Variations in shear wave velocity and soil site class in Kolkata city using regression and sensitivity analysis

The detrimental effects of an earthquake are strongly influenced by the response of soils subjected to dynamic loading. The behavior of soils under dynamic loading is governed by the dynamic soil properties such as shear wave velocity, damping characteristics and shear modulus. Worldwide, it is a common practice to obtain shear wave velocity (V _s in m/s) using the correlation with field standard penetration test (SPT) N values in the absence of sophisticated dynamic field test data. In this paper, a similar but modified advanced approach has been proposed for a major metro city of eastern India, i.e., Kolkata city (latitudes 22°20′N–23°00′N and longitudes 88°04′E–88°33′E), to obtain shear wave velocity profile and soil site classification using regression and sensitivity analyses. Extensive geotechnical borehole data from 434 boreholes located across 75 sites in the city area of 185 km² and laboratory test data providing information on the thickness of subsoil strata, SPT N values, consistency indices and percentage of fines are collected and analyzed thoroughly. A correlation between shear wave velocity (V _s) and SPT N value for various soil profiles of Kolkata city has been established by using power model of nonlinear regression analysis and compared with existing correlations for other Indian cities. The present correlations, having regression coefficients (R ²) in excess of 0.96, indicated good prediction capability. Sensitivity analysis predicts that significant influence of soil type exists in determining V _s values, for example, typical silty sand shows 30.4 % increase in magnitude of V _s as compared to silt of Kolkata city. Moreover, the soil site classification shows Class D and Class E category of soil that exists typically in Kolkata city as per NEHRP (Recommended provisions for seismic regulations for new buildings and other structures—Part 1: Provisions. Prepared by the Building Seismic Safety Council for the Federal Emergency Management Agency (Report FEMA 450), Washington, DC, 2003) guidelines and thereby highlighting the seismic vulnerability of the city. The results presented in this study can be utilized for seismic microzonation, ground response analysis and hazard assessment for Kolkata city.

     

Extension of the Kepler problem towards minimization of energy and gravity softening

The classical Kepler Problem consists in the determination of the relative orbital motion of a secondary body (planet) with respect to the primary body (Sun), for a given time. However, any natural system tends to have minimum energy and is subjected to differential gravitational or tidal forces (called into play mainly due to the finite size and deformability of the secondary body). We formulate the Kepler Problem taking into account the finite size of the secondary body and consider an approximation which tends towards minimum energy orbits, by increasing the dimensionality of the problem. This formulation leads to a conceivable natural explanation of the fact that the planetary orbits are characterized by small eccentricities.     

An analysis of precipitation climatology over Indian urban agglomeration

Theoretical and Applied Climatology - While urban areas in India are rapidly expanding, the analysis of how the precipitation regimes are changing is very limited. In the present study, an attempt...     

Mobility of arsenic in West Bengal aquifers conducting low and high groundwater arsenic. Part I: Comparative hydrochemical and hydrogeological characteristics

The present study demonstrates the importance of hydrogeochemical characteristics (groundwater flow and recharge) of an aquifer in the release of As to groundwater. The study area (∼20 km²) is located in Chakdaha block, Nadia district, West Bengal, which hosts groundwaters of variable As content. The spatial distribution pattern of As is patchy with areas containing groundwater that is high in As (>200 μg L⁻¹) found in close vicinity to low As (<50 μg L⁻¹) groundwaters (within 100 m). The concentration of groundwater As is found to decrease with depth. In addition, the data shows that there is no conspicuous relationship between high groundwater As concentration and high groundwater abstraction, although the central cone of depression has enlarged over 2 a and is extending towards the SE of the study area. The river Hooghly, which forms the NW boundary of the study site, shows dual behaviour (effluent and influent during pre- and post-monsoon periods, respectively), complicating the site hydrogeology. The observed groundwater flow lines tend to be deflected away from the high As portion of the aquifer, indicating that groundwater movement is very sluggish in the As-rich area. This leads to a high residence time for this groundwater package, prolonging sediment–water interaction, and hence facilitating groundwater As release.     

