首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 863 毫秒
1.
A new approach is proposed in order to interpret field self-potential (SP) anomalies related to simple geometric-shaped models such as sphere, horizontal cylinder, and vertical cylinder. This approach is mainly based on solving a set of algebraic linear equations, and directed towards the best estimate of the three model parameters, e.g., electric dipole moment, depth, and polarization angle. Its utility and validity are demonstrated through studying and analyzing synthetic self-potential anomalies obtained by using simulated data generated from a known model and a statistical distribution with different random errors components. Being theoretically tested and proven, this approach has been consequently applied on two real field self-potential anomalies taken from Colorado and Turkey. A comparable and acceptable agreement is obtained between the results derived by the new proposed method and those deduced by other interpretation methods. Moreover, the depth obtained by such an approach is found to be very close to that obtained by drilling information.  相似文献   

2.
A high‐resolution method to image the horizontal boundaries of gravity and magnetic sources is presented (the enhanced horizontal derivative (EHD) method). The EHD is formed by taking the horizontal derivative of a sum of vertical derivatives of increasing order. The location of EHD maxima is used to outline the source boundaries. While for gravity anomalies the method can be applied immediately, magnetic anomalies should be previously reduced to the pole. We found that working on reduced‐to‐the‐pole magnetic anomalies leads to better results than those obtainable by working on magnetic anomalies in dipolar form, even when the magnetization direction parameters are not well estimated. This is confirmed also for other popular methods used to estimate the horizontal location of potential fields source boundaries. The EHD method is highly flexible, and different conditions of signal‐to‐noise ratios and depths‐to‐source can be treated by an appropriate selection of the terms of the summation. A strategy to perform high‐order vertical derivatives is also suggested. This involves both frequency‐ and space‐domain transformations and gives more stable results than the usual Fourier method. The high resolution of the EHD method is demonstrated on a number of synthetic gravity and magnetic fields due to isolated as well as to interfering deep‐seated prismatic sources. The resolving power of this method was tested also by comparing the results with those obtained by another high‐resolution method based on the analytic signal. The success of the EHD method in the definition of the source boundary is due to the fact that it conveys efficiently all the different boundary information contained in any single term of the sum. Application to a magnetic data set of a volcanic area in southern Italy helped to define the probable boundaries of a calderic collapse, marked by a number of magmatic intrusions. Previous interpretations of gravity and magnetic fields suggested a subcircular shape for this caldera, the boundaries of which are imaged with better detail using the EHD method.  相似文献   

3.
Summary A common computer program for the interpretation of vertical magnetic anomalies of spheres and horizontal cylinders has been developed. The input consists of the observed anomalies noted against their distances measured from an arbitrary point in the profile and a code number for each model. The program is written so that the positions and magnitudes of the maximum and minimum anomalies are located and their ratios and signs are used to define the initial parameters of the model under consideration. The errors resulting from these approximate values are derived and are solved for the increments to be given to the initial values. The process is repeated until the sum of the squares of the errors is less than 0.25% of the sum of the squares of the observed anomalies. The method has been tested on various theoretical examples and the results justify the validity of the programme.  相似文献   

4.
An interpretation technique using the Mellin transform is suggested for the analysis of magnetic anomalies due to some two-dimensional structures namely (i) a vertical sheet of both finite and infinite depth extent, (ii) a thick dyke and (iii) a horizontal circular cylinder. The Mellin transformed magnetic anomalies resemble gamma functions which are amenable to an easy interpretation. This procedure is illustrated with a small number of synthetic examples in each case. The practicality of the method is exemplified with the well-known vertical magnetic anomalies of Kursk (USSR) in the case of an infinite sheet model and Karimnagar magnetic anomaly (India) in the case of a horizontal circular cylinder. The results are compared with the techniques already available and found to be reliable.  相似文献   

5.
Summary A novel method of interpreting gravity and magnetic anomalies is presented here. Two diagrams of master curves, one for gravity and the other for vertical magnetic interpretation are presented. They are useful in calculating the depth of burial and the radius of infinite horizontal cylindrical bodies irrespective of density contrast or strength and direction of magnetisation. This method also enables us to infer the direction of magnetisation, resultant intensity of magnetisation and from them the susceptibility contrast; and density contrast. ThoughHenderson [8]2) reported the applicability of continuations and derivatives in the interpretation of magnetic anomalies for the first time, the authors have treated them in a more exhaustive manner in the present paper to obtain valuable relationships.  相似文献   

