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1.
Refraction surveys conducted by the Oil & Natural Gas Commission in the Cambay Basin, Gujarat, Rajahmundry area, Andhra Pradesh and near Rajamahal Traps, West Bengal, have indicated longitudinal velocities of the order of 4.2 to 5.8 km/sec for the Traps. Measurements of velocities by Sonic log in wells drilled for oil in the Cambay basin yielded values, ranging from 4.8 to 5.1 km/sec. While Sonic log velocities compare well with field refraction measurements, published values for trap basalt determined in the laboratories in India by various workers indicate a consistently high value of 6.6–7.2 km/sec. The distinctly lower value obtained by refraction methods can be attributed to weathering effects, thickness of trap flows, unsuspected inter-trappeans, dispersion in layered rocks etc. The mean values for the Traps of the Cambay, Rajamundry and Rajmahal areas come out to 4.78, 4.10 and 4.81 km/sec respectively. 相似文献
2.
D. E. White 《Bulletin of Volcanology》1966,29(1):481-483
The potential of a geothermal area is primarily dependent on volume and temperature of the reservoir and adequacy of fluid supply. Inadequate fluid supply may be a more common limiting factor than inadequate heat supply, for heat stored in the upper 10,000 ft of many hot spring systems is 1,000 to 10,000 times their annual natural heat flow. Except in very porous reservoirs, most of this heat is stored in rocks rather than in pore fluids. Geothermal fields can be classified as hot spring systems or as deep insulated reservoirs with little surface expression; gradations also exist. Hot spring systems have high near-surface permeability, at least locally on faults and fractures, permitting fluids to escape at high rates. Owing to vigorous circulation and escaping fluids and heat, near-surface temperatures are high, but temperatures deep in the system are lower than would prevail with inhibited escape. Deep reservoirs with little surface expression require permeable reservoir rocks capped by insulating rocks of low permeability. Larderello, Italy, and Salton Sea, California, have slight leakage, but others may have no leakage. Liquid water, which can be at temperatures far above 100° C because of existing pressures, is generally the dominant fluid. Steam can form by boiling as hot water rises to levels of lower pressure. However, in several explored systems the heat supply is so high and rate of discharge of water so low that steam exists even deep in the system. Dry steam areas are probably rare. About 30 areas in the United States have been explored for geothermal energy, but dry steam has been proved only at « The Geysers ». Extensive utilisation of geothermal energy must therefore depend largely upon steam « flashed » from hot water with decrease in pressure. Problems that confront broad utilisation of geothermal energy include: 1) discovery of reservoirs with adequate supply of energy and natural fluids; 2) deposition of CaCO; or SiO2; 3) chemical corrosion; 4) objectionable chemicals in some effluents; and 5) inapplicability of existing public laws. The optimum environment for a geothermal reservoir includes:
- 1.Potent source of heat, such as a magma chamber. A depth of at least two miles provides enough pressure to insure water of high temperature; 5 miles may be too deep for effective transfer of heat to circulating water. Such heat sources are most likely to occur in regions of late Cenozoic volcanism. 相似文献
3.
The hyperbolic Radon transform has a long history of applications in seismic data processing because of its ability to focus/sparsify the data in the transform domain. Recently, deconvolutive Radon transform has also been proposed with an improved time resolution which provides improved processing results. The basis functions of the (deconvolutive) Radon transform, however, are time-variant, making the classical Fourier based algorithms ineffective to carry out the required computations. A direct implementation of the associated summations in the time–space domain is also computationally expensive, thus limiting the application of the transform on large data sets. In this paper, we present a new method for fast computation of the hyperbolic (deconvolutive) Radon transform. The method is based on the recently proposed generalized Fourier slice theorem which establishes an analytic expression between the Fourier transforms associated with the data and Radon plane. This allows very fast computations of the forward and inverse transforms simply using fast Fourier transform and interpolation procedures. These canonical transforms are used within an efficient iterative method for sparse solution of (deconvolutive) Radon transform. Numerical examples from synthetic and field seismic data confirm high performance of the proposed fast algorithm for filling in the large gaps in seismic data, separating primaries from multiple reflections, and performing high-quality stretch-free stacking. 相似文献
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3D Radon变换及其反变换是X-CT三维图像重建理论的核心,它在其他许多学科领域也有广泛应用。3D Radon变换的表达式是一个三重积分,按照定义直接计算相当费时。为此,研究一种新的快速的方法实现3D Radon变换,对X-CT图像重建理论及相关领域的发展有重要意义。本文以算法仿真常用椭球模型为基础,通过求解椭球模型与空间任意平面的面积,实现了用解析的方法快速得到模型的Radon变换,进一步比较了它与传统方法的优缺点,最后根据Radon反变换重建出原物体模型;计算机仿真结果验证了这种方法的正确。 相似文献
6.
