排序方式： 共有49条查询结果，搜索用时 15 毫秒
21.
Shib Sankar Ganguli Goutam Kumar Nayak Nimisha Vedanti V.P. Dimri 《Geophysical Prospecting》2016,64(2):456-468
For a magnetic target, the spatial magnetic signal can be expressed as a convolutional integral over Green's function of an assumed model with susceptibility as its parameter. A filter can be used to obtain the susceptibility by minimizing the mismatch between observed and the computed magnetic anomalies. In this perspective, we report the development of an advanced digital filter, which is efficient and can be used to map rock susceptibility from the acquired magnetic data. To design the new filter, we modified the space‐domain standard Wiener–Hopf filter by imposing two different constraints: (i) the filter energy constraint; and (ii) normalization of the filter coefficients. These constraints make it capable to characterize source bodies from their produced magnetic anomalies. We assume that the magnetic data are produced by induced magnetization only and interpretation can be as good as the subsurface model. Our technique is less sensitive to the data noise, which makes it efficient in enhancing the interpretation model. The modified filter demonstrates its applicability over the synthetic data with additive white Gaussian noise. In order to check the efficacy and adaptivity of this tool in a more realistic perspective, it is also tested on the real magnetic data acquired over a kimberlitic district adjoining to the western margin of the Cuddapah Basin in India to identify the source bodies from the anomalies. Our result shows that the modified Wiener–Hopf filter with the constraint for the magnetic data is more stable and efficient than the standard Wiener–Hopf filter. 相似文献
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23.
Maharana P. Kumar Dhirendra Kumar Rajesh Singh Rupendra Dimri A. P. 《Theoretical and Applied Climatology》2022,148(3-4):1459-1476
Theoretical and Applied Climatology - This study diagnoses the Satna flood event in the Tons River basin. The occurrence of this intense flood is attributed to the rainfall associated with the... 相似文献
24.
Study of seasonal climatology and interannual variability over India and its subregions using a regional climate model (RegCM3) 总被引：3，自引：0，他引：3
The temporal and spatial variability of the various meteorological parameters over India and its different subregions is high. The Indian subcontinent is surrounded by the complex Himalayan topography in north and the vast oceans in the east, west and south. Such distributions have dominant influence over its climate and thus make the study more complex and challenging. In the present study, the climatology and interannual variability of basic meteorological fields over India and its six homogeneous monsoon subregions (as defined by Indian Institute of Tropical Meteorology (IITM) for all the four meteorological seasons) are analysed using the Regional Climate Model Version 3 (RegCM3). A 22-year (1980–2001) simulation with RegCM3 is carried out to develop such understanding. The National Centre for Environmental Prediction/National Centre for Atmospheric Research, US (NCEP-NCAR) reanalysis 2 (NNRP2) is used as the initial and lateral boundary conditions. The main seasonal features and their variability are represented in model simulation. The temporal variation of precipitation, i.e., the mean annual cycle, is captured over complete India and its homogenous monsoon subregions. The model captured the contribution of seasonal precipitation to the total annual precipitation over India. The model showed variation in the precipitation contribution for some subregions to the total and seasonal precipitation over India. The correlation coefficient (CC) and difference between the coefficient of variation between model fields and the corresponding observations in percentage (COV) is calculated and compared. In most of the cases, the model could represent the magnitude but not the variability. The model processes are found to be more important than in the corresponding observations defining the variability. The model performs quite well over India in capturing the climatology and the meteorological process. The model shows good skills over the relevant subregions during a season. 相似文献
25.
Padhy Simanchal Mishra O. P. Subhadra N. Dimri V. P. Singh O. P. Chakrabortty G. K. 《Natural Hazards》2013,77(1):75-96
This study discusses the scaling properties of the spatial distribution of the December 26, 2004, Sumatra aftershocks. We estimate the spatial correlation dimension D 2 of the epicentral distribution of aftershocks recorded by a local network operated by Geological Survey of India. We estimate the value of D 2 for five blocks in the source area by using generalized correlation integral approach. We assess its bias due to finite data points, scaling range, effects of location errors, and boundary effects theoretically and apply it to real data sets. The correlation dimension was computed both for real as well as synthetic data sets that include randomly generated point sets obtained using uniform distributions and mimicking the number of events and outlines of the effective areas filled with epicenters. On comparing the results from the real data and random point sets from simulations, we found the lower limit of bias in D 2 estimates from limited data sets to be 0.26. Thus, the spatial variation in correlation dimensions among different blocks using local data sets cannot be directly compared unless the influence of bias in the real aftershock data set is taken into account. They cannot also be used to infer the geometry of the faults. We also discuss the results in order to add constraints on the use of synthetic data and of different approaches for uncertainty analysis on spatial variation of D 2. A difference in D 2 values, rather than their absolute values, among small blocks is of interest to local data sets, which are correlated with their seismic b values. Taking into account the possible errors and biases, the average D 2 values vary from 1.05 to 1.57 in the Andaman–Nicobar region. The relative change in D 2 values can be interpreted in terms of clustering and diffuse seismic activity associated with the low and high D 2 values, respectively. Overall, a relatively high D 2 and low b value is consistent with high-magnitude, diffuse activity in space in the source region of the 2004 Sumatra earthquake.
相似文献26.