6.
Summary A new method of interpreting the gravity and magnetic anomalies is introduced with special reference to the magnetic anomalies of a horizontal cylinder. The method consists of calculating the functions of the anomaly and its distance from an arbitrary point. These form a simple linear equation with coefficients related to the parameters defining the body. Since each observation forms a separate linear equation, the required normal equations are formed by the method of least squares and solved for the coefficients and hence for the various parameters defining the target. The discussion here is confined to the vertical magnetic anomalies. The application of the method to horizontal and total field anomalies of two dimensional bodies is also outlined.  相似文献   

7.
Magnetic anomalies are often disturbed by the magnetization direction, so we can’t directly use the original magnetic anomaly to estimate the exact location and geometry of the source. The 2D analytic signal is insensitive to magnetization direction. In this paper, we present an automatic method based on the analytic signal horizontal and vertical derivatives to interpret the magnetic anomaly. We derive a linear equation using the analytic signal properties and we obtain the 2D magnetic body location parameters without giving a priori information. Then we compute the source structural index (expressing the geometry) by the estimated location parameters. The proposed method is demonstrated on synthetic magnetic anomalies with noise. For different models, the proposed technique can both successfully estimate the location parameters and the structural index of the sources and is insensitive to noise. Lastly, we apply it to real magnetic anomalies from China and obtain the distribution of unexploited iron ore. The inversion results are consistent with the parameters of known ore bodies.  相似文献   

8.
Magnetic anomalies of complicated 3D sources can be calculated by using a combination of analytical and numerical integration. Two surfaces and the magnetization parameters (the amplitudes of the induced and remanent components and the direction cosines) of the source can be defined by arbitrary functions or by discrete data points in a plane. When combined with a polynomial magnetization function in the direction of the third axis, 3D magnetization distribution can also be modelled. The method gives very general equations for anomaly calculation. It can be used for direct modelling of sources interpreted by seismic or other methods and also for interactive interpretation with fast computers. It is possible to calculate anomalies of, for example, intrusives or folded sedimentary beds whose surfaces are functions of horizontal coordinates and which have polynomial magnetization variations in the vertical direction due to gravitational differentiation and arbitrarily varying magnetization in the horizontal direction due to regional metamorphosis. If the distribution of magnetization parameters in the vertical direction cannot be described satisfactorily by polynomials, models can be used whose surfaces are functions of the vertical coordinate and which can then have any arbitrary magnetization distribution in the vertical direction.  相似文献   

9.
The transformation from the gravimetric to the GPS/levelling-derived geoid using additional gravity information for the covariance function of geoid height differences has been investigated in a test area in south-western Canada. A “corrector surface” model, which accounts for datum inconsistencies, long-wavelength geoid errors, vertical network distortions and GPS errors, has been constructed using least-squares collocation. The local covariance function of geoid height differences is usually obtained from residual values between the GPS/levelling and gravimetric geoid heights after the elimination of all known systematic distortions. If additional gravity data (in the form of gravity anomalies) are available, the covariance function of geoid height differences can be determined by the following steps: (1) transforming the GPS/levelling-derived geoid heights into gravity anomalies; (2) forming differences between the computed in step 1 and given gravity anomalies; (3) determining the parameters of the local covariance function of the gravity anomaly differences; (4) constructing an analytical covariance model for the geoid height differences from the covariance function of the gravity anomaly differences using the parameters derived in step 3. The advantage of the proposed method stems from the great number of gravity data used to derive the empirical covariance function. A comparison with the least-squares adjustment shows that the standard deviation of the residuals of the predicted geoid height differences with respect to the control point values decreases by 2.4 cm.  相似文献   

10.
The magnetic anomaly due to a long tabular body usually consists of a maximum and a minimum. The distances and the amplitudes of the maximum and the minimum, when defined in dimensionless quantities, may be used as characteristics of the source. In this paper, a method based on the positions of the maximum and the minimum on the magnetic anomaly due to a long tabular body has been presented. Characteristic ratios,D andA involving the distances and amplitudes of the maximum and the minimum points on the anomaly curve are defined. Nomograms showing the variations ofD andA with the parameters of (1) the dike and (2) the vertical fault models are presented. The parameters of the causative source are evaluated from the two ratiosD andA and the nomograms, using some simple analytical relations presented here. From the nomograms, it is observed that (a) for a thick dike,A is always greater thanD, (b)A=D for a thin sheet and (c) for a vertical fault,A is always less thanD. Thus from the characteristic ratiosD andA it is possible to evaluate the source parameters and also to distinguish whether the source is a dike, sheet or a vertical fault. The method is fast and is applicable for the magnetic anomalies either in total, vertical or horizontal component. The method has been applied on two field examples and the results are found to be in close agreement with those obtained by using other methods. A simple method of locating the origin on the anomaly curve is included. The limitations of the method are also discussed.  相似文献   