We apply a newly developed numerical method to improve the Moho geometry by the implementation of gravity data. This method utilizes expressions for the gravimetric forward and inverse modeling derived in a frequency domain. Methods for a spectral analysis and synthesis of the gravity field and crust density structures are applied in the gravimetric forward modeling of the consolidated crust-stripped gravity disturbances, which have a maximum correlation with the (a priori) Moho model. These gravity disturbances are obtained from the Earth’s gravity disturbances after applying the topographic and stripping gravity corrections of major known anomalous crust density structures; in the absence of a global mantle model, mantle density heterogeneities are disregarded. The isostatic scheme applied is based on a complete compensation of the crust relative to the upper mantle density. The functional relation is established between the (unknown) Moho depths and the complete crust-stripped isostatic gravity disturbances, which according to the adopted isostatic scheme have (theoretically) a minimum correlation with the Moho geometry. The system of observation equations, which describes the relation between spherical functions of the isostatic gravity field and the Moho geometry, is defined by means of a linearized Fredholm integral equation of the first kind. The Moho depths are determined based on solving the gravimetric inverse problem. The regularization is applied to stabilize the ill-posed solution. This numerical procedure is utilized to determine the Moho depths globally. The gravimetric result is presented and compared with the seismic Moho model. Our gravimetric result has a relatively good agreement with the CRUST2.0 Moho model by means of the RMS of differences (of 3.5 km). However, the gravimetric solution has a systematic bias. We explain this bias between the gravimetric and seismic Moho models by the unmodelled mantle heterogeneities and uncertainties in the CRUST2.0 global crustal model. 相似文献
7.
高分辨率Radon变换方法及其在地震信号处理中的应用 总被引：32，自引：19，他引：13
Radon变换方法在地震资料处理中广泛采用,在地震同相轴识别和估计方面具有良好效果．无论是倾斜叠加,还是广义Radon变换方法,一般采用最小二乘反演方法实现．目前,在提高反演算法的效率和分辨率方面仍值得研究．本文从倾斜叠加的定义出发,阐明Radon变换分辨率问题的来源和解决办法．采用最小二乘反演方法研究高分辨率抛物线Radon变换和双曲Radon变换时,给出稀疏约束预条件共轭梯度法求解的高分辨率Radon变换的实现方法,同阻尼最小二乘方法相比,分辨率和精度明显提高,文中给出了模型算例．根据有效波和多次波NMO后剩余时差不同,采用高分辨率抛物线和双曲Radon变换可以压制多次波,分别给出了方法原理,最后给出应用实例．研究表明,稀疏约束预条件共轭梯度法可以有效实现高分辨率Radon变换;数值算例表明,算法计算效率和精度较高,可以更好地实现多次波压制． 相似文献
8.
为解决3D AVO地震数据快速保幅重建问题,在传统3D抛物Radon变换的基础上提出一种3D快速高阶抛物Radon变换方法.该方法将传统抛物Radon变换与正交多项式相结合,通过正交多项式系数描述地震数据AVO信息,确保重建后的地震数据具有良好保幅效果.同时,该方法引入新变量λ_x=q_xf和λ_y=q_yf,通过对q_xf和q_yf的整体采样,消除了3D高阶抛物Radon变换算子对频率的依赖,使变换算子的求逆过程仅需计算一次,大大节省计算时间.理论模型和实际地震资料的处理结果表明,该方法重建效率高,保幅效果良好. 相似文献
9.
