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1.
The interpretation protocols for defining offshore rifted margin architecture normally include seismic‐reflection analysis supplemented by refraction and/or potential field modelling to help constrain sedimentary, basement and Moho geometries at depth and/or the presence of magmatic material. Interpretation of modern high‐resolution long‐offset reflection profiles shows that significant mismatches may arise between the structural observations made from these data and the common translation of density, magnetic or velocity values into specific rock types made by geophysical models. We illustrate this problem with three examples from the Mid‐Norwegian rifted system, and discuss the implications with respect to the geological interpretation. 相似文献
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Seawater intrusion (SWI) is a complex process, where 3D modeling is often necessary in order to monitor and manage the affected aquifers. Here, we present a synthetic study to test a joint hydrogeophysical inversion approach aimed at solving the inverse problem of estimating initial and current saltwater distribution. First, we use a 3D groundwater model for variable density flow based on discretized flow and solute mass balance equations. In addition to the groundwater model, a 3D geophysical model was developed for direct current resistivity imaging and inversion. The objective function of the coupled problem consists of data misfit and regularization terms as well as a coupling term that relates groundwater and geophysical states. We present a novel approach to solve the inverse problem using an alternating direction method of multipliers (ADMM) to minimize this coupled objective function. ADMM enables to treat the groundwater and geophysical part separately and thus use the existing software with minor changes. To further reduce the computational cost, the sensitivities are derived analytically for the discretized system of equations, which allows us to efficiently compute the gradients in the minimization procedure. The method was tested on different synthetic scenarios with groundwater and geophysical data represented by solute mass fraction data and direct current resistivity data. With the ADMM approach, we were able to obtain better estimates for the solute distribution compared to just considering each data separately, solving the problem with a simple coupled approach or by a direct substitution of the coupling constraint. 相似文献
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“构造变形岩相”填图方法的创立和应用为老矿区深部及外围的找矿工作指明了方向,在实践中取得了显著的效果,需要大力推广和深入研究。对于构造变形岩相带的深部结构认识,需要依靠地球物理信息的解译。与地球物理场性质相类似,构造变形岩相带也是一个现存的地质体;物探工作目的是要探测和揭示构造变形岩相带的埋深、轮廓、内部结构构造等特征,为确定其形成时间和演化过程提供依据。由于地质与地球物理的复杂时空关系,如果仅以新鲜岩石标本物性参数的差异作为判别标志,难以提高地球物理方法的分辨率和有效性。结合构造变形岩相进行综合解译,更能提高解释推断成果的多学科融合性。作为终极勘探目标,需要紧密结合构造控矿级序,建立构造变形岩相带的三级分类标准,提取对应的地球物理信息:一级构造变形岩相带为目标物所处的构造单元及构造应力场,及其所对应的区域地球物理场特征,如隆凹构造相间的伸展构造域;二级构造变形岩相带为目标物所处的控矿构造体系,及其所对应的矿田地球物理场特征,如岩浆核杂岩隆起-拆离构造系统;三级构造变形岩相带为目标物所在的有利成矿构造部位,及其所对应于关键剖面的地球物理特征,如侵入岩体与围岩的接触带或者含矿断裂带等。选择国际流行的典型金属矿床类型,介绍了三级构造变形岩相带的地球物理组合信息特征及其分级利用操作流程,为有效应用地球物理勘探方法开展深部找矿预测提供了范例。 相似文献
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岩土参数的空间变异性分析 总被引：4，自引：0，他引：4
岩土参数具有空间变异性和不确定性,本文将岩土参数视为具有随机性和结构性的区域化变量,利用区域化变量理论和地质统计方法分析上海地基土有代表性的抗剪强度指标的空间变异特性。结果表明该方法是可行的。 相似文献
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文中以甘肃北山花岗岩中发育的构造裂隙(主要指节理尺度)为研究对象,应用地质统计分析理论,以裂隙面密度P21 作为地质统计分析的区域性变量,探索花岗岩岩体裂隙空间分布模式。结果表明:甘肃北山芨芨槽候选场址区域内花岗岩岩体裂隙空间分布具有明显的各向异性特征,变异主轴方向明显; 变异主轴区域内的裂隙分组地质统计特征显示,区域内第1分组裂隙并非是传统意义上的均匀随机分布,而是具有明显的空穴效应特征,应该在三维裂隙网络建模工作中予以考虑。本文在考虑本组裂隙空穴效应特征基础上,针对三维裂隙网络建模方法提出了新的建议。 相似文献
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蟒岭地区西部地处秦岭腹心,位于不同构造单位结合处,构造变动剧烈,岩浆活动频繁,多数矿产与中酸性岩体息息相关。综合物探工作通过地面高精度磁测、激发极化法和高精度重力测量三种地球物理综合测量方法,开展了研究区的磁场、重力场、极化率和电阻率的分布特征研究。深入分析了地质和地球物理特征的异同,并结合物性工作总结了中酸性岩体与地层的差异,了解了深部隐伏岩体的信息,圈定了岩体在地表的位置,推断出地下深层空间的地质结构,为进一步查找岩体以及其他与之有关的工程勘查活动提供借鉴,为该地区及类似地质背景下隐伏岩体定位预测提供了可靠的方法。 相似文献
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From a gravitational field analysis, the lithosphere was regionalized and a structural schematic map of the eastern part of the Indian Ocean was compiled. The area adjacent to the western margin of Australia was studied. The region is characterized by a complex lithospheric structure. It includes heterogeneous blocks of varying age, framed by structures with different morphological and geophysical expression and varying genesis. To clarify the peculiarities of tectonic structures of various genetic types, structural-density modeling was performed. This made it possible to establish certain gravimetric indicators characteristic of structures of various genesis. 相似文献