11.
Summary Standard charts from which a complete solution of the vertical magnetic anomalies of dipping doublets can be obtained very rapidly are derived and presented. The most important distances to be scaled from the field profile are the distances between the maximum and minimum anomalies, half maximum anomalies and one-third maximum anomalies only. The use of the charts for claculating the various parameters and locating the origin is also incorporated.  相似文献   

12.
利用基于消去-恢复原理的最小二乘配置方法,对2009-2013年相对重力/GPS联合观测数据与EGM2008模型数据进行融合,更新了巴颜喀拉块体东缘地区的自由空气与布格重力异常场.基于该布格重力异常数据,以CRUST1.0地壳密度模型为初始条件,使用二维多边形棱柱体正演与非线性最小二乘反演方法,获取了巴颜喀拉块体东缘地壳分层密度结构.基于地壳不可压缩和均衡调整原理提出了计算垂向构造应力新方法,并结合上述地壳分层密度结构和地形数据计算了巴颜喀拉块体东缘垂向构造应力分布.结果表明,龙门山断裂带中南段蓄积了较高的正向构造应力(约40 MPa),马尔康周边地区蓄积了较高的负向构造应力(约—30 MPa).对研究区域1970年以来5级(Ms)以上地震进行统计发现,地震多发生在垂向构造应力梯度带上,垂向构造应力为正的地区易触发浅源地震,为负的地区易触发深源地震.在地壳横向变形强烈的区域,垂向构造应力与地震深度的对应关系减弱.  相似文献   

13.
Summary A direct method of interpreting magnetic anomalies due to two-dimensional prisms is presented here. Measurement of the first vertical derivative supplies additional information concerning the parameters. The normal ground magnetic profile, as well as the gradient profile will have symmetrical points whose distances from the origin are related to the width, depth and height of a two dimensional prism shaped body.  相似文献   

14.
The present study investigates the reconstruction of the 3D dynamics of a turbulent mesoscale eddy field driven at a depth by a baroclinic instability of the Phillips type. It uses a high-resolution primitive equation simulation as a testbed. The method of reconstruction is based on potential vorticity principles and extends an earlier approach (Lapeyre and Klein, J Phys Oceanogr 36:165–176, 2006) to a regime where the signature of surface density anomalies on the dynamics is weak. The crux and the originality of the reconstruction lie in the estimation from sea surface height and surface density anomalies of the interior quasigeostrophic potential vorticity (PV) anomalies and its subsequent inversion. The estimation of PV anomalies relies on the vertical correlation between PV anomalies and on the knowledge on stratification and horizontal gradients of background PV. PV anomalies are accurately estimated over the first 500 m of the water column and over a wide range of wavenumbers. Density anomalies play a minor role in the PV estimation, though their omission leads to an overestimation of PV by a factor of less than 2 at scales of order 20 km and less. Inversion of the estimated PV leads to a geostrophic streamfunction which in turn provides reliable reconstructions of the relative vorticity and vertical velocity (via the omega equation).  相似文献   

15.
A genetic algorithm (GA) is an artificial intelligence method used for optimization. We applied a GA to the inversion of magnetic anomalies over a thick dike. Inversion of nonlinear geophysical problems using a GA has advantages because it does not require model gradients or well-defined initial model parameters. The evolution process consists of selection, crossover, and mutation genetic operators that look for the best fit to the observed data and a solution consisting of plausible compact sources. The efficiency of a GA on both synthetic and real magnetic anomalies of dikes by estimating model parameters, such as depth to the top of the dike (H), the half-width of the dike (B), the distance from the origin to the reference point (D), the dip of the thick dike (δ), and the susceptibility contrast (k), has been shown. For the synthetic anomaly case, it has been considered for both noise-free and noisy magnetic data. In the real case, the vertical magnetic anomaly from the Pima copper mine in Arizona, USA, and the vertical magnetic anomaly in the Bayburt–Sar?han skarn zone in northeastern Turkey have been inverted and interpreted. We compared the estimated parameters with the results of conventional inversion methods used in previous studies. We can conclude that the GA method used in this study is a useful tool for evaluating magnetic anomalies for dike models.  相似文献   