The parabolic Radon transform has been widely used in multiple attenuation. To further improve the accuracy and efficiency of the Radon transform, we developed the 2- fdomain high-resolution Radon transform based on the fast and modified parabolic Radon transform presented by Abbad. The introduction of a new variable 2 makes the transform operator frequency-independent. Thus, we need to calculate the transform operator and its inverse operator only once, which greatly improves the computational efficiency. Besides, because the primaries and multiples are distributed on straight lines with different slopes in the 2-fdomain, we can easily choose the filtering operator to suppress the multiples. At the same time, the proposed method offers the advantage of high-resolution Radon transform, which can greatly improve the precision of attenuating the multiples. Numerical experiments suggest that the multiples are well suppressed and the amplitude versus offset characteristics of the primaries are well maintained. Real data processing results further verify the effectiveness and feasibility of the method. 相似文献
10.
ShuaiJun Wang FuYun Wang JianShi Zhang ShiXu Jia ChengKe Zhang JinRen Zhao BaoFeng Liu 《中国科学:地球科学(英文版)》2014,57(9):2053-2063
For the first time on the Chinese mainland, long-range wide-angle seismic reflection/refraction profiling technology has been applied to seismic wave phases from different depths and with different attributes within the various blocks of the North China Craton to characterize the structure of the crust and upper mantle lithosphere. By comparative analysis of the seismic wave phase characteristics in each block across a 1500-km-long east-west profile, we have identified conventional Pg, Pci, PmP and Pn phases in the crust, made a clear contrast between PL1 and PL2 waves belonging to two groups of lithospheric-scale phases, and produced a model of crust-mantle velocity structures and tectonic characteristics after one- and two-dimensional calculations and processing. The results show that the thickness of the crust and lithosphere gradually deepens from east to west along the profile. However, at the reflection/refraction interface, seismic waves in each group show obvious localized changes in each block. Also, the depth to the crystalline basement changes greatly, from as much as 7.8 km in the North China fault basin to only about 2 km beneath the Jiaodong Peninsula and Taihang-Lüliang area. The Moho morphology as a whole ranges from shallow in the east to deep in the west, with the deepest point in the Ordos Block at 47 km; in contrast, the North China Plain Block is uplifting. The L1 interface of the lithosphere is observed only to the west of Taihang Mountains, at a relatively slowly changing depth of about 80 km. The L2 interface varies from 75 to 160 km and shows a sharp deepening to the west of Taihang Mountains, forming a mutation belt. 相似文献
11.
Balasubramanian Balamuralikrishnan Vellingiri Balachandar Mohana Devi Subramaniam Karthick Kumar Alagumuthu Shanmugam Sureshkumar Meyyazhagan Arun Sundaramoorthy Arun Krishnan Padmavathi Abdul Hakkim Razeena Mohan Gomathi Palanivel Velmurugan Shahnaz N. Dharwadkar Keshavarao Sasikala 《Stochastic Environmental Research and Risk Assessment (SERRA)》2014,28(7):1801-1814
Chemicals, especially silica, have been suspected to cause genetic alterations in pottery industry workers. The present study aims to analyze the frequency of chromosomal aberrations (CA), micronucleus (MN) and DNA damage (comet assay) in the peripheral blood lymphocytes and the immunological alterations workers chronically exposed to silica and in control subjects. In our study, 50 silica exposed workers and 35 control subjects were recruited and silica level was measured by respirable dust and respirable quartz concentrations of badge dosimeter. The serum immunoglobulins (IgM, IgG, and IgA) of all the subjects were measured by using ELISA method. The individuals exposed to silica have a significant increase in the frequency of CA, MN and the total DNA damage (p < 0.05). Immunoglobulin elevation on silica exposed workers was statistically significant (p < 0.05) on comparison with their respective controls. Investigation of the smoking and alcohol habitats coupled with silica exposure in exposed and control subjects represents alcohol consumption and smoking as additional risk factors and must be avoided. Multiple linear regression analysis obtained for CA, MN and comet assay confirm these tests as biomarkers for silica exposed pottery workers. Some confounding factors also showed significant influence on exposed subjects. These results indicate the mutagenic risk in the working environment has a high probability of association with the silica dust exposure in pottery industries. Nevertheless, the present study will create awareness and public concern not only among the silica exposed workers but also to the welfare of their progeny. 相似文献