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A Bayesian linear inversion methodology based on Gaussian mixture models and its application to geophysical inverse problems are presented in this paper. The proposed inverse method is based on a Bayesian approach under the assumptions of a Gaussian mixture random field for the prior model and a Gaussian linear likelihood function. The model for the latent discrete variable is defined to be a stationary first-order Markov chain. In this approach, a recursive exact solution to an approximation of the posterior distribution of the inverse problem is proposed. A Markov chain Monte Carlo algorithm can be used to efficiently simulate realizations from the correct posterior model. Two inversion studies based on real well log data are presented, and the main results are the posterior distributions of the reservoir properties of interest, the corresponding predictions and prediction intervals, and a set of conditional realizations. The first application is a seismic inversion study for the prediction of lithological facies, P- and S-impedance, where an improvement of 30% in the root-mean-square error of the predictions compared to the traditional Gaussian inversion is obtained. The second application is a rock physics inversion study for the prediction of lithological facies, porosity, and clay volume, where predictions slightly improve compared to the Gaussian inversion approach. 相似文献
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Like compositions in general, regionalized compositions present the problem of spurious spatial correlation. To avoid this problem, this paper uses the additive-logratio transformation of regionalized compositions, following techniques introduced over the last few years for the statistical analysis of compositional data. It leads to an appropriate definition of a spatial covariance structure to describe spatial dependence between regionalized variables subject to constant-sum constraints in the case of weak stationarity. To illustrate stated problems, simulated data are used. 相似文献
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达肯大坂岩群是欧龙布鲁克地块结晶基底的重要组成部分,在形成过程中保存了丰富的物质记录和演化信息,是研究欧龙布鲁克地块乃至我国西部古老地壳及构造演化的窗口。通过对达肯大坂岩群详细的物质组成及构造剖面研究,根据岩石组合及变质-变形特征,将其进一步细化为混合片麻岩岩段、(混合岩化)流变片麻岩岩段、条带状片麻岩岩段、片岩岩段和大理岩岩段,野外调查表明,达肯大坂岩群中发育多期构造变形作用,根据野外变形特征及各期变形的叠加改造关系,初步建立了达肯大坂岩群相对变形序列,为区域构造过程的探讨与对比提供了新的基础资料。 相似文献
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Work on the excavations at the ancient Etruscan settlement of Marzabotto (Bologna) restarted in 1988. These excavations, as they were worked, brought to light a complete urban layout represented primarily by foundations, courtyards, roads and wells. The site has been the focus of intensive experimentation to assess the feasibility of geophysical remote sensing in exploration archaeology. Different geophysical techniques have been tested at this site: geoelectric, electromagnetic, magnetic, and seismic methods. One of the methods tested was geophysical seismic tomography. This method utilizes straightray algorithms to map subsurface properties by analyzing the first signal arrival time. Seismic tomography treats the problem of identifying a buried structure as a wave propagation process by inverting the linearized wave equation to compute the spatial distribution of the slowness of the velocity. The purpose of our tomographic study is to further test the method and to guide archaeologists in their future excavations by locating and identifying buried structures. In particular, analyses are performed on the geometries, signal characteristics, discretization of the area, and constraints of the inversion algorithm in order to enhance the effectiveness of the tomographic reconstruction process and to reduce costs. A controlled experiment is presented for a typical Marzabotto buried structure with which it is possible to verify the effectiveness of the applied technique. It is demonstrated how proper field measures and an inversion test can provide reliable information that can be used to guide excavation work. © 1994 John Wiley & Sons, Inc. 相似文献
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A Frequency Matching Method: Solving Inverse Problems by Use of Geologically Realistic Prior Information 总被引：1，自引：1，他引：0
Katrine Lange Jan Frydendall Knud Skou Cordua Thomas Mejer Hansen Yulia Melnikova Klaus Mosegaard 《Mathematical Geosciences》2012,44(7):783-803
The frequency matching method defines a closed form expression for a complex prior that quantifies the higher order statistics of a proposed solution model to an inverse problem. While existing solution methods to inverse problems are capable of sampling the solution space while taking into account arbitrarily complex a priori information defined by sample algorithms, it is not possible to directly compute the maximum a posteriori model, as the prior probability of a solution model cannot be expressed. We demonstrate how the frequency matching method enables us to compute the maximum a posteriori solution model to an inverse problem by using a priori information based on multiple point statistics learned from training images. We demonstrate the applicability of the suggested method on a synthetic tomographic crosshole inverse problem. 相似文献
13.