Economic significance of colonial invasions in Khejuri-Hijli coastal sector of Purba Medinipur district,West Bengal: A geographical review

Khejuri- Hijili coastal area, now extends over the Khejuri police station, is situated in the southeastern part of the district of Purba Medinipur of West Bengal, on the western bank of the Hugli river. Between 21°47'42"N-22°4'N latitudes and 87°45'4"E-88°18"E longitudes the area covers about 267.97 sq. km. At the confluence of the rivers Bhagirathi-Hugli and the Bay of Bengal, Hijili emerged as an island from the estuarine surroundings around 1400-1500 A.D. afterward the island became covered with natural mangroves. Gradually it became the abode of fishermen. To gather some primary data, household survey by different questionnaire, topographic survey was done. Secondary data are mainly produced by assembling historical charts, maps, literatures for the specified work of the area concerned. Historical records including documents, survey notes, maps and photographs provided valuable information about the study area. Remains of early structures, monuments, and office buildings have been vigilantly watched and written reports and research articles have been carefully studied for sequencing the socio-economic history of the area. Later on accuracy assessment was performed by comparing two sources of information: classification of map derived from old records and maps and the ground truth information. The output obtained by performing the above steps includes land use and other maps and charts. These outputs were then analyzed to detect the historical significance of Khejuri-Hijili sector of the Hugli estuary and its sequential deterioration. These changes in the study area that were identified from classified maps, charts and diagram were tabulated.     

Tidal disruption of a disk galaxy

The tidal force effects of a spherical galaxy passing head-on through a disk galaxy have been studied for various orientations of the disk galaxy with respect to the direction of relative motion of the two galaxies. The density distribution of the spherical galaxy is taken to be that of a polytrope of indexn=4 and that of the disk galaxy is taken to be, (r)=_ce^–4r/R, where _c is the central density andR the radius of the disk. It is found that the disruptive effects due to the tidal force are minimum when the plane of the disk lies along the direction of relative motion, but are maximum when the plane of the disk is slightly inclined to this direction (about 15°). The tidal force effects at the median radius have also been computed. The tadal force effects are much higher in the interior region of the disk.     

A hydro-structural analysis program for TLPS

The TLP configuration in this paper comes from the case study of the ISSC Derived Loads Committee I.2 in 1985. Two models, Model 1 and Model 2, are created aiming at developing a computational tool to handle hydro-dynamic and structural aspects together to help the TLP designer. Another objective is to generate relevant information for a non-linear static local stress analysis of TLP components from a dynamic hydro-structural global analysis. Model 2 is developed for LUSAS, a general purpose, well established, FE software, to validate the in-house program DCATLP. Model 1 and Model 2 are purposely made slightly different in the tether modelling so that the non-linear formulations in DCATLP to treat a TLP as a coupled system with the hull and tethers can be verified with a straightforward linear step-by-step dynamic analysis in LUSAS. The code in DCATLP has advanced features to account for some complex aspects of TLPs, such as compliant characteristics. The results from DCATLP can be directly used in the reliability based structural design of TLP components and subsequent optimisation studies.     

Chemical and isotopic composition of the lower crust beneath the Meguma Lithotectonic Zone,Nova Scotia: evidence from granulite facies xenoliths

Granulite-facies xenoliths from an Upper Devonian lamprophyre dyke near Tangier, Nova Scotia, provide new information about the lower crust in the Meguma Zone. Two mineralogically and chemically distinet groups of xenoliths occur. Both groups contain quartz+feldspar+biotite+Fe–Ti oxides+sulfides. In addition, group A contains garnet+graphite±[aluminosilicates+spinel±sapphirine (hight Al₂O₃ subgroups A1 and A2)] or [clinopyroxene+sphene+apatite (high CaO sub-group A3)]. Group B has highly variable proportions of orthopyroxene (B1), clinopyroxene (B2), and amphibole (B3). Trace-element contents of the highly aluminous xenoliths compare closely with average to upper crustal model compositions and are similar in many aspects to other undepleted granulite-facies rocks. LowP-T sedimentary assemblages of quartz-chlorite-clay minerals-calcite-albite or paragonite can account for the compositions of group A xenoliths. Within group B, a high-MgO (MgO>13 wt%) subgroup with high transition-metal contents, and low-MgO (MgO<9 wt%) sub-groups with higher LIL (large-ion-lithophile) element contents exist. Although the rare-earth and high-field-strength elements indicate a tholeiitic or low-K calc-alkaline chemistry, the LIL elements are as high as those from high-K calc-alkaline volcanic are rocks. Isotopically, group A ranges from Nd_t=-2.56 to-0.80 and⁸⁷Sr/⁸⁶Sr _t =0.7046 to 0.7182 fort=370 Ma. For group B these values are +1.45 to +5.33 and 0.7028 to 0.7048, respectively. Model ages (T_CHUR) are correspondingly low and are tightly constrained (544±52 Ma). These young ages contrast with the middle Proterozoic Nd model ages of the overlying Meguma Zone low-grade flysch. This time-inverted stratigraphy appears to be the product of a tectonic break between a younger autochthonous Tangier lower crust (Avalon), and an older allochthonous Meguma Group upper crust.