Analysis of attenuation and dispersion of propagating wave due to the coexistence of three fluid phases in the pore volume     

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   

Water resource accounting for an iron-ore mining area in India     

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   

PALEOMAGNETIC STUDY OF IGNEOUS ROCKS OF GUPIS—SHAMRAN AREA,KOHISTAN ARC, PAKISTAN,NW HIMALAYA     

Mirza Naseer Ahmad  et al 《地学前缘》2000,(Z1)

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   

Glacial-interglacial changes in the surface water characteristics of the Andaman Sea: Evidence from stable isotopic ratios of planktonic foraminifera     

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   

Damage detection of 3D structures using nearest neighbor search method     

Ali Abasi  Vahid Harsij  Ahmad Soraghi 《地震工程与工程振动(英文版)》2021,20(3):702-722

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   

Comparison of dynamic stiffnesses of rigid square and rectangular foundations by DBEM and IBEM     

S. Ahmad  A. S. M. Israil  K. Chen 《国际地质力学数值与分析法杂志》1988,12(6):657-678

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   

High-frequency observations of southern pulsars     

Simon Johnston  Aris Karastergiou  Kyle Willett 《Monthly notices of the Royal Astronomical Society》2006,369(4):1916-1928

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Polar wandering path for India during the Precambrian     

Iqbal Hasnain  N. Ahmad  Rafi Ahmad 《Pure and Applied Geophysics》1973,104(1):539-543

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   

Propagation transhorizon au-dessus de la Méditerrannee Sud-Orientale (Mer de Libye)     

Michel Anastassiades  Leonide Carapiperis  Aris Nassopoulos 《Pure and Applied Geophysics》1969,75(1):175-184

Sommaire Une étude radiométéorologique en mer close, a été initiée par le Groupe Radiométéorologique de l'OTAN. Pour completer les resultats des mesures au dessus du Canal d'Otranto (Martina Franca-Corfou) publiées en collaboration avec le Groupe Italien du Service de l'Aeronautique Militaire, des mesures au dessus de la mer de Libye sur la partie SE de la Mediterranée, d'une liaison transhorizon de 725 km entre le Caire et la ville d'Ierapetra, ont été enterprises.Pour expliquer le mecanisme de cette propagation transhorizon, on a appliqué une méthode d'analyse, basée sur les courbes de distribution du champs reçue en fonction du pourcentage du temps, indiquée par l'un des auteurs (Anastassiadis). Les courbes de distribution Rayleigh ou SuperRayleigh, obtenues pendant la période chaude, indiquent un mécanisme de reflection diffusée, tandis que les courbes avec des pentes superieures d'une Rayleigh pure, pendant la periode froide indiquent un mécanisme de guidage. L'hypothèse ci-dessus est supportée par le fait que les variations en altitudes des surfaces isobares suivant les periodes chaudes ou froides, presentent un fort coefficient de correlation avec les intensités du champ reçu.

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Summary A radiometeorological study of VHF propagation along transhorizon paths over several parts of the Mediterranean sea, was initiated by the Radiometeorological Panel of NATO's Science Committee. After a study over the Otranto channel (Martina Franca-Corfu) performed in collaboration with the Italian group, in the present paper is investigated the 725 km, mainly over the Lybean sea transhorizon path Cairo City to lerapetra, located in the South cost of Creta island. Three years fieldstrengths measurements were analysed in Ierapetra center. Following the observed results, during the warm period of the year it is a good reception, while during the cold period the reception was very poor or inexistant.In order to explain the mechanism of this transhorizon propagation, a method of analysis based on the distribution curves, as indicated by one of the authors (Anastassiadis) was used. Rayleigh or super-Rayleigh distribution curves of the received signalstrength versus time percentage observed during the warm period indicate a diffused reflection mechanism while Sub-Rayleigh distribution observed during the cold period indicate a ducting mechanism. These results are supported by the close correlation observed between the variation in altitudes of isobaric surfaces and the location of volume following the warm or cold period of the year in which the diffused reflection mechanism is produced.

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Uranium and boron distributions related to metamorphic microstructure-evidence for metamorphic fluid activity     

R. Ahmad  C. J. L. Wilson 《Contributions to Mineralogy and Petrology》1981,76(1):24-32

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