Schistous rock can be considered—in a first approximation—as cross‐anisotropic linear elastic material. The determination of the corresponding material constants on the basis of the laboratory investigation of rock samples often fails, as the extraction of appropriate cores proves to be unfeasible (the cores disintegrate if the schistosity is pronounced). In this paper a new method is presented to determine the material constants of a linear elastic cross‐anisotropic rock on the basis of cavity expansion field tests, e.g. with a radial jack. To this purpose, an analytic approximation for the deformation of a hydrostatically loaded cylindrical cavity in cross‐anisotropic rock is derived which serves to the inverse analysis of the material parameters. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
14.
A football stadium with a capacity of a hundred thousand spectators is under construction over a karst terrain, 10 km west of the old town of Istanbul, Turkey. A large cavity of approximately 30 m3 was detected beneath the sports field through a number of boreholes so that a geophysical survey was required to further investigate a portion of the sports field. We utilized seismic refraction tomography and dc-electrical method with rotated Wenner array to delineate zones with solution voids and cavities. Total core recovery (TCR) was 5–15% from boreholes where zones with low velocities were identified through tomographic inversion, whereas TCR values were above 60% in zones with higher velocities. Both low velocity zones in the tomographic images and increasing resistivity anisotropy with depth appear to indicate that the cavity extends toward the west and south at a depth of approximately 8 m, although the southward and westward extension changes in character. 相似文献
15.
岩体力学是近年来应生产实践需耍而开始形成,井有所发展的学科。从它的应用中提出了若干重要的课题,首先是岩体力学属性问题,即从力学观点看来,岩体究竟是何种介质,具有什么特性:是弹性体或塑性体,是均一体或非均一体,是各向异性体或同性体,是连续体或不连续体等。它们决定岩体力学分析途径,因而是目前着重研究以求阐明的基本问题。限于水平,本文仅作粗浅探讨,谬误之处请读者批评指正。 相似文献
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Interpreting and modelling geometries of complex geologic structures from strike/dip measurements using manually-drafted structural form lines is labour intensive, irreproducible and inherently limited to two dimensions. Herein, the structural field interpolation (SFI) algorithm is presented that overcomes these limitations by constructing 3D structural form lines from the vector components of strike/dip measurements. The SFI interpolation algorithm employs an anisotropic inverse distance weighting scheme derived from eigen analysis of the poles to strike/dip measurements within a neighbourhood of user defined dimension and shape (ellipsoidal to spherical) and honours younging directions, when available. The eigen analysis also provides local estimates of the plunge vector and associated Woodcock distribution properties to assure plunge-normal structural form line reconstruction with unidirectional propagation of form lines across fold and fan structures. The method is advantageous for modelling geometries of geologic structures from a wide range of structurally anisotropic data. Modelled vector fields from three case studies are presented that reproduce the expected bedding-foliation geometry and provide reasonable representation of complex folds from local to regional scales. Results illustrate the potential for using vector fields to support geologic interpretation through the direct visualization of geometric trends of structural features in 3D. 相似文献
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地面地震初至波层析反演复杂表层速度结构方法 总被引：1，自引：0，他引：1
针对复杂表层结构的反演问题,作者研究了一套利用地面地震初至波层析反演表层速度结构的理论、方法和软件系统。该方法利用了地面地震直达波、迥折波、折射波以及三者组合的初至波,并采用具有空间变速优势的层析反演,可获得任意介质类型的表层速度结构。该方法的优点是野外施工简单(不需要在井中激发、接收),反演精度高,适应性强,反演所得到的表层速度结构可直接用于环境与工程项目的表层地质结构调查和评价。 相似文献