共查询到20条相似文献，搜索用时 46 毫秒
1.
E. LOINGER 《Geophysical Prospecting》1983,31(1):98-118
Variations of seismic interval velocities within the cable length cause anomalies in the stacking velocity analyses. Utilizing the approximation of rectilinear ray propagation, i.e. supposing that the velocity changes cause time delays only, it is shown that the stacking velocity anomalies are linearly related to the interval velocity variations. In particular, the stacking velocity anomaly is calculated when the interval velocity of an intermediate layer undergoes a stepwise variation. The amplitude of the anomaly increases with the ratio between horizon depth and cable length. From the forward model, a program for the inversion is derived in order to identify lateral changes of interval velocities from unsmoothed stacking velocity analyses. Some examples of the application of this technique to synthetic and real data are presented. 相似文献
2.
Michele Cercato 《Geophysical Prospecting》2011,59(2):210-226
Practical applications of surface wave inversion demand reliable inverted shear‐wave profiles and a rigorous assessment of the uncertainty associated to the inverted parameters. As a matter of fact, the surface wave inverse problem is severely affected by solution non‐uniqueness: the degree of non‐uniqueness is closely related to the complexity of the observed dispersion pattern and to the experimental inaccuracies in dispersion measurements. Moreover, inversion pitfalls may be connected to specific problems such as inadequate model parametrization and incorrect identification of the surface wave modes. Consequently, it is essential to tune the inversion problem to the specific dataset under examination to avoid unnecessary computations and possible misinterpretations. In the heuristic inversion algorithm presented in this paper, different types of model constraints can be easily introduced to bias constructively the solution towards realistic estimates of the 1D shear‐wave profile. This approach merges the advantages of global inversion, like the extended exploration of the parameter space and a theoretically rigorous assessment of the uncertainties on the inverted parameters, with the practical approach of Lagrange multipliers, which is often used in deterministic inversion, which helps inversion to converge towards models with desired properties (e.g., ‘smooth’ or ‘minimum norm' models). In addition, two different forward kernels can be alternatively selected for direct‐problem computations: either the conventional modal inversion or, instead, the direct minimization of the secular function, which allows the interpreter to avoid mode identification. A rigorous uncertainty assessment of the model parameters is performed by posterior covariance analysis on the accepted solutions and the modal superposition associated to the inverted models is investigated by full‐waveform modelling. This way, the interpreter has several tools to address the more probable sources of inversion pitfalls within the framework of a rigorous and well‐tested global inversion algorithm. The effectiveness and the versatility of this approach, as well as the impact of the interpreter's choices on the final solution and on its posterior uncertainty, are illustrated using both synthetic and real data. In the latter case, the inverted shear velocity profiles are blind compared with borehole data. 相似文献
3.
The geophysical data processor today has on offer a great variety of tools for the inversion of seismic reflection data to estimate geological structure. The major subset of these comprises migration procedures, which span a wide range of sophistication and cost in terms both of computation time and manual effort on the part of interpreters and processing staff. The choice of an over-powerful process can be very wasteful, but on the other hand too naive a migration procedure can lead to wrong interpretations which are much more costly still. Complete inversion procedures which aim to delineate all changes in rock densities and elastic properties in the subsurface are still in the imaginative stages of research. Not even the most sophisticated migration procedure in current use with real data, however, provides a complete inversion, but all depend in some measure on prior knowledge of the velocity structure of the section of the earth traversed by the seismic energy. Such knowledge may be very approximate at first, but each inversion should, through the skill of the interpreter, allow him to revise his velocity model and, up to some limit imposed by the quality and ambiguity of the original data, to improve the next inversion. Paradoxically, he can often be helped by using forward modeling procedures to check the implications of his ideas in the data domain, both in deciding how to update the velocity model and in selecting the most appropriate migration process to use next. We review here the currently available toolkit of migration and modeling processes and make suggestions as to how each process can fit into a learning strategy which can improve the interpretation as economically as possible and in as many iterative steps as the complexity of the earth's velocity structure makes necessary. An example is shown of the strategy being used in a complex overthrust region. The authors wish to thank the Chairman and Board of Directors of BP Exploration Co. for permission to publish this paper, and also make acknowledgment to our colleagues whose labours in research and development have made available to our use many of the essential tools required to implement the strategies we describe. 相似文献
4.
