Efficient two-dimensional magnetotellurics modelling using implicitly restarted Lanczos method     

KRISHNA KUMAR  PRAVIN K GUPTA  SRI NIWAS 《Journal of Earth System Science》2011,120(4):595-604

This paper presents an efficient algorithm, FDA2DMT (Free Decay Analysis for 2D Magnetotellurics (MT)), based on eigenmode approach to solve the relevant partial differential equation, for forward computation of two-dimensional (2D) responses. The main advantage of this approach lies in the fact that only a small subset of eigenvalues and corresponding eigenvectors are required for satisfactory results. This small subset (pre-specified number) of eigenmodes are obtained using shift and invert implementation of Implicitly Restarted Lanczos Method (IRLM). It has been established by experimentation that only 15–20% smallest eigenvalue and corresponding eigenvectors are sufficient to secure the acceptable accuracy. Once the single frequency response is computed using eigenmode approach, the responses for subsequent frequencies can be obtained in negligible time. Experiment design results for validation of FDA2DMT are presented by considering two synthetic models from COMMEMI report, Brewitt-Taylor and Weaver (1976) model and a field data based model from Garhwal Himalaya.  相似文献   

Improvements in medium range weather forecasting system of India     

V S PRASAD  SAJI MOHANDAS  SURYA KANTI DUTTA  M DAS GUPTA  G R IYENGAR  E N RAJAGOPAL  SWATI BASU 《Journal of Earth System Science》2014,123(2):247-258

Medium range weather forecasts are being generated in real time using Global Data Assimilation Forecasting System (GDAFS) at NCMRWF since 1994. The system has been continuously upgraded in terms of data usage, assimilation and forecasting system. Recently this system was upgraded to a horizontal resolution of T574 (about 22 km) with 64 levels in vertical. The assimilation scheme of this upgraded system is based on the latest Grid Statistical Interpolation (GSI) scheme and it has the provision to use most of available meteorological and oceanographic satellite datasets besides conventional meteorological observations. The new system has an improved procedure for relocating tropical cyclone to its observed position with the correct intensity. All these modifications have resulted in improvement of skill of medium range forecasts by about 1 day.  相似文献   

Two layers of Australasian impact ejecta in the Indian Ocean?     

M. Shyam PRASAD  S. M. GUPTA  V. N. KODAGALI 《Meteoritics & planetary science》2003,38(9):1373-1381

Abstract— Only 2 Australasian tektites have been found in the Indian Ocean, and both are associated with surficial sediments. We collected cores from both locations where the tektites have been reported. The microtektites in these cores (and both the tektites, as reported earlier) have chemical compositions within the compositional range previously reported for Australasian tektites and microtektites. In both locations, while the tektites are occurring at the sediment/water interface, the microtektites are found buried in older horizons beneath the seafloor at stratigraphic levels, conforming to the radiometric age of the strewn field. Thus, at first glance, there appear to be 2 layers of Australasian impact ejecta in the Indian Ocean. However, the manganese nodules are associated with the tektites which, although millions of years old, are invariably resting on recent sediments. Therefore, the mechanism that retains nodules at the seafloor also seems to be operative on the tektites, thus leading to this apparent “age paradox” of tektite/microtektite distribution in the Indian Ocean, although they both belong to the same impact event.  相似文献   

Use of radon for evaluation of atmospheric transport models: sensitivity to emissions     

MOHAN L. GUPTA  ANNE R. DOUGLASS  S. RANDOLPH KAWA  STEVEN PAWSON 《Tellus. Series B, Chemical and physical meteorology》2004,56(5):404-412

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Holocene Floral and Faunal Remains Revealed Concealed Neotectonic Disturbance (Saria Tal, Kumaun Himalaya, India)   总被引：1，自引：1，他引：0  

Asha GUPTA 《《地质学报》英文版》2010,84(1):69-76

Palynological and paleontological investigations supported by the radiocarbon dates of the lacustrine sediments of two profiles from the temperate lake Saria Tal, in Naini Tal District, Kumaun Himalaya, have revealed the presence of a concealed fold at the region. The profile from bore cores represents the upper part of the Late Holocene and the profile from exposed sections from the Middle Holocene to the over middle part of the Late Holocene. The data generated from different investigations have uniformly indicated that the former profile represents normal superposition, while the latter represents the reverse order. The contemporary pollen as well as molluscan zones of both profiles are situated at different elevations but consist of similar bioremains – indicating continuation of the same strata in two profiles. The presence of reverse order of superposition, continuation of the same strata in two profiles at different elevations, and the orientation of biozones, have indicated that the revealed folding is of syncline type. The present study has also given an idea about the origin of this lake.  相似文献   

