共查询到20条相似文献，搜索用时 78 毫秒
1.
I. R. Qureshi 《Pure and Applied Geophysics》1976,114(1):81-94
Summary A mass distribution which remains constant perpendicular to a diameter, within the walls of a vertical cylinder, is defined as a bounded two-dimensional mass distribution. Assumption of such a distribution may be more realistic than the assumption of an unbounded two-dimensional distribution in many situations. The gravity effect of such a distribution is comparable with the effect calculated by conventional three-dimensional methods of reduction. The effect of sphericity of the earth may be allowed as an additional correction. For the calculation of the gravitational effect of this distribution, a formula for the attraction of a cylindrical strip, at a point on the axis, is derived. The effect is compared with that of a two-dimensional distribution. To calculate the effect of sphericity, a formula for the attraction of a spherical cap is derived and this attraction is compared with that of a flat disc. The proposed distribution and the correction for sphericity are particularly applicable in marine gravity reductions. 相似文献
2.
A method is described to locate secondary faults, which can be difficult to identify on the Bouguer gravity map. The method is based on cross-correlation between the theoretical anomaly due to a vertical step and the second vertical derivative of the Bouguer anomaly. Faults are located from the closed maxima and minima on the cross-correlation contour map calculated for two perpendicular directions. One-dimensional model computations show that the magnitude of the extremum of the cross-correlation is related to the depth to the top of the hanging wall and the throw of the fault. Application of the method to the Bouguer gravity map of the former mouth of the Yellow River in the Shengli Oilfield area near the Bo Hai Sea shows the effectiveness of the method. 相似文献
3.
Dezső Nagy 《Pure and Applied Geophysics》1965,62(1):5-12
Summary A computational scheme has been derived to generateHeuman's Lambda function. This has been applied to compute the gravitational attraction of a right vertical circular cylinder. Test computations show that the error introduced by assuming a semifinite cylinder in place of a finite one of depth 30 times its radius is 1.77%. 相似文献
4.
华北地区重力场与沉积层构造 总被引：12，自引：2，他引：12
位于中朝准地台的华北地区是由几个不同的断块组成的,重力异常场的分布具有很强的浅部效应、块状分布和深浅叠加场的特点。重力的高程效应很复杂,不同波长的起伏变化有不同的影响系数。本文对布格改正的有关问题进行了讨论,指出华北如区表浅层的密度值偏低（2520kg/m3）,该区合理的布格改正公式为△g2=-0.0879H。将重力场的垂直导数和向上延拓结合起来,有利于揭示地壳上部构造特征。本文搜集整理了由第四系到寒武系的沉积层资料,给出了沉积层总厚度和视密度的分布。对深部重力异常的分析表明,华北沉积层的形成有深源性质,在均衡调节中起着一定的内载荷作用。 相似文献
5.
6.
D. J. WOODWARD 《Geophysical Prospecting》1975,23(3):526-532
Formulae for the gravitational attraction, at a point, of vertical triangular prisms with oblique ends are presented. They are suited to computation on an electronic computer and are useful for determining the thickness of sediments in a sedimentary basin by iterative means. 相似文献
7.
P. VALLABH SHARMA 《Geophysical Prospecting》1967,15(2):167-173
A nomogram is presented which enables evaluation of the components of magnetic attraction of a homogeneous finite rectangular prism, and of gravitational attraction due to a uniform rectangular lamina. In practice any three-dimensional body could be approximated by a number of right rectangular prisms of varying dimensions governed by the shape of the body. The magnetic attraction of the whole body is then obtained by numerical summation of the effects of the constituent prisms. For evaluating the gravitational effect, the cross-section of the body corresponding to each elevation contour is approximated by a number of rectangular laminae (or by a stepping polygon) the attraction of which can be determined with the aid of the same nomogram. The total gravitational attraction of the body is obtained by a process of graphical integration along the vertical axis. 相似文献
8.