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
5.
We presented using the correlation coefficient of the analytic signal of real data and the analytic signal of synthetic data generated by the assumed source to estimate the structural index and the depth of the source. First, we assumed that the causative sources are located at different locations in the underground and the structural index of the assumed source is changed from 0 to 3, and then we separately compute the correlation coefficients of the analytic signal of the measured data and the analytic signal of the anomaly generated by each assumed source, the correlation coefficient can get the maximum value when the location and structural index of the assumed source are consistent with the real source. We tested the correlation coefficient method on synthetic noise-free and noise-corrupted magnetic anomalies, and the inversion results indicate that the new method can successfully finish the inversion of magnetic data. We also applied it to measured magnetic data, and we obtain the structural index and the location of the source. 相似文献
6.
In this paper we propose a 3D acoustic full waveform inversion algorithm in the Laplace domain. The partial differential equation for the 3D acoustic wave equation in the Laplace domain is reformulated as a linear system of algebraic equations using the finite element method and the resulting linear system is solved by a preconditioned conjugate gradient method. The numerical solutions obtained by our modelling algorithm are verified through a comparison with the corresponding analytical solutions and the appropriate dispersion analysis. In the Laplace‐domain waveform inversion, the logarithm of the Laplace transformed wavefields mainly contains long‐wavelength information about the underlying velocity model. As a result, the algorithm smoothes a small‐scale structure but roughly identifies large‐scale features within a certain depth determined by the range of offsets and Laplace damping constants employed. Our algorithm thus provides a useful complementary process to time‐ or frequency‐domain waveform inversion, which cannot recover a large‐scale structure when low‐frequency signals are weak or absent. The algorithm is demonstrated on a synthetic example: the SEG/EAGE 3D salt‐dome model. The numerical test is limited to a Laplace‐domain synthetic data set for the inversion. In order to verify the usefulness of the inverted velocity model, we perform the 3D reverse time migration. The migration results show that our inversion results can be used as an initial model for the subsequent high‐resolution waveform inversion. Further studies are needed to perform the inversion using time‐domain synthetic data with noise or real data, thereby investigating robustness to noise. 相似文献
7.
如何快速、精确地利用叠前深度偏移进行偏移速度分析是勘探地震学的一项重要研究内容,针对该问题,本文提出一种二阶精度广义非线性全局最优的偏移速度反演方法。我们将首先去掉速度模型修正量与成象深度差呈线性关系的假设,推导出具有二阶精度的速度模型修正量计算公式,使每一次迭代得到的速度模型尽可能地接近实际模型;然后采用广义非线性反演方法反演获得对所有道集的全局最优的速度模型修正量,不仅极大地加快了收敛速度,而且反演过程中陷入局部极小的可能性也减小了。理论模型和Marmousi模型的处理结果表明:本方法精度高、处理速度快,提高了偏移速度分析方法的实用性和对复杂构造成像的准确性。 相似文献
8.
电阻率法和背景噪声法是通过获得地下介质的电阻率和速度参数的分布来探究地球内部物质分布的非均匀性特征,联合反演可以有效地发挥两种方法的优势,减小反演多解性.本文采用有限内存拟牛顿（L-BFGS）算法实现了电阻率法和背景噪声法的单方法三维反演,然后基于电阻率和速度模型结构耦合约束,采用交替迭代方式实现了电阻率法和背景噪声法的三维联合反演.通过设计规则体组合模型和不规则体组合模型进行理论模型合成数据三维反演试算,结果表明：联合反演可以获得同时满足数据拟合差和结构更为相似的速度-电阻率模型;联合反演可以压制背景噪声单方法反演出现的假异常,获得更精细的速度结构;联合反演获得的电阻率模型对倾斜异常体、高阻覆层下方异常体、圈闭的高/低阻体等边界信息有明显的提升,有效克服电阻率法单方法反演的局限,提高深部电阻率的分辨率. 相似文献
9.
