Velocity of ground water percolation at Indaram, Godavari sub-basin, India     

Mohan L. Gupta  S. R. Sharma 《Journal of the Geological Society of India》2013,81(4):543-548

We present values of velocity of ground water percolation (Vg) over large depth intervals, varying from shallow to deeper depths in Indaram area of Godavari sub-basin. The velocities have been estimated using available measured geothermal data. Sub-surface temperatures were measured in seven boreholes. Terrestrial heat flow values are calculated using temperature data and measured values of thermal conductivity of core samples. The results show that Vg is ～3.4 ×10^?7 cm /sec in the top layers (70–150 m) and decreases to ～0.04×10^?7 cm/sec in the deeper levels around 350 m depth and becomes negligibly small thereafter, thereby, indicating that the overall permeability of the sub-surface layers, due to the occurrence of successions of permeable, semi-permeable layers gets reduced to more or less zero at depths around 350 m. The value of Thermal Peclet Number, which is the ratio of the heat transfer through convection to that through conduction, naturally becomes negligible around this depth in the area. The observed consistency of the magnitude of heat flow through various deep sections is a clear indicator that water percolation is practically reduced to zero at depths around 320–400 m and that conduction is the dominant mechanism of heat transfer below the inferred depth section, while the upper layers are dominated by recharge at various depths by near surface water from streams at Indaram.  相似文献   

Katol meteorite shower, Maharashtra: A preliminary study     

G. Suresh  S. H. Wankhade  Mohamed Shareef  Vivek P. Malviya  Binod Kumar  M. Mohan 《Journal of the Geological Society of India》2013,81(2):151-157

A meteorite shower occurred in Katol (21° 15′ 30″ N; 78° 35′ 00″ E; at an elevation of 415 m above msl), Nagpur district of Maharashtra state, India on May 22, 2012 between 14:00 to 14:30 hrs (Indian Standard Time) with a presently observed strewn field of ～5.0 sq km area. The event was experienced by the hundreds of inhabitants with a loud noise and fire ball between Akola in the west to Nagpur in the east. The Geological Survey of India has so far collected 27 meteorite pieces with a total weight of 3500 gm. The locations, size, shape and surface features of the individual meteorite pieces have been recorded. Based on their physical properties, mineralogy, mineral chemical mapping and REE chemistry, the Katol meteorites have been classified as olivine-rich H5 type differentiated stony meteorite with reconstituted chondrules. The preliminary evidence suggests the presence of pre-solar grains in Katol meteorite.  相似文献   

Unusual circulation pattern during Indian summer monsoon failure in July 2002 and June 2009   总被引：1，自引：0，他引：1  

Dhrubajyoti Samanta  Mihir Kumar Dash  Prem Chand Pandey 《Natural Hazards》2013,65(1):295-302

The circulation patterns over the Indian Ocean and the surrounding continents have been studied during June 2009 and July 2002 to explain the failure of Indian summer monsoon (ISM) rainfall. This study presents evidences that the failure of the ISM during these 2?months was probably due to the development of cyclonic circulation anomaly over the Western Asia and anticyclonic circulation anomalies downstream of Eastern Asia. These circulation anomalies were associated with the equatorward advection of cold air up to 10°N. This may be due to the equatorward intrusion of midlatitude Rossby waves. We hypothesize that the intrusion of midlatitude Rossby wave is responsible for breaking the east?Cwest circulation cell over the Indian region into two cells and weakening it. The weak east?Cwest cell reduces the strength of the easterly wind field usually present over the monsoonal region, thus reducing the cross-equatorial moisture transport into the Indian subcontinent and decreasing monsoon rainfall.  相似文献   

Hybrid attenuation model for estimation of peak ground accelerations in the Kutch region, India     

