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641.
642.
Qazi Adnan Ahmad Guochen Wu Zong Zhaoyun Wu Jianlu Li Kun Du Tianwei Nasir Khan 《Geophysical Prospecting》2020,68(2):657-677
In exploration geophysics, the efforts to extract subsurface information from wave characteristics exceedingly depend on the construction of suitable rock physics model. Analysis of different rock physics models reveals that the strength and magnitude of attenuation and dispersion of propagating wave exceedingly depend on wave-induced fluid flow at multiple scales. In current work, a comprehensive analysis of wave attenuation and velocity dispersion is carried out at broad frequency range. Our methodology is based on Biot's poroelastic relations, by which variations in wave characteristics associated with wave-induced fluid flow due to the coexistence of three fluid phases in the pore volume is estimated. In contrast to the results of previous research, our results indicate the occurrence of two-time pore pressure relaxation phenomenon at the interface between fluids of disparate nature, that is, different bulk modulus, viscosity and density. Also, the obtained results are compatible with numerical results for the same 1D model which are accounted using Biot's poroelastic and quasi-static equation in frequency domain. Moreover, the effects of change in saturation of three-phase fluids were also computed which is the key task for geophysicist. The outcomes of our research reveal that pore pressure relaxation phenomenon significantly depends on the saturation of distinct fluids and the order of saturating fluids. It is also concluded that the change in the saturation of three-phase fluid significantly influences the characteristics of the seismic wave. The analysis of obtained results indicates that our proposed approach is a useful tool for quantification, identification and discrimination of different fluid phases. Moreover, our proposed approach improves the accuracy to predict dispersive behaviour of propagating wave at sub-seismic and seismic frequencies. 相似文献
643.
S. K. Chaulya M. K. Chakraborty M. Ahmad K. K. K. Singh R. S. Singh B. K. Tewary P. K. Gupta 《Environmental Geology》2000,39(10):1155-1162
A study has been conducted at the Bicholim iron-ore mine, North Goa, India to investigate the hydrogeological continuity
between the mine's open pit and surrounding villages. Water resource accounting by demarcating different watersheds has also
been carried out to analyse the major causes of groundwater scarcity in the region during dry periods. A resistivity survey
and a ground penetrating radar survey were completed around the periphery of open pits, the surrounding village areas and
Mayem Lake. The results of the two independent surveys and other related data confirm that there is no observable hydrogeological
continuity between the pits, nearby villages and Mayem Lake. Hence, there may not be any significant effect on surrounding
water resources due to mining or mine dewatering. Water resource accounting has revealed that only 15–20% of 3500 mm precipitation
per annum becomes part of the groundwater resource. The remainder of the annual precipitation is lost as heavy runoff, evapotranspiration
and subsurface capillary moisture. Closely spaced wells in the region have also aggravated the groundwater scarcity problem
due to draw down effects. Therefore, an effective water resource conservation plan is required for the region to overcome
the problem.
Received: 18 January 1999 · Accepted: 17 May 1999 相似文献
644.
Kohistan Sequence has been considered as island arc formed during the subduction of oceanic lithosphere at the leading edge of northward moving Indian continent.. Sedimentary sequences indicate that formation of the intra\|oceanic Kohistan arc began in early Cretaceous time. The isotopic data demonstrate the involvement of enriched, DUPAL type mantle, suggesting that Kohistan arc was formed at or south of the present equator (Khan et al., 1997). The Intra oceanic phase of Kohistan lasted until sometime between 102 and 85 Ma, when Kohistan collided with Asia. From this time until collision with India about 50 Ma ago, Kohistan existed as Andean\|type margin. This paleomagnetic study is from the volcanic and plutonic rocks exposed in Gupis\|Shamran area (west of Gilgit) in northern part of the Kohistan arc. According to geochronological data these rocks were formed 61~55Ma ago (Treloar et al., 1989), when Kohistan was existing as Andean\|type margin. Seven to nine samples were collected from nine sites of Shamran volcanics (58±1)Ma and from five sites of Pingal, Gupis, and Yasin plutons (Ar\|Ar hornblende ages ranges from 61~52Ma). On the basis of one Rb\|Sr age of (59±2)Ma from these plutons, the above\|mentioned Ar/Ar ages may be regarded as reasonable intrusion ages of these plutons (Searle, 1991). 相似文献
645.