Leonardo Azevedo Rúben Nunes Amílcar Soares Guenther Schwedersky Neto Teresa S. Martins 《Geophysical Prospecting》2018,66(Z1):116-131
Seismic inversion plays an important role in reservoir modelling and characterisation due to its potential for assessing the spatial distribution of the sub‐surface petro‐elastic properties. Seismic amplitude‐versus‐angle inversion methodologies allow to retrieve P‐wave and S‐wave velocities and density individually allowing a better characterisation of existing litho‐fluid facies. We present an iterative geostatistical seismic amplitude‐versus‐angle inversion algorithm that inverts pre‐stack seismic data, sorted by angle gather, directly for: density; P‐wave; and S‐wave velocity models. The proposed iterative geostatistical inverse procedure is based on the use of stochastic sequential simulation and co‐simulation algorithms as the perturbation technique of the model parametre space; and the use of a genetic algorithm as a global optimiser to make the simulated elastic models converge from iteration to iteration. All the elastic models simulated during the iterative procedure honour the marginal prior distributions of P‐wave velocity, S‐wave velocity and density estimated from the available well‐log data, and the corresponding joint distributions between density versus P‐wave velocity and P‐wave versus S‐wave velocity. We successfully tested and implemented the proposed inversion procedure on a pre‐stack synthetic dataset, built from a real reservoir, and on a real pre‐stack seismic dataset acquired over a deep‐water gas reservoir. In both cases the results show a good convergence between real and synthetic seismic and reliable high‐resolution elastic sub‐surface Earth models. 相似文献
10.
为了有效解决目前大地电磁和地震走时资料单方法反演结果一致性不好的问题,同时克服基于岩石不同物性参数间关系耦合约束联合反演的局限性,本文研究了基于交叉梯度耦合约束的大地电磁与地震走时资料的三维联合反演算法.以较为成熟的天然地震走时资料三维正反演和大地电磁三维正反演算法为基础,实现了具有共同的反演网格,以交叉梯度结构耦合约束,并能同时获得电阻率和速度模型的三维联合反演算法.分别利用单棱柱体模型和双棱柱体模型合成数据进行了联合反演试算.结果表明:无论是单棱柱体模型还是双棱柱体模型,联合反演结果比单独反演对异常体的空间形态都有更好的恢复,其中单棱柱体模型反演的异常体电阻率更接近于真实电阻率,双棱柱体模型的联合反演结果不仅消除了围岩的部分电阻率假异常,而且增强了对异常体深部速度结构特征的恢复程度.联合反演还能同时改善电阻率和速度反向变化异常体的单独反演结果,进一步证明交叉梯度耦合不依赖于岩石物性关系,而强调地下结构的相似性,具有更普遍的适用性. 相似文献
11.
Merging active and passive data sets in traveltime tomography: The case study of Campi Flegrei caldera (Southern Italy) 总被引：1，自引：0，他引：1
Jean Battaglia Aldo Zollo Jean Virieux Dario Dello Iacono 《Geophysical Prospecting》2008,56(4):555-573
We propose a strategy for merging both active and passive data sets in linearized tomographic inversion. We illustrate this in the reconstruction of 3D images of a complex volcanic structure, the Campi Flegrei caldera, located in the vicinity of the city of Naples, southern Italy. The caldera is occasionally the site of significant unrests characterized by large ground uplifts and seismicity. The P and S velocity models of the caldera structure are obtained by a tomographic inversion based on travel times recorded during two distinct experiments. The first data set is composed of 606 earthquakes recorded in 1984 and the second set is composed of recordings for 1528 shots produced during the SERAPIS experiment in 2001. The tomographic inversion is performed using an improved method based on an accurate finite‐difference traveltime computation and a simultaneous inversion of both velocity models and earthquake locations. In order to determine the adequate inversion parameters and relative data weighting factors, we perform massive synthetic simulations allowing one to merge the two types of data optimally. The proper merging provides high resolution velocity models, which allow one to reliably retrieve velocity anomalies over a large part of the tomography area. The obtained images confirm the presence of a high P velocity ring in the southern part of the bay of Pozzuoli and extends its trace inland as compared to previous results. This annular anomaly represents the buried trace of the rim of the Campi Flegrei caldera. Its shape at 1.5 km depth is in good agreement with the location of hydrothermalized lava inferred by gravimetric data modelling. The Vp/Vs model confirms the presence of two characteristic features. At about 1 km depth a very high Vp/Vs anomaly is observed below the town of Pozzuoli and is interpreted as due to the presence of rocks that contain fluids in the liquid phase. A low Vp/Vs body extending at about 3–4 km depth below a large part of the caldera is interpreted as the top of formations that are enriched in gas under supercritical conditions. 相似文献
12.