A. Joshi  Ashvini Kumar  K. Mohan  B. K. Rastogi 《Natural Hazards》2013,68(2):249-269

The Kutch region of Gujarat in India is the locale of one of the most devastating earthquake of magnitude (M _w) 7.7, which occurred on January 26, 2001. Though, the region is considered as seismically active region, very few strong motion records are available in this region. First part of this paper uses available data of strong motion earthquakes recorded in this region between 2006 and 2008 years to prepare attenuation relation. The developed attenuation relation is further used to prepare synthetic strong motion records of large magnitude earthquakes using semiempirical simulation technique. Semiempirical simulation technique uses attenuation relation to simulate strong ground motion records of any target earthquake. The database of peak ground acceleration obtained from simulated records is used together with database of peak ground acceleration obtained from observed record to develop following hybrid attenuation model of wide applicability in the Kutch region: $$ \begin{aligned} \ln \left( {\text{PGA}} \right) & = - 2.56 + 1.17 \, M_{\text{w}} - \, 0.015R - 0.0001\ln \left( {E + 15} \right) \\ &\quad 3.0 \le M_{\text{w}} \le 8.2;\quad 12 \le R \le 120;\quad {\text{std}} . {\text{ dev}}.(\sigma ): \pm 0.5 \\ \end{aligned} $$ ln ( PGA ) = ? 2.56 + 1.17 M w ? 0.015 R ? 0.0001 ln ( E + 15 ) 3.0 ≤ M w ≤ 8.2 ; 12 ≤ R ≤ 120 ; std . dev . ( σ ) : ± 0.5 In the above equation, PGA is maximum horizontal ground acceleration in gal, M _w is moment magnitude of earthquake, R is hypocentral distance, and E is epicentral distance in km. The standard deviation of residual of error in this relation is 0.5. This relation is compared with other available relations in this region, and it is seen that developed relation gives minimum root mean square error in comparison with observed and calculated peak ground acceleration from same data set. The applicability of developed relation is further checked by testing it with the observed peak ground acceleration from earthquakes of magnitude (M _w), 3.6, 4.0, 4.4, and 7.7, respectively, which are not included in the database used for regression analysis. The comparison demonstrates the efficacy of developed hybrid attenuation model for calculating peak ground acceleration values in the Kutch region.  相似文献   

Neoarchean suprasubduction zone arc magmatism in southern India: Geochemistry,zircon U-Pb geochronology and Hf isotopes of the Sittampundi Anorthosite Complex     

M. Ram Mohan  M. Satyanarayanan  M. Santosh  Paul J. Sylvester  Mike Tubrett  Rebecca Lam 《Gondwana Research》2013,23(2):539-557

The Sittampundi Anorthosite Complex (SAC) in southern India is one of the well exposed Archean layered anorthosite-gabbro-ultramafic rock associations. Here we present high precision geochemical data for the various units of SAC, coupled with zircon U-Pb geochronology and Hf isotopic data for the anorthosite. The zircon ages define two populations, the older yield a concordia age of 2541 ± 13 Ma, which is interpreted as the best estimate of the magmatic crystallization age for the Sittampundi anorthosite. A high-grade metamorphic event at 2461 ± 15 Ma is suggested by the upper intercept age of the younger zircon population. A Neoproterozoic event at 715 ± 180 Ma resulted in Pb loss from some of the metamorphic zircons. The magmatic age of the anorthosite correlates well with the timing of crystallization of the arc-related ~ 2530 Ma magmatic charnockites in the adjacent Salem Block, while the metamorphic age is synchronous with the regional metamorphic event. The geochemical data suggest that the rocks were derived from a depleted mantle source. Sub-arc mantle metasomatism of slab derived fluids and subsequent partial melting produced hydrous, aluminous basalt magma. The magma fractionated at depth to produce a variety of high-alumina basalt compositions, from which the anorthositic complex with its chromite-rich and amphibole-rich layers formed as cumulates within the magma chamber of a supra-subduction zone arc. The coherent initial¹⁷⁶Hf/¹⁷⁷Hf ratios and positive εHf values (1.7 – 4.5) of the magmatic zircons in the anorthosite are consistent with derivation of a rather homogeneous juvenile parent magma from a depleted mantle source. Our study further confirms that the southern part of the Dharwar Craton was an active convergent margin during the Neoarchean with the generation and emplacement of suprasubduction zone arc magmas which played a significant role in continental growth.  相似文献   

Depositional environment in and around Tamiraparani estuary,and off Tuticorin,Tamil Nadu,India: clues from grain size studies     

A.?Solai  M.?Suresh?GandhiEmail author  K.?Chandrasekaran  V.?Ram?Mohan 《Arabian Journal of Geosciences》2013,6(7):2419-2446