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Roberto Sulpizio Giovanni Zanchetta Benoit Caron Pierfrancesco Dellino Daniela Mele Biagio Giaccio Donatella Insinga Martine Paterne Giuseppe Siani Antonio Costa Giovanni Macedonio Roberto Santacroce 《Bulletin of Volcanology》2014,76(10):1-8
Volcanic ash produced during explosive eruptions can have very severe impacts on modern technological societies. Here, we use reconstructed patterns of fine ash dispersal recorded in terrestrial and marine geological archives to assess volcanic ash hazards. The ash-dispersal maps from nine Holocene explosive eruptions of Italian volcanoes have been used to construct frequency maps of distal ash deposition over a wide area, which encompasses central and southern Italy, the Adriatic and Tyrrhenian seas and the Balkans. The maps are presented as two cumulative-thickness isopach maps, one for nine eruptions from different volcanoes and one for six eruptions from Somma-Vesuvius. These maps represent the first use of distal ash layers to construct volcanic hazard maps, and the proposed methodology is easily applicable to other volcanic areas worldwide. 相似文献
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K. Laing Bladh 《Bulletin of Volcanology》1980,43(1):155-171
The rhyodactic O’Leary Porphyry which forms the Pleistocene (0.233±0.37 m.y.) volcanic domes of O’Leary Peak and Darton Dome in the San Francisco Volcanic Field (northern Arizona, U.S.A.) contains sanidine phenocrysts with oligoclase mantles (rapakivi texture). Rapakivi texture occurs worldwide in silicic rocks of many ages and has been attributed to various igneous and metamorphic processes. The O’Leary Porphyry contains both mantled and unmantled sanidine (both are Or63–69 Ab30–36An1), oligoclase and quartz phenocrysts, labradorite (An53Ab45Or2) and kaersutite xenocrysts and andesite xenoliths. The compositional range of oligoclase is the same (An11–26Ab70–80Orr–10) for the rapakivi mantles, the oligoclase phenocrysts, and the oligoclase crystals poikilitic within sanidines. Most mantles are discontinuous. The sanidine appears to have been resorbed prior to mantling. Experimental melting studies on the O’Leary Prophyry show that, for a 15 wgt.% water system, plagioclase crystallized prior to sanidine and quartz crystallized last. The O’Leary Porphyry, although inhomogeneous, plots on a Q-Or-Ab-An diagram well within the plagioclase stability field. Poikilitic plagioclases within sanidines further support crystallization of plagioclase prior to sanidine in the O’Leary Porphyry. Exsolution of a ternary feldspar to form a plagioclase mantle is the most commonly accepted igneous theory of rapakivi texture formation but has been eliminated as the origin of the O’Leary Porphyry rapakivi. Petrologic models by Tuttle and Bowen and by Stewart are rejected for the O’Leary rapakivi because of inconsistencies with the O’Leary occurrences. Two theories are viable for the O’Leary rapakivi texture. First, is a decrease in water vapor pressure which would enlarge the plagioclase stability field possibility causing mantling of metastable sanidines. The second and preferred theory is that of an addition of sodium and calcium by basification (chemical assimilation without melting) of the xenoliths within the O’Leary Porphyry. This would move the bulk composition of the melt into the plagioclase field possibly resulting in crystallization of plagioclase on sanidine crystals. Diffusion of sodium and calcium from the xenoliths to sanidine would result in mantling only those crystals near to the xenoliths. Later, convection would result in distribution throughout the melt of rapakivi, unmantled sanidines, and xenolithic kaersutite as is seen in the porphyry. Basic xenoliths are extremely common in rapakivi-bearing rocks. Those within the O’Leary Porphyry are andesitic and show resorption, and in some areas of O’Leary Peak itself, have been drawn out into schlieren. 相似文献
16.
This paper deals with the mineralogical, textural and chemical features of the dunite, peridotite, pyroxenite and gabbroic inclusions present in the Quaternary basalts of the Canary Islands. The mineralogical composition, structure and texture of the inclusions show that most of them have been formed as crystal cumulates from a nonalkaline basaltic magma in the earlier stages of its fractional crystallization. There are no co-genetic relationships between the inclusions and the host basalts, since the latter have a very strong alkaline-olivine character, although there are also some types with tholciitic aflinities. The study of the data leads to the conclusion that these inclusions can be considered as xenoliths from the basic and ultrabasic complexes that form the substratum and which outcrop in some of the Canary Islands. Attention is called to the fact that in many other volcanic zones of the world there has been a previous emplacement of basic and ultramafic layered complexes and is the question opened whether the association between stratiform-complexes and active basaltic volcanism is more frequent than has been assumed up to now. 相似文献
17.
