共查询到20条相似文献，搜索用时 894 毫秒
1.
H. GRANSER 《Geophysical Prospecting》1987,35(9):1030-1041
In mapping the topography of the basement of deep sedimentary basins by gravity modelling, the accuracy can be improved by incorporating an exponential increase in density with depth. For calculating the gravity effect of a three-dimensional (3D) structure with such an exponential density-depth relation a frequency-domain forward algorithm based on series expansion is presented, the numerical evaluation of which can be performed efficiently by fast Fourier transform. The algorithm can be applied in a recursive procedure to give the inverse solution in terms of basement relief. The inversion procedure is satisfactorily tested on a 2D synthetic example and a 3D field example of gravity data from the western margin of the Pannonian Basin in eastern Austria, where up to 2.2 km of Tertiary sediments overlie an igneous or metamorphic basement. The results are confirmed by basement intersections in several wells. 相似文献
2.
3.
R.E. Chvez E.L. Flores J.O. Campos M. Ladrn de Guevara M.C. Fernndez‐Puga J. Herrera 《Geophysical Prospecting》2000,48(5):835-870
A comprehensive reinterpretation of the available gravity, magnetic, geothermal, geological and borehole information has been made of the Laguna Salada Basin to establish a 3D model of the basement and sedimentary infill. According to statistical spectral analysis, the residual gravity anomaly is due to sources with a mean regional depth of 2.8 km. The topography of the basement was obtained from a three‐dimensional inversion carried out in the wavenumber domain using an iterative scheme. The maximum density contrast of ?300 kg/m3 estimated from previous studies and the mean depth of 2.5 km finally constrained this inversion. The resulting model indicated that the sedimentary infill is up to 4.2 km thick at its deepest point. According to the gravity‐derived basement topography, the basin presents an asymmetry (i.e. it is of the half‐graben type). It is deeper to the east, where it is delimited from the Sierra Cucapah by a step fault. By contrast, the limit with the Sierra de Juarez is a gently sloping fault (i.e. a listric fault). The basement is not even, but it comprises a series of structural highs and lows. N–S to NW–SE and E–W to NE–SW faults delimit these structural units. The magnetic modelling was constrained by (i) the gravity‐derived basement topography; (ii) a Curie isotherm assumed to be between 7 km and 10 km; (iii) assuming induced magnetization only; (iv) the available geological and borehole information. The magnetic anomalies were interpreted successfully using the gravity‐derived basement/sedimentary interface as the top of the magnetic bodies (i.e. the magnetic modelling supports the gravity basement topography). An elongated N–S to NW–SE trending highly magnetized body running from south to north along the basin is observed to the west of the basin. This magnetic anomaly has no gravity signature. Such a feature can be interpreted as an intrusive body emplaced along a fault running through the Laguna Salada Basin. Treatment of the gravity and magnetic information (and of their horizontal gradients) with satellite image processing techniques highlighted lineaments on the basement gravity topography correlating with mapped faults. Based on all this information, we derived detailed geological models along four selected profiles to simulate numerically the heat and fluid flow in the basin. We used a finite‐difference scheme to solve the coupled Darcy and Fourier differential equations. According to our results, we have fluid flow in the sedimentary layers and a redistribution of heat flow from the basin axis toward its rims (Sierra de Juárez and Sierra Cucapah). Our model temperatures agree within an error of 4% with the observed temperature profiles measured at boreholes. Our heat‐flow determinations agree within an error of ±15% with extrapolated observations. The numerical and chemical analyses support the hypothesis of fluid circulation between the clay–lutite layer and the fractured granitic basement. Thermal modelling shows low heat‐flow values along the Laguna Salada Basin. Deep fluid circulation patterns were observed that redistribute such flow at depth. Two patterns were distinguished. One displays the heat flow increasing from the basin axis towards its borders (temperature increase of 20°C). The second pattern shows an increasing heat flow from south to north of the basin. Such behaviour is confirmed by the temperature measurements in the thermometric boreholes. 相似文献
4.
Parabolic density function in sedimentary basin modelling 总被引：1，自引：0，他引：1
For modelling sedimentary basins of large thickness from their gravity anomalies, the concept of parabolic density function which explains the variation of true density contrast of the sediments with depth in such basins is introduced inBott's (1960) procedure. The analytical expression the gravity anomaly of a two-dimensional vertical prism with parabolic density contrast needed to estimate the gravity effect of the basin in modelling procedure is derived in a closed form. Two profiles of gravity anomalies, one across San Jacinto Graben, California and the other across Tucson basin, Arizona where the density of sediments is found to vary with depth are interpreted. 相似文献
5.