The sediments of the estuaries and offshore Tuticorin along the southern coast of Tamil Nadu were studied for their textural variation. Ninety sediment samples were collected from three sectors (river, estuary, offshore) on the basis of prevailing energy conditions and oceanographic parameters. Frequency curves show unimodal to bimodal in nature. Offshore samples also fall in bimodal with medium and fine sand where sediment is additionally deposited by the Tamiraparani River. The mean values ranging from 1.69 to 2.01 φ with medium to fine sand. The fine sand in the riverine region indicates the depositional nature of the sediments. In pre-monsoon, the standard deviation ranges from 0.29 to 0.81 φ, which falls in the very well sorted to moderately well sorted. Estuary ranges from 0.63 to 1.30 φ, with moderately sorted, whereas in the marine sediments ranges from 0.4 to 1.01 φ, with moderately to moderately well- sorted and some patches of poorly sorted is observed. In both monsoons, the grain size variations are mostly influenced in river and offshore samples compared to the estuaries. The CM pattern indicates the deposition of sediments in graded suspension. In estuary, the sediments are medium sand with moderately to poorly sorted, fine skewed which are indicative of denudation processes taking place there. In marine, the sediments are medium-to-fine, moderately-to-well sorted, and fine skewed to very fine skewed sediments, probably as a result of the influence of palaeo-sediments deposited by rivers from inland as well as by waves and currents from offshore. Further, the marine samples also highlight depositional processes.  相似文献   

On the Use of Roche Equipotentials in Analysing the Problems of Binary and Rotating Stars     

A. Pathania  A. K. Lal  C. Mohan 《Journal of Astrophysics and Astronomy》2013,34(1):69-73

Kopal (Adv. Astron. Astrophys., 9, 1, 1972) introduced the concept of Roche equipotentials to analyse the effects of rotational and tidal distortions in case of stars in binary systems. In this approach a mathematical expression for the potential of a star in a binary system is obtained by approximating its inner structure with Roche model. This expression for the potential has been used in subsequent analysis by various authors to analyse the problems of structures and oscillations of synchronous and nonsynchronus binary stars as well as single rotating stars. Occasionally, doubts have been expressed regarding the validity of the use of this approach for analysing nonsynchronous binaries and rotationally and tidally distorted single stars. In this paper we have tried to clarify these doubts.  相似文献   

Aeromagnetic anomalies uncover the Precambrian basement in the Chhattisgarh basin area,Central India     

Bahadur Ram  Nagendra Pratap Singh  A. S. Krishna Murthy 《Acta Geophysica》2008,56(4):982-993

This paper presents aeromagnetic images for the Chhattisgarh basin region, in Central India, to provide a new window on Precambrian basement geology and structure. On the basis of aeromagnetic patterns, the Chhattisgarh basin is sub-divided into a northern low (negative) anomaly zone and a southern high (positive) anomaly zone. The northern portion of the main Chhattisgarh basin has been further divided into two subbasins, the Hirri sub-basin in the west, and Baradwar sub-basin in the east. A prominent negative anomaly delineates a NW-SE trending greenstone belt separating these sub-basins. Positive magnetic anomalies delineate the extent of the Dongargarh granite and equivalents, while the weak magnetic anomaly in the southeast of the Dongargarh granite and equivalents reflect granulite gneisses of the Eastern Ghat Mobile Belt. By applying the reduced-to-the-equator filter we enhanced the possible magnetic sources and structural lineaments within the Chhattisgarh basin. A new sketch map of structural elements was then compiled from aeromagnetic interpretation over the Chhattisgarh basin area. It includes possible faults, folds and an inferred lithological boundary.  相似文献   

Urban mapping,accuracy, & image classification: A comparison of multiple approaches in Tsukuba City,Japan     

Rajesh Bahadur Thapa  Yuji Murayama 《Applied geography (Sevenoaks, England)》2009,29(1):135-144

The rapid growth of urban space and its environmental challenges require precise mapping techniques to represent complex earth surface features more accurately. In this study, we examined four mapping approaches (unsupervised, supervised, fuzzy supervised and GIS post-processing) using Advanced Land Observing Satellite images to predict urban land use and land cover of Tsukuba city in Japan. Intensive fieldwork was conducted to collect ground truth data. A random stratified sampling method was chosen to generate geographic reference data for each map to assess the accuracy. The accuracies of the maps were measured, producing error matrices and Kappa indices. The GIS post-processing approach proposed in this research improved the mapping results, showing the highest overall accuracy of 89.33% as compared to other approaches. The fuzzy supervised approach yielded a better accuracy (87.67%) than the supervised and unsupervised approaches. The fuzzy supervised approach effectively dealt with the heterogeneous surface features in residential areas. This paper presents the strengths of the mapping approaches and the potentials of the sensor for mapping urban areas, which may help urban planners monitor and interpret complex urban characteristics.  相似文献   

Parametric study of molecular line polarization in the solar atmosphere     

K. E. Rangarajan  D. Mohan Rao 《Journal of Astrophysics and Astronomy》2000,21(3-4):269-269

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