The prism method for terrain corrections using digital computers 总被引：1，自引：0，他引：1
Dezső Nagy 《Pure and Applied Geophysics》1966,63(1):31-39
Summary In the prism method of making terrain corrections, the topography is approximated by a model consisting of right rectangular prisms. The vertical component of the gravitational attraction of each prism is calculated and the sum of these components gives the terrain correction.The prism method as programmed has no computational limitations. It can be used on all sizes of computers; it can be applied to a large area with any fine grid interval; it can be processed in a single run and yet provides complete flexibility for both research and routine computations. This has been achieved by breaking up larger areas into regions which fit into the computer memory. The contributions of these regions are automatically summed up for each station. While processing each region, various controls may be used at each station to exclude the contribution of a distant part of the area, to use approximate expressions farther from the station, to print out details around the station. There is also provision to refine the model by using smaller prisms around each computation point. Thus full use of elevation control can be made to calculate the terrain correction, the accuracy of which depends only on the quality of the input data.The prism method has been used to calculate terrain corrections for 130 stations in the New Quebec crater area. For five of these stations terrain corrections were also calculated by usingHammer's template. The two independent sets of values differ by less than four per cent. 相似文献
9.
Jos Fernndez Kristy F. Tiampo John B. Rundle Gerhard Jentzsch 《Journal of Geodynamics》2005,39(5):475-492
A method for the computation and interpretation of gravity and height changes and vertical gravity gradients produced by magmatic intrusions in a layered elastic–gravitational medium is presented. The methodology assumes a planar medium geometry, which consists of welded layers overlying a half-space. The medium is elastic and gravitating. The intrusion is treated as a point source and can be located at any depth inside the medium. The theoretical elastic–gravitational model allows the computation of the so-called geometric and orthometric vertical displacements as well as gravity changes of different types. The corresponding vertical gravity gradients can also be computed. We present several examples of theoretical computations and study different types of these geometric and orthometric gravity gradients and the information we can get from the application of the methodology described. The results presented show that the use of these gradients is a useful tool to obtain information on the dynamics of the injection processes, including the detection of new magma recharge. We show that using the elastic–gravitational deformation model we can explain non-linear gravity–height relationships that appear in volcanic areas. We also present the application of the methodology to Mayon volcano, Philippines, delineating the intrusion of new magma, consistent with the produced eruptions after the observation period. 相似文献
10.
P. Vallabh Sharma 《Pure and Applied Geophysics》1966,64(1):14-18
Summary A simple method is presented for computing the gravity and magnetic profiles across two-dimensional bodies of arbitrary shape. The computer programme makes use of expressions for the attraction caused by an infinitely long sheet and it takes only a few seconds to compute a profile both for gravity and magnetic anomalies and their vertical and horizontal derivatives. Accuracy of the method is shown to be as good as that of graticules and owing to the use of simpler formulae, the method appears to be faster than the method of polygons. 相似文献
11.
本文提出一种基于重力/GPS联合观测数据计算垂向构造应力的新方法.计算步骤如下:(1)通过重力/GPS联合观测数据计算布格重力异常;(2)依据布格重力异常数据推算莫霍面深度;(3)依据GPS观测数据,通过均衡理论计算均衡面深度;(4)依据莫霍面与均衡面之间剩余物质(壳幔物质密度差)所承受的附加浮力,计算地壳承载的垂向构造应力.本文利用上述构造应力新算法,计算了巴颜喀拉块体东边界及周边地区垂向构造应力分布,发现龙泉山断裂带以东地区垂向构造应力基本为零,龙泉山断裂带与龙门山断裂带之间地区垂向构造应力为正值,巴颜喀拉地块东部垂向构造应力为负值.鲜水河断裂带东南段周边蓄积了-40~-50 MPa的垂向构造应力,且梯度变化剧烈;松潘高原蓄积的垂向构造应力大约为-10~-20 MPa,相对较小. 相似文献
12.