区域重力异常蕴含丰富的断裂构造特征信息.采用小波多尺度分解、归一化总水平导数垂向导数(NVDR_THDR)和剖面2.5D重力异常反演方法对北京平原区高精度区域重力资料进行了处理,获得了主要断裂构造平面位置、长度、规模、汇交关系及深浅延伸特征,分析了利用重力异常识别断裂的效果.结果表明:(1)北京平原区NE向断裂平面延展长度大、连续性强,NW向断裂分段性明显,连续性弱,但NW向断裂对NE向断裂有切割改造迹象.近EW或SN向断裂分布较为局限.(2)主控断裂平面和垂向延伸特征差异明显,顺义断裂、孙河断裂、永定河断裂等为盖层断裂;南口断裂、孙河断裂西段、二十里长山断裂和张喜庄断裂为基底断裂;黄庄—高丽营断裂南段、南苑—通县断裂、礼贤断裂、夏垫断裂和皮各庄断裂东段为地壳断裂.(3)利用NVDR_THDR峰值异常带的连续性、幅值、宽度及错切关系可有效识别断裂的平面展布特征,通过小波变换获得的不同深度等效层异常结合2.5D剖面反演可有效研究断裂在基岩内部的深浅延伸情况,但重力异常的垂向分辨能力弱,断裂在新生界内部延伸特征需结合其他地质资料进一步分析. 相似文献
6.
Global ellipsoid-referenced topographic,bathymetric and stripping corrections to gravity disturbance
This paper revisits several aspects of defining and computing the anomalous gravity data for purposes of gravimetric inversion/interpretation.
Attention is paid to evaluation of a refined global topographic correction to the gravity disturbance based on the reference
ellipsoid (RE) and constant reference density for solid topography onshore and sea water density for liquid topography offshore.
The global bathymetric correction is discussed. Two issues associated with compilation and inversion of bathymetrically and
topographically corrected gravity disturbances in regions of negative ellipsoidal (geodetic) heights are pointed out: the
evaluation of normal gravity and the harmonic continuation of the gravity data. Stripping, the removal of an effect of a known
density contrast, is considered also for additional geological elements such as lakes, glaciers, sedimentary basins, isostatic
mountain roots, etc. The stripping corrections are discussed in the context of the gravimetric inverse problem. 相似文献
7.
An automatic inversion using ridge regression algorithm is developed in the space domain to analyze the gravity anomalies of sedimentary basins, among which the density contrast decreases with depth following a prescribed exponential function. A stack of vertical prisms having equal widths, whose depths become the unknown parameters to be estimated, describes the geometry of a sedimentary basin above the basement complex. Because no closed form analytical equation can be derivable in the space domain using the exponential density-depth function, a combination of analytical and numerical approaches is used to realize forward gravity modeling. The depth estimates of sediment-basement interface are initiated and subsequently improved iteratively by minimizing the objective function between the observed and modeled gravity anomalies within the specified convergence criteria. Two gravity anomaly profiles, one synthetic and a real, are interpreted using the proposed technique to demonstrate its applicability. 相似文献
8.
The decrease of density contrast in sedimentary basins may be approximated by a quadratic function. A sedimentary basin may be viewed as a number of prisms placed in juxtaposition. Equations in closed form for the gravity anomalies of 3D and 2½ D prismatic models are derived. Approximate equations for these models are also derived for rapid calculations. Efficient methods are developed for anomaly calculation by an appropriate use of the exact and approximate equations, and hence, for 3D and 2½ D modelling. The depths to the basement are adjusted iteratively by comparing the calculated anomalies with the observed anomalies. These methods are applied for analysis of the residual anomaly map of the Los Angeles Basin, California. 相似文献
9.
We present an inversion technique based on the Marquardt algorithm to estimate the depth of a 2.5-D sedimentary basin in addition
to the regional gravity anomaly that is associated with the residual gravity anomaly, wherein the density contrast varies
parabolically with depth. Forward modeling is carried out through a derived analytical gravity expression of a 2.5-D vertical
prism. Inversion of a theoretical gravity anomaly with and without a regional gravity anomaly illustrates the procedure that
it is found to be insensitive to the regional gravity effect. Furthermore, the algorithm is exemplified with the gravity anomalies
of the derived density-depth model of the Godavari subbasin, India with a parabolic density profile resulting in a more consistent
geological model rather than a constant density profile. The main advantage of this method is that it works well even when
the profile of interpretation does not bisect the strike length of the sedimentary basin. 相似文献
10.