João B.C. Silva Darcicléa F. Santos Daniele P. Monteiro 《Geophysical Prospecting》2020,68(3):1057-1071
We advance a principle directed to assigning numerical values to free parameters usually present in inversion methods. It may be formulated as: ‘Optimum estimates of free parameters in an inversion procedure must lead, in tests using synthetic data, to solutions whose geometrical expression reflects the main qualitative or semiquantitative geological characteristic of the study area.’ To this end, the interpreter should (i) specify a typical anomalous source geometry which incorporates the most relevant geological information for the study area, (ii) compute the corresponding gravity anomaly and (iii) invert the anomaly for the source geometry finding the numerical values of the free parameters that lead to a solution closest to the typical source. Application of the above methodology to synthetic and real data from the basement relief of a rift basin has asserted its efficacy. 相似文献
13.
Migration velocity analysis and waveform inversion 总被引：3，自引：0，他引：3
William W. Symes 《Geophysical Prospecting》2008,56(6):765-790
Least‐squares inversion of seismic reflection waveform data can reconstruct remarkably detailed models of subsurface structure and take into account essentially any physics of seismic wave propagation that can be modelled. However, the waveform inversion objective has many spurious local minima, hence convergence of descent methods (mandatory because of problem size) to useful Earth models requires accurate initial estimates of long‐scale velocity structure. Migration velocity analysis, on the other hand, is capable of correcting substantially erroneous initial estimates of velocity at long scales. Migration velocity analysis is based on prestack depth migration, which is in turn based on linearized acoustic modelling (Born or single‐scattering approximation). Two major variants of prestack depth migration, using binning of surface data and Claerbout's survey‐sinking concept respectively, are in widespread use. Each type of prestack migration produces an image volume depending on redundant parameters and supplies a condition on the image volume, which expresses consistency between data and velocity model and is hence a basis for velocity analysis. The survey‐sinking (depth‐oriented) approach to prestack migration is less subject to kinematic artefacts than is the binning‐based (surface‐oriented) approach. Because kinematic artefacts strongly violate the consistency or semblance conditions, this observation suggests that velocity analysis based on depth‐oriented prestack migration may be more appropriate in kinematically complex areas. Appropriate choice of objective (differential semblance) turns either form of migration velocity analysis into an optimization problem, for which Newton‐like methods exhibit little tendency to stagnate at nonglobal minima. The extended modelling concept links migration velocity analysis to the apparently unrelated waveform inversion approach to estimation of Earth structure: from this point of view, migration velocity analysis is a solution method for the linearized waveform inversion problem. Extended modelling also provides a basis for a nonlinear generalization of migration velocity analysis. Preliminary numerical evidence suggests a new approach to nonlinear waveform inversion, which may combine the global convergence of velocity analysis with the physical fidelity of model‐based data fitting. 相似文献
14.
