On the propagation of disturbances in a composite viscoelastic layer in a magnetic field     

Sukumar Basu Mallik 《Pure and Applied Geophysics》1972,96(1):52-60

Summary The propagation of disturbances in a composite viscoelastic layer when subjected to an impulsive force in the presence of a primary magnetic field, has been investigated in this note. The mechanical displacement has been derived from the electro-magnetic equations of Maxwell, the equation of motion and the stress-strain relations of the materials considered and has been computed for small values of time.  相似文献   

Mobility of arsenic in West Bengal aquifers conducting low and high groundwater arsenic. Part II: Comparative geochemical profile and leaching study     

Bibhash Nath  Zsolt Berner  Debashis Chatterjee  Sukumar Basu Mallik  Doris Stüben 《Applied Geochemistry》2008

Aquifer sediments from areas of low- and high-As groundwater were characterized mineralogically and geochemically at a field site in the Nadia district of West Bengal, India. Leaching experiments and selective extraction of the sediments were also carried out to understand the release mechanism of As in the sub-surface. The correlation between measured elements (major, minor and trace) from low- and high-As groundwater areas are only significant for As, Fe and Mn. The borehole lithology and percentage of silt and clay fraction demonstrates the dominance of finer sediments in the high-As aquifer. Multivariate analysis of the geochemical parameters showed the presence of four different mineral phases (heavy-mineral fraction, phyllosilicates/biotite/Fe-oxyhydroxides, carbonates and sulphides) in the sediments. Selective extraction of sediment reveals that amorphous Fe-oxyhydroxide acts as a potential sink for As in the sub-surface. The result is consistent with microbially mediated redox reactions, which are controlled in part by the presence of natural organic matter within the aquifer sediments. The occurrences of As-bearing redox traps, primarily formed of Fe- and Mn-oxides/hydroxides, are also important factors that control the release of As into groundwater at the study site.  相似文献   

Impact of climate on tea production: a study of the Dooars region in India     

Mallik  Piyashee  Ghosh  Tuhin 《Theoretical and Applied Climatology》2022,147(1-2):559-573

Theoretical and Applied Climatology - The Dooars region of West Bengal in India is a major tea producing region that contributes around 25% of the national tea yield. Changes in weather patterns...  相似文献   

Paleocene on-spreading-axis hotspot volcanism along the Ninetyeast Ridge: An interaction between the Kerguelen hotspot and the Wharton spreading center     

K. S. Krishna  D. Gopala Rao  L. V. Subba Raju  A. K. Chaubey  V. S. Shcherbakov  A. I. Pilipenko  I. V. Radhakrishna Murthy 《Journal of Earth System Science》1999,108(4):255-267

Investigations of three plausible tectonic settings of the Kerguelen hotspot relative to the Wharton spreading center evoke the on-spreading-axis hotspot volcanism of Paleocene (60-54 Ma) age along the Ninetyeast Ridge. The hypothesis is consistent with magnetic lineations and abandoned spreading centers of the eastern Indian Ocean and seismic structure and radiometric dates of the Ninetyeast Ridge. Furthermore, it is supported by the occurrence of oceanic andesites at Deep Sea Drilling Project (DSDP) Site 214, isotopically heterogeneous basalts at Ocean Drilling Program (ODP) Site 757 of approximately the same age (59-58 Ma) at both sites. Intermix basalts generated by plume-mid-ocean ridge (MOR) interaction, exist between 11° and 17°S along the Ninetyeast Ridge. A comparison of age profile along the Ninetyeast Ridge between ODP Sites 758 (82 Ma) and 756 (43 Ma) with similarly aged oceanic crust in the Central Indian Basin and Wharton Basin reveals the existence of extra oceanic crust spanning 11° latitude beneath the Ninetyeast Ridge. The extra crust is attributed to the transfer of lithospheric blocks from the Antarctic plate to the Indian plate through a series of southward ridge jumps at about 65, 54 and 42 Ma. Emplacement of volcanic rocks on the extra crust resulted from rapid northward motion (absolute) of the Indian plate. The Ninetyeast Ridge was originated when the spreading centers of the Wharton Ridge were absolutely moving northward with respect to a relatively stationary Kerguelen hotspot with multiple southward ridge jumps. In the process, the spreading center coincided with the Kerguelen hotspot and took place on-spreading-axis volcanism along the Ninetyeast Ridge.  相似文献   

Identification and characterization of marine geohazards in the deep water eastern offshore of India: constraints from multibeam bathymetry,side scan sonar and 3D high-resolution seismic data     