A. K. GOODACRE 《Geophysical Prospecting》1973,21(1):66-69
The use of arctangents rather than arcsines in the expression for the gravitational attraction of a homogeneous rectangular prism reduces computational difficulties. Once a subroutine is available to compute one component of attraction in a Cartesian coordinate system, the other components may be obtained by cyclic permutation of the field point and body coordinate parameters. This technique also readily provides derivatives of the gravitational attraction and hence forms a compact method for the calculation of a magnetic anomaly due to a homogeneous rectangular magnetic prism. 相似文献
13.
The EGM08 geopotential model complete to degree and order 2159 was used in a remove-compute-restore (RCR) method for the geoid
computation in the State of Rio de Janeiro, Brazil. Terrain and indirect effect corrections were computed using a 6-arcsec
resolution DTE, derived from the TOPODATA Project (Shuttle Radar Topography Mission data) raised by the National Institute
for Space Research. INPE, Brazil. We applied Voronoi/Delaunay discretisations for discrete Stokes integration. In these schemes,
target area is partitioned into polygons/triangles, respectively, and the computation is carried out by point-wise numerical
integration and no gridding is mandatory. For both procedures, the cells were produced using either observed gravity data
combined with gridded Bouguer derived information. Particularly in Delaunay scheme, as the gravity anomalies are interpolated
into the triangular cells, and geoid undulations are computed for their vertices, Stokes function singularity was gone. Externally
estimated errors resulting from a comparison with GPS/leveling data were presented for both the schemes and classical ones,
as well as for the EGM08 undulations. They yielded RMS differences equal to 0.105 m, 0.110 m, 0.110 m, 0.115 m and 0.228 m,
respectively, for Voronoi, Delaunay, Voronoi/Delaunay with gridded-data alone and EGM08, computed between 32 GPS/leveling
points. 相似文献
14.
15.
D. LYNESS 《Geophysical Prospecting》1985,33(4):567-576
A series of gravity measurements were taken over a period of time (c. 150 days each) above two adjacent working coal faces. Precise levelling and gravity measurements were taken along the same profile before, during, and after seam extraction. The observed change in gravity agrees well with the levelling data. The combined data sets illustrate the validity of a simple Bouguer relationship for the gravity gradient. The results of two-dimensional modelling are used to estimate the gravitational effect of the extracted material. A local feature detected only on the gravity signal may be due to an outcropping limestone layer. This controlled experiment demonstrates the possibility of using high-precision gravity measurements as a substitute for levelling, particularly in surveys of large areal extent where the cost of obtaining comprehensive coverage by levelling may be prohibitive. 相似文献
16.
N.P.J. O&#x;Hora 《Physics of the Earth and Planetary Interiors》1973,7(1):92-96
Deflexions of the vertical due to changes in luni-solar gravitational attraction can be determined by astronomical observations and the measures are of great importance in the derivation of values for parameters defining elastic properties of the earth. The primary purpose of the observations is the determination of time or latitude, or both, and the systematic deflexions of the vertical are small in comparison with the scatter of the observations so that regular observations made over a number of years are required for the detection of these effects. Eleven years of time and latitude observations made with the Herstmonceux Photographic Zenith Tube have been separately analysed and the two solutions reveal with great clarity the magnitudes and phases of the variations associated with tidal activity. The results are complicated because at Herstmonceux the deflexions arising directly from changes in the gravitational attraction of the moon have associated with them deflexions caused by changes in the attraction of the proximate waters of the English Channel which is itself affected by complex tidal activity. 相似文献
17.