为了降低单一地球物理方法反演的多解性及受噪声的影响程度,本文围绕重力、磁法和大地电磁法开展了三维联合反演的研究.重、磁采用基于对数障碍法的正则化反演算法,大地电磁使用limited-memory BroydenFletcher-Goldfarb-Shanno(L-BFGS)反演算法,引入交叉梯度函数实现了三种物性结构的相互耦合,最终开发出一套重磁电三维联合反演算法,并实现MPI并行加速计算.通过理论模型算例验证了算法的准确性,结果表明:不论是单棱柱体模型还是组合棱柱体模型,联合反演结果相较单独反演对于异常体的空间形态刻画以及物性数值恢复具有较好的提升;单棱柱体模型算例使得异常体的物性参数(密度、磁化率和电阻率)更加接近于真实的物性参数;组合棱柱体模型的联合反演结果不仅仅消除了围岩物性参数的假异常,而且还增强了异常体边界结构的恢复程度. 相似文献
15.
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
16.
17.
The estimation of uncertainty for any geophysical model is important for determining how reliable the model is. It is especially important for subjective trial and error modelling techniques like forward ray-tracing modelling of wide-angle seismic data when the final result is very dependent on the interpreter’s knowledge of the area and experience. In this kind of modelling, it is common to encounter over interpretation of the seismic data without checking the uncertainty of the result, especially in the deep parts that are not constrained with other a priori knowledge. In this paper, we propose a method of estimating the uncertainty of the final models based on a one dimensional method of small error propagation generalized for 2D profiles. With a simple approximation, we estimate the uncertainty for published interpretative models of selected profiles from seismic experiments in the Central Europe. We conclude that for typical wide angle seismic profiles we can reliably interpret four layered models of the Earth’s crust based on traveltimes fitting. We also show how the number of layers influence obtained uncertainties. Estimated uncertainties for both the velocity fields and the boundaries between layers are important for future tectonic and geodynamic interpretation of those profiles. 相似文献
18.
面波成像是研究地壳上地幔横波速度结构的一种重要方法．通常,面波相速度或群速度成像假设面波沿大圆路径传播．但是,在地下介质速度结构变化较大时,面波会偏离大圆路径传播,从而导致基于大圆路径假设下的面波成像结果存在一定的误差. 我们采用基于射线追踪的面波成像方法,研究了面波的偏离大圆路径传播对四川西部地区面波相速度成像结果的影响．使用快速行进法(fast marching method)进行面波传播路径的射线追踪,采用子空间反演法(subspace inversion)进行迭代反演,对理论模型合成数据和川西台阵的短周期背景噪声相速度频散数据进行成像分析,并与使用大圆路径传播的成像结果进行对比．对理论模型的测试结果表明,当速度结构变化较大时,基于偏离大圆路径传播的面波成像能够更好地恢复模型异常．对川西台阵的真实数据反演结果显示:在短周期为6 s时,基于偏离大圆路径传播的反演方法较基于大圆路径传播的反演方法所获得的相速度异常的幅度更大些,在四川盆地区域两者的差异接近0.2 km/s;在周期为10 s时,两种反演方法的差异显著减小,基本都在0.1 km/s以内．这主要是因为6 s周期的面波相速度对复杂的上地壳浅层结构更为敏感,从而使得面波的偏离大圆路径传播效应对反演结果的影响更为显著．本文结果表明,当某一周期不同路径的面波相速度测量值变化较大,例如相对于平均相速度的异常超过10％时,则需考虑采用基于偏离大圆路径传播的面波成像方法,否则速度异常较大区域的反演结果可能会造成较大的偏差． 相似文献
19.
In the case of 3D multilayered structures the 2D interval velocity analysis may be inaccurate. This fact is illustrated by synthetic examples. The method proposed solves the 3D inverse problem within the scope of the ray approach. The solution, i.e. the interval velocities and the reflection interface position, is obtained using data from conventional 2D line profiles arbitrarily located and from normal incidence time maps. Although the input information is essentially limited, the method presented reveals only minor biased velocity estimates. In order to implement the proposed 3D inversion method, we developed a processing procedure. The procedure performs the evaluation of reflection time and ray parameters along line profiles, 3D interval velocity estimation, and time-to-depth map migration. Tools to stabilize the 3D inversion are investigated. The application of the 3D inversion technique to synthetic and real data is compared with results of the 2D inversion. 相似文献