• Volume 117, Issue 3

      June 2008,   pages  179-240

    • Editorial

      N Mukunda Satish R Shetye

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    • Active fault traces along Bhuj Fault and Katrol Hill Fault, and trenching survey at Wandhay, Kachchh, Gujarat, India

      Michio Morino Javed N Malik Prashant Mishra Chandrashekhar Bhuiyan Fumio Kaneko

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      Several new active fault traces were identified along Katrol Hill Fault (KHF).A new fault (named as Bhuj Fault,BF)that extends into the Bhuj Plain was also identified.These fault traces were identified based on satellite photo interpretation and field survey.Trenches were excavated to identify the paleoseismic events,pattern of faulting and the nature of deformation.New active fault traces were recognized about 1 km north of the topographic boundary between the Katrol Hill and the plain area.The fault exposure along the left bank of Khari River with 10 m wide shear zone in the Mesozoic rocks and showing displacement of the overlying Quaternary deposits is indicative of continued tectonic activity along the ancient fault.The E-W trending active fault traces along the KHF in the western part changes to NE-SW or ENE-WSW near Wandhay village.

      Trenching survey across a low scarp near Wandhay village reveals three major fault strands F1, F2,and F3.These fault strands displaced the older terrace deposits comprising Sand,Silt and Gravel units along with overlying younger deposits from units 1 to 5 made of gravel,sand and silt. Stratigraphic relationship indicates at least three large magnitude earthquakes along KHF during Late Holocene or recent historic past.

    • Magnetotelluric investigations for imaging electrical structure of Garhwal Himalayan corridor, Uttarakhand, India

      M Israil D K Tyagi P K Gupta Sri Niwas

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      Magnetotelluric investigations have been carried out in the Garhwal Himalayan corridor to delineate the electrical structure of the crust along a profile extending from Indo-Gangetic Plain to Higher Himalayan region in Uttarakhand,India.The profile passing through major Himalayan thrusts:Himalayan Frontal Thrust (HFF),Main Boundary Thrust (MBT)and Main Central Thrust (MCT),is nearly perpendicular to the regional geological strike.Data processing and impedance analysis indicate that out of 44 stations MT data recorded,only 27 stations data show in general,the validity of 2D assumption.The average geoelectric strike, N70°W, was estimated for the profile using tensor decomposition.2D smooth geoelectrical model has been presented,which provides the electrical image of the shallow and deeper crustal structure.The major features of the model are (i)a low resistivity (> 50𝛺 m),shallow feature interpreted as sediments of Siwalik and Indo-Gangetic Plain,(ii)highly resistive (< 1000 𝛺m)zone below the sediments at a depth of 6 km,interpreted as the top surface of the Indian plate,(iii)a low resistivity (> 10𝛺 m) below the depth of 6 km near MCT zone coincides with the intense micro-seismic activity in the region. The zone is interpreted as the partial melting or fluid phase at mid crustal depth.Sensitivity test indicates that the major features of the geoelectrical model are relevant and desired by the MT data.

    • Paleosol at the Archean–Proterozoic contact in NW India revisited – Evidence for oxidizing conditions during paleo-weathering?

      Manoj K Pandit Helga de Wall Narendra K Chauhan

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      A number of fine-grained sericite bearing pelitic,schistose lithologies occur along the Archean (Banded Gneiss Complex)–Proterozoic (Aravalli Supergroup)contact (APC)in the Udaipur valley in NW Indian craton.These Al-rich lithologies (subsequently metamorphosed)have been described as ‘paleosols ’,developed over a 3.3 Ga old Archean gneissic basement and are overlain by Paleopro- terozoic Aravalli quartzite.The paleosol was developed between 2.5 and 2.1,coincident with the globally recognized Great Oxidation Event (GOE).In previous studies these paleosol sections were interpreted to have developed under reducing environment,however,the finding of a ‘ferricrete ’ zone in the upper part of Tulsi Namla section (east of Udaipur)during the present study (in addition to earlier reported lithologies) has led to an alternative suggestion of oxygen-rich conditions during paleosol development.The Tulsi Namla paleosol section shows all the features characteristic of a complete paleosol section described from other Archean cratons.The paleosol includes sericite schist with kyanite as the prevalent Al-silicate in the lower part of profile while chloritoid and Fe-oxides typify the Fe-rich upper part.Alumina has remained immobile during the weathering process while Fe and Mn show a decrease in the lower part of the section and an abrupt rise in the upper part,in the ferricrete zone.The field and geochemical data indicate that the Tulsi Namla section is an in situ weathering profile and at least the upper part shows evidence of oxidizing conditions.