A statistical technique, based on the concept of a 1D energy density spectrum of the observed gravity field, has been used to compute ensemble average depths to various horizons containing causative sources of random geometric shape, size, density, etc. The plot of the logarithm of the energy of the observed Bouguer anomaly versus the angular frequency can be approximated, over a certain frequency band, by a linear segment whose slope is related to an average ensemble depth around which a random distribution of numerous anomalous sources exists. Suitable matched filters, based on the computed values of intercepts and slopes of several linear segments approximating the spectrum, have been used to deconvolve the gravity effects associated with the causative sources, occurring around their respective mean depths. The individual deconvolved gravity effects thus separated out have been modelled using the sin x/x method by assuming a fluctuating interface between two formations. The applicability of the present method has been assessed using two observed Bouguer anomaly profiles: one from Ujjain to Mahan, and the other from Jhansi to Mandla where Deep Seismic Sounding (DSS) results are available. The proposed geological crustal models along these two profiles exhibit reasonably good agreement with those obtained from DSS results. A geologically plausible model of the crust in a virgin region has been presented along a Bouguer anomaly profile from Jaipur to Raipur. The following main conclusions have been drawn from the present analysis: (1) The depths to the Moho and Archaean basement interfaces fluctuate between 33.2 and 36.8 km and between 4.6 and 7.0 km respectively. (2) The Narmada-Son Lineament (NSL) does not coincide exactly with the Moho upwarp beneath it. However, this offset is greater in the eastern part of the NSL rather than in the western part. (3) The development of the Satpura horst structure is due to a rise in the Moho interface in a compressional regime. (4) The intrabasement feature (depth from 5 to 12 km) represents a hybrid massif possibly formed due to an admixture of sialic and simatic crust under a tensional regime in the Ujjain-Mahan section. 相似文献
18.
From our interpretation of the Bouguer gravity and aeromagnetic anomalies in south-east Scotland, we conclude that a massive granite batholith underlies the greater part of the eastern Southern Uplands. The granite model which we computed earlier from gravity anomalies in the Tweeddale area fits the observed magnetic anomalies closely, if a normal magnetization of 0.095 A m–1 is assigned, similar to values found for exposed local granites. Further gravity modelling shows that, apart from the Tweeddale boss, the granite shallows to less than 1 km near Lammer Law in East Lothian and extends north of the Lammermuir Fault. A model for the East Lothian volcanics was computed from their aeromagnetic anomalies, then their gravitational effect was combined with that estimated for the Devonian and Carboniferous sediments and the result stripped off the observed gravity field. The residual gravity anomalies were used to generate a two-dimensional model for the granite north of the Lammermuir Fault. The expected tectonic consequences of a massive granite batholith in the eastern Southern Uplands are compared with the known development of faults and sedimentary basins around its margins. 相似文献
19.
In this paper, on the basis of intensity data from 85 earthquakes occurred in China, the method of resolving overdetermined
equations by using the damped least squares method is applied to inversing for the mean value of 1 s. S wave quality factor,
the spreading factor and the S-wave acceleration at the foci of earthquakes in 7 regions of China. The relation between S-wave
acceleration at the foci of earthquakes and magnitude is discussed. As an example, 2-DQ
S distribution in Taiwan Province is obtained by inversion. It is found that there exists some corresponding relation between
this distribution and Bouguer gravitational anomaly and seismicity.
Preliminary analysis and discussion on results of the inversion, and estimation of error inQ
S are made.
The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,13, 202–211, 1991.
The English version of this paper is improved by Professor Yushou Xie. 相似文献
20.
The gravitational attraction produced by a geological body of irregular shape can be easily determined by dividing it into cubes of small size. The exact expression of the effect of a cube is very complicated, but it can be calculated by using an electronic computer. 4851 values of the gravitational attraction were determined for different positions of a cube with the side of 2l and the center in M(x0, y0, z0), for x0∈[0;20], y0∈[0;20] and z0∈[0;10]. Using these values, templates in double logarithmic representation were drawn, with x0 and z0 as parameters and y0 as abscissa, and with x0 and y0 as parameters and z0 in abscissa; this double set of templates permits a good interpolation for all cubes in the considered domain of M. The use of templates was tested to approximate the effect produced by a theoretical model of spherical shape and in a real case of a three-dimensional salt body of known shape based on a large number of boreholes. In both cases very good results were obtained. 相似文献