S. M. Ahmad D. J. Patil P. S. Rao B. N. Nath B. R. Rao G. Rajagopalan 《Journal of Earth System Science》2000,109(1):153-156
Stable carbon and oxygen isotopic analyses of the planktonic foraminifera (Globigerinoides ruber) from a deep sea sediment core (GC-1) in the Andaman Sea show high glacial-to-Holocene δ18O amplitude of 2.1%o which is consistent with previously published records from this marginal basin and suggest increased
salinity and/or decreased temperature in the glacial surface waters of this region. A pulse of18O enrichment during the last deglaciation can be attributed to a Younger Dryas cooling event and/or to a sudden decrease of
fresh water influx from the Irrawady and Salween rivers into the Andaman Sea. High δ13C values observed during the isotopic stages 2 and 4 are probably due to the enhanced productivity during glacial times in
the Andaman Sea. 相似文献
646.
An innovative damage identification method using the nearest neighbor search method to assess 3 D structures is presented. The frequency response function was employed as the input parameters to detect the severity and place of damage in 3 D spaces since it includes the most dynamic characteristics of the structures. Two-dimensional principal component analysis was utilized to reduce the size of the frequency response function data. The nearest neighbor search method was employed to detect the severity and location of damage in different damage scenarios. The accuracy of the approach was verified using measured data from an experimental test; moreover, two asymmetric 3 D numerical examples were considered as the numerical study. The superiority of the method was demonstrated through comparison with the results of damage identification by using artificial neural network. Different levels of white Gaussian noise were used for polluting the frequency response function data to investigate the robustness of the methods against noise-polluted data. The results indicate that both methods can efficiently detect the damage properties including its severity and location with high accuracy in the absence of noise, but the nearest neighbor search method is more robust against noisy data than the artificial neural network. 相似文献
647.
In this work, the Direct and Indirect Boundary Element Methods as applied to dynamic soil structure interaction problems, are compared. Both the methods are used to find the dynamic stiffnesses of rigid surface and embedded foundations. For surface foundations, the results obtained by the two methods were very close for the frequency range considered, but for embedded foundations at higher frequencies, the Indirect Boundary Element Method produced erroneous values for the real part of vertical compliance. The possible reasons for this discrepancy are also studied in this paper. 相似文献
648.
Summary The recent radiometric dating on some Precambrian formations of India and the available paleomagnetic data have enhanced the possibility of deducing the Polar wander path for India during the remote past. The data indicate that India was in the northern hemisphere during the Precambrian times. This inference has also been substantiated by the paleoclimatic evidences. 相似文献
649.
The distribution of uranium and boron in polymetamorphosed, granulite facies schists and gneisses has been studied using particle track methods. The concentration and distribution of these elements when examined in relation to mineralogy and microstructure provide an insight into: (1) the behaviour of U and B in metamorphism, (2) the activity of a fluid phase in the metamorphic processes and (3) the nature of chemical processes during schistosity development. A low concentration of primary U occurs in micro-inclusions of apatite and zircon (many are metamict) in the granulite facies M1 assemblage. This assemblage which lacks B, except for zoned sillimanite, has undergone a localized retrograde metamorphism RM1 characterised by hydrous alteration products containing abundant U and B. The RM1 metamorphism is attributed to fluids generated during granulite facies dehydration reactions. A schistosity S2 defined by M2 fibrolite aggregates overprints the M1 events. It is associated with (1) intragranular U concentrated in M2 apatite and titanium bearing minerals and (2) abundant intergranular U within the fibrolite aggregates. High B contents also occur with the fibrolite. The S2 schistosity appears to develop in a metamorphic environment containing a fluid enriched in U and B. 相似文献
650.
In the methods used for determination of the hydraulic behaviour at large scale of fractured rock masses, based on the simulation of flow in a fracture network, the mean flux and the mean pressure gradient in the network are not rigorously determined. A method is given for deriving these quantities, in a heterogeneous permeable block, from pressure and flux values on the boundary of the block. A block conductivity tensor is then defined, based on the condition of linear variation of the pressure on the boundary of the block. It is shown that this conductivity tensor is symmetric and positive-definite. An example of application to a model of fractured medium is given. To cite this article: A. Pouya, A. Courtois, C. R. Geoscience 334 (2002) 975–979. 相似文献