• D P Rao

      Articles written in Journal of Earth System Science

    • Variability of the oceanic boundary layer characteristics in the northern Bay of Bengal during MONTBLEX-90

      V S N Murty Y V B Sarma D P Rao

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      Variability of the ocean surface boundary layer characteristics on daily time-scale is studied utilizing the 3-hourly hydrographic data collected at a stationary location (20°N, 89°E) in the Bay of Bengal during August (18th–31st) and September (9th–19th), 1990 under MONTBLEX-90 field programme. The daily variations of temperature, salinity, σ0, mixed layer thickness, stability, heat content and rate of change of heat content in the upper 100 m are discussed in relation to prevailing weather (depressions) and hydrographic conditions (influx of fresh water, presence of eddies). The mixed layer thickness is examined through temperatureand σ0-based criteria considering also the surface salinity in the latter. TheT-based mixed layer thickness is always higher than that of σ0-based thickness. The rate of change of heat content is also computed up to the depth of 20°C and 14°C isotherms which takes into account the vertical motion and hence divergence. With the development of a low into a deep depression close to the study area, intense upwelling of subsurface cold waters is noticed from 100 m to the bottom of the surface mixed layer (20m) from 18th to 20th August. The upwelling is weakened by 21st August when the depression moved away from the study location. This variation of upwelling is supported by the variation of surface mixed layer thickness, static stability at 30 m depth, heat content in the upper 100 m and the heat content up to the depth of 20°C isotherm from 18th to 21st August. The rate of change of heat content in the upper 100 m and up to the depths of 20°C and 14°C isotherms leads to net heat storage during August and to net heat depletion during September. This together with the net surface heat gain lead to an import (197Wm−2) and export (233 Wm−2) of heat during August and September respectively through horizontal advective processes. These advective processes are attributed to the presence and movement of a warm core eddy through the study location.

    • Tectonic evolution of Kutch sedimentary basin, western India


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      Lithological variations, circular spectral anomalies, geological structures such as folds, faults, lineaments and shear zones of Kutch sedimentary basin were interpreted using IRS-LISS III satellite data. Aeromagnetic data was also interpreted qualitatively and quantitatively and a number of anomalous magnetic zones, faults, lineaments and domal structures were mapped. Magnetic basement depths and thickness of sediments were also computed. A number of alternate basement ridges/highs/uplifted blocks and depressions/lows/downthrown blocks were delineated. The information obtained from satellite remote sensing and aeromagnetic data were then integrated and the results were compared with published literature on gravity, magnetic (ground), magnetotelluric and seismic data, and also with field geology and well data. Structural controls in spatial domain (latitude, longitude and depth) were derived by establishing spatial relationship among different geological structures with reference to the geological time scale. Numerous horst and graben structures (ridges and sub-basins) as well as a number of master faults were delineated which serve as vital information with regard to hydrocarbon prospects and earthquake vulnerability, respectively. Based on the information obtained from this integrated study, a conceptual tectonometamorphic model along with sedimentation and igneous activity (ophiolitic and basaltic) has been constructed which has a significant bearing on the sequence of events that occurred during the deformational history of Kutch sedimentary basin resulting into the present day tectonic configuration.

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