Dario Pedrazzi Laura Becerril Joan Martí Stavros Meletlidis Inés Galindo 《Bulletin of Volcanology》2014,76(10):1-19
The Canary Islands consist of seven basaltic shield volcanoes whose submerged portion is much more voluminous than the subaerial part of each island. Like so many other volcanic oceanic islands, the indicative deposits of explosive felsic volcanism are not a common feature on the Canary archipelago. Hitherto, they have only been documented from the central islands of Gran Canaria and Tenerife, which are the largest volcanic complexes of the islands. On the other Canary Islands, the presence of felsic rocks is mostly restricted to intrusions and a few lava flows, generally within the succession in the oldest parts of individual islands. In this paper, we present a detailed stratigraphic, lithological and sedimentological study of a significant felsic pumice deposit on the island of El Hierro, referred here as the Malpaso Member, which represents the only explosive episode of felsic volcanism found on the Canary Islands (outside of Gran Canaria and Tenerife). The products of the eruption indicate a single eruptive event and cover an area of about 15 km2. This work provides a detailed stratigraphic and chronological framework for El Hierro, and four subunits are identified within the member on the basis of lithological and granulometric characteristics. The results of this study demonstrate the importance of an explosive eruption in a setting where the activity is typified by effusive basaltic events. Given the style and the spatial distribution of the Malpaso eruption and its products, a future event with similar characteristics could have a serious impact on the population, infrastructure and economy of the island of El Hierro. 相似文献
18.
M. ALI AK 《Geophysical Prospecting》1990,38(8):971-982
Seismic refraction surveying is still an important tool for determining the geometries and elastic wave propagation velocities of near-surface layers. Many analytical and graphical methods have been developed over the years for refraction interpretation, and these can be classified into two basic groups. The first group visualizes critically refracted rays converging on a common surface position, while the second group, which includes the wavefront methods, makes use of the critical rays emerging from a common point on the refractor. The method described in this paper is an analytical approach to the wavefront methods. The reverse refracted ray received by a geophone is intersected by the forward refracted rays received by subsequent geophones and a common critical refraction point on the refractor is estimated after a series of comparisons. This process is repeated for each geophone to yield the geometry and the velocity of the refractor. Several interpolations are performed to achieve a better accuracy. Palmer's models are used to test the efficiency of the algorithm. The results are presented together with those of other methods applied to the same models. 相似文献
19.
To give an indication on the influence of the dynamics and behavior of lake plankton on the seston composition in the outlet, four 24-hour sampling sessions were made in the Greifensee (situated near Zürich, Switzerland) and its outlet (River Glatt). The most important crustacean species studied wereEudiaptomus gracilis, Cyclops abyssorum, Cyclops vicinus, Mesocyclops leuckarti andDaphnia spp.Leptodora kindtii was found during one sampling only. No evidence of shore avoidance was found. The vertical migration in the lake especially in the upper layer (0–6 m) is believed to have an influence on the amount of plankton which is flushed into the outlet. Although the composition and concentration of the plankton at the deepest point of the lake have been known, no accurate predictions on the quality of the plankton close to shore or in the outlet were possible. 相似文献
20.
E. Ibarrola 《Bulletin of Volcanology》1969,33(3):729-777
More than two hundred new analyses of basaltic rocks from the Canary Islands are presented. The available data show that the earlier successions have similar variation trends throughout the archipelago; these trends represent all the intermediate types between basic differentiates (oceanites, ankaramites) and more salic differentiates (trachy-basalts, hawaiites). In the more recent volcanic series, the study shows that there is a magmatic diversification with different variation trends in the Eastern than in the Central Canary Islands. In the latter the alkaline character becomes stronger in the successive periods of volcanic activity which have been established in each island. In the Eastern islands the basaltic evolution is, on the contrary, towards basaltic rocks with tholeiitic affinities. 相似文献