    • Seasonal variation in biomass and species composition of seaweeds stranded along Port Okha, northwest coast of India

      Mukund C Thakur C R K Reddy Bhavanath Jha

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      Port Okha coast,which is known for its luxuriant growth of a diverse assemblage of seaweeds on Saurashtra coast,is found to have abundant quantities of seaweeds being drifted and washed ashore every year.Studies conducted for quantifying the stranded seaweeds from May 2004 to April 2005 showed an average biomass value of 3.10 kg fresh wt/m2/month with maximum being 6.60 kg fresh wt/m2 in April.The stranded weeds constituted a total of 62 species during the entire study period.Of this,Rhodophyta ranked high with 26 species followed by Chlorophyta with 22 species and Phaeophyta with 14 species.The stranded seaweeds that were washed ashore provide valuable floristic information about the intertidal and near shore sub-tidal algae of the respective regions.Although natural senescence of seaweeds is one of the major factors,strong currents primarily forced by tides,also contribute to the uprooting and subsequent drifting of seaweeds on to the beach.This ultimately causes changes in floristic features of the existing algal beds.

    • Observations of unusual whistlers during daytime at Jammu

      K K Singh R P Patel J Singh B Kumar A K Singh R P Singh B L Koul Lalmani

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      In this paper,we report observations of unusual whistlers recorded at Jammu (geomag.lat.= 22° 26′N; 𝐿 =1.17), India on March 8, 1999 during the daytime. They are interpreted as one-hop ducted whistlers having propagated along higher 𝐿 -values in closely spaced narrow ducts from the opposite hemispheres. After leakage from the duct, the waves might have propagated in the earthionosphere waveguide towards the equator in surface mode.Tentative explanation of the dynamic spectra of these events is briefly presented.

    • On the impact of temperature on tropospheric ozone concentration levels in urban environments

      E Stathopoulou G Mihalakakou M Santamouris H S Bagiorgas

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      The influence of temperature on tropospheric ozone (O3)concentrations in urban and photochemically polluted areas in the greater Athens region are investigated in the present study.Hourly values of the ambient air temperature used for studying the urban heat island effect in Athens were recorded at twenty-three experimental stations while ozone concentration values were measured at three of the above-mentioned stations and for a period of two years (1996 –1997).The linear correlation between ozone concentration and air temperature values as well as the temporal variation of temperature and ozone concentration,for the above-mentioned experimental stations, were calculated and analysed.Moreover,a neural network approach was used for investigating the impact of temperature on the ozone concentration values over the greater Athens area.The neural network model used ambient air temperature as one of its input parameters and it was found that temperature is a predominant parameter,affecting considerably the ozone concentration values.

    • A note on India’s water budget and evapotranspiration

      T N Narasimhan

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      Some recent analyses of India ’s water budget are based on information attributed to the Ministry of Water Resources.An examination of the budget components indicates that they imply an evapotranspiration estimate that is significantly lower than what one may expect based on information from other sources.If such is the case,India ’s water resources situation may be more dire than is otherwise perceived.For,higher evapotranspiration implies correspondingly reduced availability of water for human use.It should be worthwhile to investigate and reconcile the apparent discrepancy between water budget and evapotranspiration,considering the importance of water in the national context.

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