Parameter optimization of gravity density inversion based on correlation searching and the golden section algorithm 总被引：1，自引：0，他引：1
For density inversion of gravity anomaly data, once the inversion method is determined, the main factors affecting the inversion result are the inversion parameters and subdivision scheme. A set of reasonable inversion parameters and subdivision scheme can, not only improve the inversion process efficiency, but also ensure inversion result accuracy. The gravity inversion method based on correlation searching and the golden section algorithm is an effective potential field inversion method. It can be used to invert 2D and 3D physical properties with potential data observed on flat or rough surfaces. In this paper, we introduce in detail the density inversion principles based on correlation searching and the golden section algorithm. Considering that the gold section algorithm is not globally optimized, we present a heuristic method to ensure the inversion result is globally optimized. With a series of model tests, we systematically compare and analyze the inversion result efficiency and accuracy with different parameters. Based on the model test results, we conclude the selection principles for each inversion parameter with which the inversion accuracy can be obviously improved. 相似文献
11.
本文利用三个高阶重力场模型LP150Q、GLGM-3和SGM150j以及嫦娥地形模型CLTM-s01,在频率域内使用固定窗口的方法,研究了不同重力场模型的重力/地形局部导纳谱与局部相关谱的全球分布,以及典型质量瘤盆地重力/地形局部导纳谱与局部相关谱分布的特征.结果表明:加入远月面重力场信息有助于增强重力场模型在中高频段的信号强度;三个重力场模型LP150Q、GLGM-3和SGM150j均适合于作近月面重力/地形局部导纳与局部相关性的分析和近月面地球物理参数的估计;重力场模型LP150Q和GLGM-3较适合作远月面大范围的研究,不适合于作远月面重力/地形局部导纳谱与局部相关谱的分析以及作远月面局部区域地球物理参数的估计,SGM150j较适合于作远月面局部区域地球物理参数的估计;近月面大型质量瘤盆地异常质量的尺度比远月面质量瘤盆地异常质量的大,而深度也比远月面的深. 相似文献
12.
V. Chakravarthi 《Pure and Applied Geophysics》1995,145(2):327-335
The decrease in density contrast of sedimentary rocks with depth in many sedimentary basins can be approximated by a parabolic density function. Analytical gravity expression of an outcropping two-dimensional vertical step along which the density contrast decreases parabolically with depth is derived in the space domain. A modification ofBott's (1960) method of gravity interpretation is proposed by considering two outcropping vertical steps on either side of the first and last observation points in addition toN outcropping vertical prisms in order to interpret the gravity anomalies of nonoutcropping basins. The thicknesses of the two outcropping vertical steps are made equal to the thicknesses of the two outcropping vertical prisms placed below the first and last observation points. The initial depth estimates of the sedimentary basin are calculated by the infinite slab formula ofVisweswara Rao
et al. (1993). The gravity effects of theN outcropping prisms and the two outcropping vertical steps are calculated at each anomaly point and the depth to the floor of the basin are adjusted based on the differences between the observed and calculated anomalies. A gravity anomaly profile of Los Angeles basin, California is interpreted. 相似文献
13.
An algorithm to calculate the gravity anomaly of sedimentary basins with exponential density-depth relationships 总被引：2，自引：0，他引：2
We derive wavenumber domain expressions to calculate the gravity anomaly of a body with irregular bounding surfaces and an exponential density‐depth relationship. We apply the method to sedimentary basins, which commonly have this type of geometry and density distribution. The mathematical formulation also allows the exponential density‐depth relationship to be measured from an arbitrary irregular surface rather than the top surface. Using this arrangement, the gravity anomaly of exhumed sedimentary basins can be predicted if the amount of eroded section can be estimated. The corresponding inverse algorithms are also derived. Examples of the use of the forward algorithms, from the Galicia Interior Basin and the Central Irish Sea Basin, are used to illustrate these methods. 相似文献
14.
讨论了利用面波与布格重力异常联合反演三维地壳速度结构的新方法,并利用该方法联合反演获得山西断陷带地壳S波速度结构.通过建立速度与密度之间的经验关系,利用非线性迭代反演方法获得最终速度模型.结果显示,联合反演获得的速度模型可以同时提高对面波及重力数据的观测拟合程度,而面波单独反演得到的速度模型则无法很好的拟合重力观测数据.相比较,联合反演速度模型中的大同火山区中下地壳的低速异常幅值小于面波单独反演模型中低速异常体的幅值.联合反演速度模型结果揭示,吕梁山地区在中下地壳存在低速异常,并且和北部的大同火山区低速异常相连接,说明可能导致新生代以来大同火山区岩浆活动的上地幔构造活动(上地幔局部上涌,地幔柱)可能对山西断陷带的形成和构造活动起到了一定的控制作用,并且导致了吕梁山地区中下地壳的低速异常. 相似文献
15.
