drainage, and landslide layers are generated. The geological themes are united to form the basic site condition coverage of the region. The seismological themes are assigned normalized weights and feature ranks following a pair-wise comparison hierarchical approach and later integrated to evolve the seismic hazard map. When geological and seismological layers are integrated together through GIS, microzonation map is prepared. The overall site response, PGA and predominant frequency show an increasing trend in the NW–SE direction peaking at Singtam in the lesser Himalaya. As Main Boundary Thrust (MBT) is approached, the attribute value increases further. A quasi-probabilistic seismic hazard index has been proposed based on site response, peak ground acceleration and predominant frequency. Six seismic hazard zones are marked with percent probability <22%, 22–37%, 37–52%, 52–67%, 67–82%, >82% at 3 Hz and <20%, 20–34%, 34–48%, 48–61%, 61–75%, >75% at 9 Hz. In the microzonation vector layer of integrated seismological and geological themes also six major zones are mapped, with percent probability <15%, 15–31%, 31–47%, 47–63%, 63–78%, >78% at low frequency end. The maximum risk is attached to the probability greater than 78% in the Singtam and its adjoining area. These maps are generally better spatial representation of seismic hazard including site-specific analysis.     

Propagation of spherical MHD shock-waves in self-gravitating gas

A theoretical model of shock-wave propagation has been studied in a heat-conducting and a self-gravitating medium. The effects of magnetic field has been taken into consideration. The shock is strong enough to neglect the ambient gas pressure. The variation of flow variables behind the shock have been investigated numerically.     

The analysis of composite structures with prescribed frictional conditions at the interfaces

A method is presented for the analysis of composite structures with prescribed frictional conditions at the interfaces. The method, which can also be used for the piecewise solution of large structures, is illustrated by analyzing a test problem with two interfaces.     

Neotectonic activity of the Bomdila Fault in northeastern India from geomorphological evidences using remote sensing and GIS

One of the major geological structures across the Brahmaputra valley, which stretches from the Eastern Himalayas up to the Naga Hills, is the Bomdila Fault. Parts of the courses of the rivers – the Brahmaputra, Dhansiri (south-S), Bargang and many others – are aligned along this structure. The influence of this structure on the courses of these rivers has been studied in detail using topographic maps, satellite data and field evidences. The signatures obtained such as: (a) an unusually linear course of the lower part of the Dhansiri (S) river from Golaghat up to Dhansirimukh, (b) the abandonment of the westerly course of the earlier Dhansiri (S) river (flowing through Kaziranga) towards the present NW direction by avulsion, (c) knick bends in the MBT–MCT and Naga Thrust of Belt of Schuppen, (d) a linear 15 m high topographic scarp on the left bank of the Dhansiri (S) near Numaligarh and (e) an anomalous SE–NW trending course of the Brahmaputra from Dhansirimukh up to Hartamuli along with the parts of the rivers Buroi and Bargang on the north in the same trend infers the influence of a fault-type structure. Since all these linear segments of the rivers align along the NW–SE trending Bomdila Fault, it infers the influence of the later on the courses of these rivers. The neotectonic activity along this fault might have caused the linear high scarp and abandonment of earlier river courses.     

Planetary wave reflection and its impact on tropospheric cold weather over Asia during January 2008

Reflection of stratospheric planetary waves and its impact on tropospheric cold weather over Asia during January 2008 were investigated by applying two dimensional Eliassen-Palm （EP） flux and three-dimensional Plumb wave activity fluxes.The planetary wave propagation can clearly be seen in the longitude-height and latitude-height sections of the Plumb wave activity flux and EP flux,respectively,when the stratospheric basic state is partially reflective.Primarily,a wave packet emanating from Baffin Island/coast of Labrador propagated eastward,equatorward and was reflected over Central Eurasia and parts of China,which in turn triggered the advection of cold wind from the northern part of the boreal forest regions and Siberia to the subtropics.The wide region of Central Eurasia and China experienced extreme cold weather during the second ten days of January 2008,whereas the extraordinary persistence of the event might have occurred due to an anomalous blocking high in the Urals-Siberia region.     

Geochemical characteristics of the mud volcano fluids in southwestern Taiwan and their possible linkage to elevated arsenic concentration in Chianan plain groundwater

Fluid and mud samples were collected from Wushanting (WST), Hsiaokunshui (HKS), Yenshuikeng (YSK), Kuantzeling (KZL), and Kunshuiping (KSP) mud volcanoes of southwestern Taiwan. Concentrations of major ions and trace elements in mud volcanic fluids were analyzed to find the possible linkage to elevated arsenic (As) concentrations in the Chianan plain groundwater. The elevated Na⁺, K⁺, and Cl⁻ concentrations indicated possible marine origin of the fluids. The trace element concentrations in the mud volcanic fluids were generally low, but the As concentrations were up to 0.12 mg/L. High contents of As, Fe, and Mn were observed in the mud samples. Saturation index calculations indicated that both carbonate and oxide minerals acted as potential sinks for As in the mud volcanic fluids. Arsenic in the dewatering fluids and muds may be transported by the subsurface flow and surface streams as suspended solids and eventually deposited in the Chianan plain aquifers. Under reducing conditions, As may be released from the host minerals (such as Fe- and Mn-oxides/hydroxides), thereby causing widespread groundwater As pollution.     