16.
2018年精河5.4级地震前地磁日变化畸变异常分析   总被引：3，自引：0，他引：3       下载免费PDF全文
2018年10月16日新疆精河5.4级地震发生时,震中附近的台站不同程度上记录了地磁日变化畸变异常,如地磁总强度F02时每日一值空间相关异常、地磁垂直分量加卸载响应比异常、地磁低点位移以及地磁日变化空间相关异常等。统计震前观测到的所有地磁异常,并分析研究了其震前异常变化特征。得到如下结论:(1)从全国每日一值相关分析结果看,震前114天出现每日一值空间相关异常,异常高值台为乌鲁木齐和克拉玛依;(2)震前59天沿北天山断裂带分布的地磁台站加卸载响应比均成组出现超限的高值,且异常高值的空间分布跟震中位置有一定关联;(3)中国大陆地磁台站震前37天出现低点位移突变分界线,且异常集中于震中附近;(4)震前出现地磁垂直分量日变化空间相关异常,异常台站空间上也主要集中于北天山地区。因此地磁垂直分量日变形态及有关的计算方法短期内具有一定的预报效能,可为今后利用地磁方法预测地震积累经验和震例。  相似文献   

17.
The behaviour under seismic loading of inclined piles embedded in two idealized soil profiles, a homogeneous and a non-homogenous “Gibson” soil, is analysed with 3D finite elements. Two structures, modeled as single-degree-of-freedom oscillators, are studied: (1) a tall slender superstructure (H st = 12 m) whose crucial loading is the overturning moment, and (2) a short structure (H st = 1 m) whose crucial loading is the shear force. Three simple two-pile group are studied: (a) one comprising a vertical pile and a pile inclined at 25°, (b) one consisting of two piles symmetrically inclined at 25°, and (c) a group of two vertical piles. The influence of key parameters is analysed and non-dimensional diagrams are presented to illustrate the role of raked piles on pile and structure response. It is shown that this role can be beneficial or detrimental depending on a number of factors, including the slenderness of the superstructure and the type of pile-to-cap connection.  相似文献   

18.
地壳磁化强度模型和居里等温面   总被引：1，自引：0，他引：1       下载免费PDF全文
利用卫星观测的长波磁异常，用等效偶极源方法推导了中国地区的视磁化强度分布．因卫星的高度远大于磁性地壳的厚度，将视磁化强度转换成磁化强度的垂直积分，它代表地壳内磁性物质的区域变化，利用视磁化强度与地表热流相应关系，计算了中国的新疆和东部一些地区居里等温面的深度．新疆地区的居里面深度为35-50km，其分布形态与塔里木盆地和准噶尔盆地的地貌比较相似；中国东部一些地区居里面深度在20-40km之间，与一些作者用航磁等数据得到的居里深度十分接近．  相似文献   

19.
地壳磁化强度模型和居里等温面   总被引：3，自引：0，他引：3       下载免费PDF全文
利用卫星观测的长波磁异常，用等效偶极源方法推导了中国地区的视磁化强度分布．因卫星的高度远大于磁性地壳的厚度，将视磁化强度转换成磁化强度的垂直积分，它代表地壳内磁性物质的区域变化，利用视磁化强度与地表热流相应关系，计算了中国的新疆和东部一些地区居里等温面的深度．新疆地区的居里面深度为35-50km，其分布形态与塔里木盆地和准噶尔盆地的地貌比较相似；中国东部一些地区居里面深度在20-40km之间，与一些作者用航磁等数据得到的居里深度十分接近．  相似文献   

20.
The results of the first stage of the pilot project on the complex monitoring of the atmospheric and ionospheric parameters, conducted on the instructions of the Russian Federation Government in order to decrease risk of destructive earthquakes in the Far East, are presented. The experiment was performed before and during a strong (M = 6.3) earthquake that occurred on August 2, 2007, on Sakhalin. The meteorological data (relative humidity and temperature), cloudiness anomalies according to the TERRA and AQUA satellite data, thermal anomalies of outgoing IR radiation according to the NOAA satellite data, variations in the total electron content according to the GPS data, and tomographic reconstructions of the ionosphere vertical structure according to the TRANSIT satellite data have been analyzed. The indications, typical of earthquake preparation and previously presented in the publications devoted to studying earthquake precursors, have been detected in all analyzed parameters. Synchronism and localization of the anomalies, registered using different methods in different geophysical fields, make it possible to assume that these anomalies have a common source, which could be the earthquake preparation process that is explained using the developed complex model of the lithosphere-atmosphere-ionosphere coupling (LAIC).  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号