Rabi Bastia  M. Radhakrishna  Satyabrata Nayak 《Natural Hazards》2011,57(1):107-120

The eastern offshore of India covers a vast stretch of sedimentary tract fed by major rivers like Ganges, Brahmaputra and Mahanadi in the north, Krishna and Godavari in the center, and Cauvery and Palar in the south, which led to variations in shelf-slope characteristics, degree of slope and hence slope instability. The structure as well as seismic attribute maps prepared from multibeam bathymetry and high-resolution 3D seismic data set has been analyzed to identify various geohazards in the deep water offshore regions of the east coast of India. These can be categorized as slope instability, slope canyons, shallow gas, mass transport complexes, sediment waves, gas hydrates, gas chimney, mud volcanoes and shallow faults. The slope instability is primarily related to rapid sedimentation by the active river systems while the other geohazards are often developed in association with shallow gas flows and leakages. The bottom simulating reflectors (BSRs) identified in the seismic sections indicate the presence of gas hydrates. Rapid sedimentation, BSR formation, dissolution and expulsion of water as well as gas and their subsequent vertical migration are responsible for the formation of shallow gas-related hazards. The results from the above analysis are of immense help in minimizing the risk of shallow hazards during exploration, drilling and subsurface installation activities along the eastern Indian offshore.  相似文献   

Guest editorial for the special issue “Tectonics of Bay of Bengal and Arabian Sea with special emphasis on coastal and marine geohazards”     

K. S. R. Murthy  A. K. Chaubey  M. Radhakrishna 《Natural Hazards》2011,57(1):1-5

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Seismicity, gravity anomalies and lithospheric structure of the Andaman arc, NE Indian Ocean     

M. Radhakrishna  S. Lasitha  Manoj Mukhopadhyay 《Tectonophysics》2008,460(1-4):248-262

The Andaman arc in the northeastern Indian Ocean defines nearly 1100 km long active plate margin between the India and Burma plates where an oblique Benioff zone develops down to 200 km depth. Several east-trending seismologic sections taken across the Andaman Benioff Zone (ABZ) are presented here to detail the subduction zone geometry in a 3-D perspective. The slab gravity anomaly, computed from the 3-D ABZ configuration, is a smooth, long-wavelength and symmetric gravity high of 85 mGal amplitude centering to the immediate east of the Nicobar Island, where, a prominent gravity “high” follows the Nicobar Deep. The Slab-Residual Gravity Anomaly (SRGA) and Mantle Bouguer Anomaly (MBA) maps prepared for the Andaman plate margin bring out a double-peaked SRGA “low” in the range of − 150 to − 240 mGal and a wider-cum-larger MBA “low” having the amplitude of − 280 to − 315 mGal demarcating the Andaman arc–trench system. The gravity models provide evidences for structural control in propagating the rupture within the lithosphere. The plate margin configuration below the Andaman arc is sliced by the West Andaman Fault (WAF) as well as by a set of sympathetic faults of various proportions, often cutting across the fore-arc sediment package. Some of these fore-arc thrust faults clearly give rise to considerably high post-seismic activity, but the seismic incidence along the WAF further east is comparatively much less particularly in the north, although, the lack of depth resolution for many of the events prohibits tracing the downward continuity of these faults. Tectonic correlation of the gravity-derived models presented here tends to favour the presence of oceanic crust below the Andaman–Nicobar Outer Arc Ridge.  相似文献   

The problem of human waste disposal and preserving a clean environment     

B. P. Radhakrishna 《Journal of the Geological Society of India》2009,74(5):543

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Nehru’s ‘Discovery of India’ the role of science in India’s development     

B. P. Radhakrishna 《Journal of the Geological Society of India》2009,73(2):157-164

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Chemical evolution coefficients for the study of galactic evolution     

D. C. V. Mallik 《Astrophysics and Space Science》1980,69(1):133-145

A new evaluation of chemical evolution coefficients has been made using recent stellar evolution and nucleosynthesis data. The role of the low and intermediate mass stars in galactic nucleosynthesis has been emphasized. A significant amount of⁴He,¹²C and neutron-rich species is found to be contributed by these stars. Comparison with observed abundances suggests a primary origin of¹⁴N. The simple model of galactic evolution with the new coefficients has been used to derive the ratio of helium to heavy element enrichment in the Galaxy. The new stellar evolution data do not explain the large value of this ratio that has been determined observationally.  相似文献