Alterations in Geochemical Associations in Artificially Disturbed Deep-Sea Sediments

In view of the role of Sediment geochemistry in regulating the benthic ecosystem, diagenetic remobilization of dissolved constituents, bottom water redox, and regeneration of benthic fluxes, surficial sediments in and around the track disturbed by a “benthic disturber” were studied for metal variation in three phases: (1) before the disturbance, (2) immediately after the disturbance, and (3) during monitoring of restoration after ~44 months, from the same locations. Minor variations in metal concentrations before the disturbance ere noticed indicating the homogeneity in the area or supply from similar source areas. Terrigenous fraction determined normatively from titanium contents in these sediments ranges between 40 and 47%. Most of the elements analyzed showed reduced average concentrations immediately after the disturbance suggesting physical removal and resedimentation in other areas with the migration of the plume. All the elements showed positive relation and coherence in the sediments collected after the disturbance, irrespective of their susceptibility to changes in provenance and depositional environment, whereas elemental associations during the predisturbance and monitoring periods can be explained by the known geochemical processes. The changes in Al, Ti, excess aluminium contents, their interelement relations, and factor analyses, suggest the possible transformation of clay mineral type due to the benthic disturbance that would involve changes in surface chemistry of clays. Interelement relations among redox-sensitive elements have also changed with time. This includes decoupling of Co from Mn after 44 months, probably due to the varying oxidation kinetics of two major oxides, Fe and Mn. Model calculations suggest increased diagenetic remobilization rates of Mn during the monitoring phase. Substantial increase in redox-sensitive elements, especially Fe and Mn indicate oxygenation of bottom water due either to reduced activity of benthic burrowing organisms or to renewal of oxygen-rich Antarctic Bottom water (AABW). Increase in these elements is consistent with the results of the HEBBLE experiment, where the burrows seem to protect these elements from strong bottom currents. Restoration of predisturbance values in the terrigenous component is attributed to the influence of shifts in the direction of bottom flow and suggests that bottom currents would play a major role in restoring the lithogenic component by transporting it from other locations within the Basin during commercial mining operations.     

Cyclic sedimentation of the Barren Measures Formation (Damuda Group), Talchir Gondwana basin: Statistical appraisal from borehole logs

The succession of lithofacies of a part of the Barren Measures Formation of the Talchir Gondwana basin has been studied by statistical techniques. The lithologies have been grouped under five facies states viz coarse-, medium-, and fine-grained sandstones, shale and coal for statistical analyses. Markov chain analysis indicates the arrangement of Barren Measures lithofacies in the form of fining upward cycles. A complete cycle consists of conglomerate or coarse-grained sandstone at the base sequentially succeeded by medium-and fine-grained sandstones, shales and coal at the top. The entropy analysis puts the Barren Measures cycles into A-4 type cyclicity, which consists of different proportions of lower, upper and side truncated cycles of lithologic states. Regression analysis indicates a sympathetic relationship between total thickness of strata (net subsidence) and number of cycles and an antipathic relationship between average thickness and number of sedimentary cycles. The cyclic sedimentation of the Barren Measures Formation was controlled by autocyclic process which occurred due to the lateral migration of streams triggered by intrabasinal differential subsidence. In many instances, the clastic sediments from the laterally migrating rivers interrupted the cyclic sedimentation resulting in thinner cycles in areas where the number of cycles are more. Principal component and multivariate regression analyses suggest that the net subsidence of the basin is mostly controlled by the thickness of sandstones, shale beds and coal stringers.     

Relationship between Net Subsidence and Coal Cycle Parameters—A Statistical Appraisal from Subsurface Logs of Damuda Group,Talchir Gondwana Basin,India

Total thickness of strata and coal cycle parameters of the three formations, i.e. Karharbari, Barakar, and Barren Measures of the Damuda Group of the Talchir Gondwana basin were subjected to bivariate and multivariate statistical analyses. Polynomial regression lines were fitted to data sets consisting of total thickness of strata, number of coal cycles, and average thickness of coal cycles of the three formations of the Damuda Group. A significant direct relationship is observed between total thickness (net subsidence) of strata and number of coal cycles, while a significant inverse relationship exists between the number of coal cycles and their average thickness. Principal component and multiple regression analyses suggest that lithological parameters of the coal bearing strata reflect the dynamic of the basin subsidence. The sedimentary distributive mechanism in the form of lateral migration of streams or drainage diversion caused in response to differential subsidence of the depositional surface seem to be appropriate mechanisms for the development of coal cycles and peat swamps in the Talchir basin. Often during Karharbari sedimentation, peat accumulated in abandoned channels was scoured away by high energy migrating channels. On the other hand, Barakar peat swamps developed in a distal part of the flood plain, as a result of which many of the coal seams could be of appreciable thickness. The advent of arid climatic condition retarded the growth of vegetation to a larger extent that prevented profuse development of coal seams during the Barren Measures Formation.