CHARACTERIZATION OF MAJOR,MINOR AND TRACE ELEMENTS IN SIX CCRMP (TDB-1, WGB-1, UMT-1, WPR-1, WMG-1 AND WMS-1) AND ONE IWG (ZW-C) GEOCHEMICAL CANDIDATE REFERENCE MATERIALS*     

Joy G. SEN GUPTA 《Geostandards and Geoanalytical Research》1994,18(1):111-122

Elemental compostions of six CCRMP (TDB-1, WGB-1, UMT-1, WPR-1, WMG-1 and WMS-1) and one IWG (ZW-C) geochemical candidate reference materials were determined by XRF, ICP-AES, ICP-MS, GFAAS and other modern instrumental techniques. Inter-method results compared favourably in the case of elements for which multiple data were available.  相似文献   

REPLY TO COMMENTS BY S. A. GREENHALGH*     

S. K. GUPTA 《Geophysical Prospecting》1977,25(2):385-387

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SCALE MODEL ELECTROMAGNETIC RESPONSE TO INLINE AND BROADSIDE SYSTEMS AT SKEW TRAVERSES OF A DIPPING HALF PLANE EMBEDDED IN A CONDUCTING HOST ROCK*     

O.P. GUPTA  M.S. JOSHI  J.G. NEGI 《Geophysical Prospecting》1980,28(1):119-134

Laboratory scale model experiments have been performed to obtain the electromagnetic response of a finitely conducting half plane embedded in resistive/conductive surrounding and excited by an oscillating magnetic dipole. Inphase and quadrature profiles are presented for two horizontal coplanar transmitter-receiver systems (inline and broadside) for normal and skew traverses and for different dips of the conductor. It is observed that the broadside system is more diagnostic in delineating the strike and dip of the conductor and is more sensitive to the conducting host rock. The broadside profile over a vertical or dipping half plane is characterized, when traversing perpendicular to strike, by two positive peaks flanking a zero response when the coils are over the top edge of the conductor. For skew traverses a negative peak replaces the zero response. An increasing asymmetry in the anomalies is caused by changing the dip of the conductor from the vertical in both the systems, but it is more pronounced for the broadside system. The quadrature response in the broadside system changes in a characteristic way when the target is surrounded by a conducting host rock. The comparative results of the two systems may, therefore, be useful in the induction prospecting for ore deposits approximated by a half plane, especially in delineating the strike, dip, and effect of conductive host rock.  相似文献   

SOME DETAILED INVESTIGATIONS ON INTERFACE WAVES*     

S. K. GUPTA 《Geophysical Prospecting》1975,23(2):275-291

In continuation of our earlier work on interface waves (Gupta and Martel 1971) we have extended our studies by using a plexiglas-steel combination in addition to plexiglas-brass. Two other emitter positions were also considered: emitter on plexiglas and emitter on the metal edge, a short distance away from the interface. In both cases the presence of an interface wave could be detected from the seismogram. A curved interface between plexiglas and brass was also studied and it was found that the curvature introduces a change in the phase velocity of the interface wave in the same way as a curved surface does for the Rayleigh wave.  相似文献   

CORRECTIONS FOR CONDUCTIVITY ESTIMATES IN INDUCTION PROSPECTING OF SULPHIDE DYKES IN A LAYERED ENVIRONMENT*     

J.G. NEGI  O.P. GUPTA  M.S. JOSHI 《Geophysical Prospecting》1987,35(6):718-734

In a weathered environment estimates of depth and conductance of metallic sulphide dykes from conventional anomaly index diagrams for a vertical half-plane in air have to be corrected, besides the usual corrections, for: 1. moderate conductivity of the host rocks, and 2. finiteness of strike length S and depth extent D. Model experiments have been carried out to evaluate the response variation of a vertical planar conductor with varying depth extent and strike length for both insulating and conductive surroundings. The results indicate: 1. A conductor with finite depth extent (D/L < 2.5) or strike length (S/L < 5.0) in an insulating medium yields a lower estimate of conductance (mineralization) and a greater depth. 2. A moderately-conductive host rock enhances the anomaly and rotates the phase so that the conductor appears to be more resistive (less mineralized) and shallower. The results have practical significance since in weathered surroundings a highly-mineralized body of finite size could be missed, or misjudged, because of low estimates of conductivity and depth.  相似文献