以活动论构造历史观为指导进行渤海海域残留盆地宏观分布特征研究. 以岩石物性为基础建立地质界面与物性界面的联系，通过重、磁、震等方法组合圈画不同物性界面的分布特征. 浅层沉积盆地结构通过反射地震资料控制，深层地质结构信息利用重磁异常场分离、物性界面反演等方法得到. 在地层分布格架基础上分析前新生代残留盆地宏观分布范围. 并结合渤海海域实例研究介绍了残留盆地宏观分布研究的技术方法和流程，在计算上古生界-中生界及元古界-下古生界残余地层厚度的基础上给出了渤海海域残留盆地的宏观分布范围，并指出在歧口凹陷东南部、石臼坨隆起南部及东北部、渤南凸起南部、辽东湾等地区是较好的前新生代油气潜力区. 相似文献
16.
An inversion technique using the Marquardt optimization is developed to interpret the gravity anomalies due to anticlinal and synclinal structures with density contrast varying continuously with depth. The algorithm simultaneously estimates the parameters of the respective models, in addition to the regional gravity background that is invariably associated with the residual gravity anomaly. Forward modelling is realized through analytically derived gravity expressions for the respective models in the space domain. The efficacy of the inversion is demonstrated with the gravity anomaly due to a theoretical model, in each case with and without the regional background. In addition, the applicability is illustrated using the gravity anomalies of the Pays De Bray anticline, situated north‐west of Paris, France. The interpreted depth of the Pays De Bray anticline using the present inversion compares well with the drilling depth. 相似文献
17.
针对重力异常反演的现状,采用矩形单元体网格剖分的二度半体组合模型,模拟任意的多层密度界面或形体,实现了重力正演.该建模方法适应性强,适合于实际工作中常见的密度横向变化的复杂模型.使用改进的全局寻优的快速模拟退火算法,对重力异常进行反演,结合这种灵活的密度建模方法,反演过程中只需要反演各矩形单元体的密度参数,即可同时得到地质体的界面或形态以及密度值分布.通过复杂界面和形体的模型试验,证明了方法的效果.在江苏下扬子地质构造复杂区的实际应用说明,在地震等先验信息约束下,该重力反演方法提高了反演精度并减少了多解性,可有效解决古生界泥盆系-志留系目的层分布等地质问题. 相似文献
18.
Giovanna Berrino Gennaro Corrado Umberto Riccardi 《Journal of Volcanology and Geothermal Research》2008
Bathymetric and gravity surveys were carried out from 1988 to 1994, in the Gulf of Naples (Southern Italy) to offshore extend the already existing Bouguer anomaly map. In order to improve the knowledge of the structural setting beneath the active Neapolitan volcanoes (Vesuvio, Campi Flegrei and Ischia), 862 stations were surveyed within the isobath of 400 m; at the same time, and about 2000 on-land gravity values were also collected. A new Bouguer anomaly map spanning the whole volcanic region was drawn from the final data set. Gravity anomalies were referred to the new absolute gravity station in Naples and computed according to 1980 Geodetic Reference System. Finally, a density value of 2200 kg/m3 was used in the computation of the Bouguer and terrain effects. We carried out the inversion of the gravity anomalies adopting a 2.5-D modelling along selected profiles crossing the investigated area. The interpretative models were constrained to data obtained from deep wells and other geophysical investigations. 相似文献
19.
Multi‐block finite‐difference method for 3D elastodynamic simulations in anisotropic subhorizontally layered media 
下载免费PDF全文
下载免费PDF全文 Prediction of elastic full wavefields is required for reverse time migration, full waveform inversion, borehole seismology, seismic modelling, etc. We propose a novel algorithm to solve the Navier wave equation, which is based on multi‐block methodology for high‐order finite‐difference schemes on curvilinear grids. In the current implementation, the blocks are subhorizontal layers. Smooth anisotropic heterogeneous media in each layer can have strong discontinuities at the interfaces. A curvilinear adaptive hexahedral grid in blocks is generated by mapping the original 3D physical domain onto a parametric cube with horizontal layers and interfaces. These interfaces correspond to the main curvilinear physical contrast interfaces of a subhorizontally layered formation. The top boundary of the parametric cube handles the land surface with smooth topography. Free‐surface and solid–solid transmission boundary conditions at interfaces are approximated with the second‐order accuracy. Smooth media in the layers are approximated up to sixth‐order spatial schemes. All expected properties of the developed algorithm are demonstrated in numerical tests using corresponding parallel message passing interface code. 相似文献