Ravi P. Srivastava Nimisha Vedanti O. P. Pandey V. P. Dimri 《Journal of the Geological Society of India》2009,73(5):715-723
Vindhyan Basin of Central India situated just north of SONATA rift zone, forms one of the major geotectonic segment of the
Indian subcontinent which is associated with complex thermo-tectonic history. Southern part of this basin is known to contain
favorable conditions for hydrocarbon entrapment. Keeping this in view, a detailed gravity survey network comprising 40 gravity
bases and 1500 data points in an area of about 110 × 100 km2 was planned in and around Jabera-Damoh region. Analysis of Bouguer and free air gravity anomaly maps, prepared using fractal
based gridding method, indicates presence of two sedimentary basins (Jabera and Damoh) faulted on either sides beside ridge
like features. However, well-known Jabera domal structure appeared to be a shallow feature only. Inversion of gravity data
further reveals presence of 5 to 6 km thick Vindhyan sediments in the Jabera basin which are underlain by Mahakoshal/Bijawar
group of rocks, resting directly over the lower crust, thereby indicating almost total absence of granitic crust from this
region. It appears that due to an underlying thermal anomaly, the entire region may have been subjected to sustained uplift,
deformation, erosion and consequent crustal extension during early to mid Proterozoics which brought high velocity mafic crust
to such shallow levels. 相似文献
27.
Depth Estimation from the Scaling Power Spectral Density of Nonstationary Gravity Profile 总被引：1，自引：0，他引：1
-- A technique to estimate the depth to anomalous sources from the scaling power spectra of long nonstationary gravity profiles is presented. The nonstationary profile is divided into piecewise stationary segments based on the criterion of optimum gate length in which the time-varying and time-invariant autocorrelation functions are similar. The division of a nonstationary into piecewise stationary allows identification of the portion of the crust with different geological histories, and using the stationary portion of the gravity profiles, more consistent depths to the anomalous sources have been obtained. The technique is tested with the synthetic gravity profile and applied along the Jaipur-Raipur geotransect in western and central India. The geotransect has been divided into four stationary parts: Vindhyan low, Bundelkhand low, Narmada rift and Chhattisgarh basin; each section corresponding to a different geological formation. Forward modeling of gravity data using results of each stationary section is carried out to propose the subsurface structure along the Jaipur-Raipur transect. 相似文献
28.
Ravi Prakash Srivastava Nimisha Vedanti V. P. Dimri 《Pure and Applied Geophysics》2007,164(10):2009-2022
Fractal dimension analysis was carried out for optimal designing of 2-D gravity survey network and to determine an optimum
range of gridding interval to generate least aliased Bouguer anomaly maps. As a test case, this method has been successfully
applied to the Jabera-Damoh region of the Vindhyan Basin, which is considered as a potential hydrocarbon bearing area. In
particular, we aim to delineate accurately the lateral extent of a possible hydrocarbon bearing structure. To achieve this
aim, fractal dimension of survey network was computed using 2-D distributions of observation points in the planning phase
of the survey so that the optimum station spacing for gravity survey can be obtained. A range of optimum gridding interval
for the gravity data set was suggested using the box-counting method of fractal dimension determination. Bouguer anomaly maps
of the region are prepared utilizing the optimum gridding interval. For the first time, these anomaly maps clearly outline
the gravity evidence of an anomalous rifted structure, which is bounded by parallel faults on either side. This structure
is interpreted as a favorable basin for the occurrence of hydrocarbons. Another finding of this study has been the delineation
of an apparently small ridge-like structure running east-west, dividing this basin in two parts. A subsurface geological model
along a profile across the Jabera structure has also been presented. 相似文献
29.
A. P. Dimri 《Theoretical and Applied Climatology》2007,90(1-2):49-63
Summary The western Himalayas receive higher precipitation than the eastern Himalayas during the winter season (December–March). This
differential pattern of winter precipitation over the Himalayas can be attributed to topography and to a higher frequency
of disturbances over the western Himalayas, which result in variations in the circulation features. These circulation features,
in turn, result in variations in the meridional transport of heat, momentum, potential energy, and moisture across the Himalayas
due to mean and eddy motion.
Significant meridional transport due to mean motion takes place in the upper troposphere at 300 hPa and 200 hPa. Transport
east of 100° E dominates the transport over the western Himalayas. The eddy transport of heat, momentum, and potential energy
is considerably smaller than that due to mean motion. Eddy transport magnitudes are smaller up to 500 hPa and increase rapidly
aloft to 300 hPa and 200 hPa. Eddy transport over the western Himalayas is greater than over the eastern Himalayas. 相似文献
30.
Ashutosh Chamoli Anand K. Pandey V. P. Dimri P. Banerjee 《Pure and Applied Geophysics》2011,168(5):827-844
The gravity response and crustal shortening in the Himalayan belt are modeled in detail for the first time in the NW Himalaya.
The Bouguer gravity anomaly along a ~450-km-long (projected) transect from the Sub-Himalaya in the south to the Karakoram
fault in the north across the Indus-Tsangpo Suture Zone is modeled using spectral analysis, wavelet transform and forward
modeling. The spectral analysis suggests three-layer interfaces in the lithosphere at 68-, 34- and 11-km depths corresponding
to the Moho, the Conrad discontinuity and the Himalayan decollement thrust, respectively. The coherence, admittance and cross
spectra suggest crustal shortening because of convergence compensated by lithospheric folding at 536- and 178-km wavelength
at the Moho and the upper-crustal level. An average effective elastic thickness of around 31 km is calculated using the coherence
method. The gravity data are modeled to demarcate intracrustal to subcrustal regional thrust/fault zones. The geometrical
constraints of these faults are obtained in the space scale domain using the wavelet transform, showing good correlation with
the major tectonic boundaries. The crustal configuration along the transect shows how the Moho depth increases from 45 to
80 km towards the north with the locus of flexure of the Indian crust beneath the Higher Himalayan zone. The combination of
forward modeling and wavelet analysis gives insight into the subsurface extent and geometry of regional structures across
the NW Himalaya. 相似文献