A new cluster algorithm for orientation data

An algorithm to classify data points on the sphere in distinct cluster groups is defined. The characteristics of the cluster groups and the rule for assigning data to the groups are related to a continuous differentiable density estimation. The modes of the estimated density are assumed to be representative of the groups; data points are then assigned to the mode reached by the steepest ascent. The major advantage of this procedure is its sensitivity in detecting cluster groups independently of their geometry and configuration. As a consequence, the procedure is capable of handling orientation data that may be arranged in girdles.     

On the least-squares fit of small and great circles to spherically projected orientation data

Given the direction cosines a _i ^′ = (a ₁ ⁱ , a ₂ ⁱ , a ₃ ⁱ )corresponding to a set of pspherically projected fabric poles, an initial estimate x′ = (x₁, x₂, x₃, x₄)for the angular radius x₄,and direction cosines of the center of the least-squares small circle which minimizes the sum of the squares of the angular residuals $$r = \sum\limits_p {\left[ {x_4 - \cos ^{ - 1} \left( {a_1^i x_1 + a_2^i x_2 + a_3^i x_3 } \right)} \right]} ^2 $$ can be iteratively improved by taking x_j+1 = x_j + Δxwhere x_j is the value of xat the jth iteration and $$\Delta x = - H_j^{ - 1} \left[ {q_j + x_j \left( {x'_j H_j^{ - 1} x_j } \right)\left( {q_j - x'_j H_j^{ - 1} q_j } \right)} \right],$$ where As an initial approximation for xwe have found it convenient to ignore the fact that the data are constrained to lie on the surface of the reference sphere and to use the parameters of a least-squares plane through the given poles. Generalization of this approach to fitting variously constrained great and small circles is easily made. The relative merits of differently constrained fits to the same data can be tested approximately if it is assumed that the errors in the location of the poles are isotropic and normally distributed. It is thus possible to statistically assess the relative significance of conflicting structural models which predict different geometrical patterns of fabric elements.     

Comparison of structural and least-squares lines for estimating geologic relations

Two different goals in fitting straight lines to data are to estimate a true linear relation (physical law) and to predict values of the dependent variable with the smallest possible error. Regarding the first goal, a Monte Carlo study indicated that the structural-analysis (SA) method of fitting straight lines to data is superior to the ordinary least-squares (OLS) method for estimating true straight-line relations. Number of data points, slope and intercept of the true relation, and variances of the errors associated with the independent (X) and dependent (Y) variables influence the degree of agreement. For example, differences between the two line-fitting methods decrease as error in X becomes small relative to error in Y. Regarding the second goal—predicting the dependent variable—OLS is better than SA. Again, the difference diminishes as X takes on less error relative to Y. With respect to estimation of slope and intercept and prediction of Y, agreement between Monte Carlo results and large-sample theory was very good for sample sizes of 100, and fair to good for sample sizes of 20. The procedures and error measures are illustrated with two geologic examples.     

Determination and interpretation of preferred orientation with texture goniometry: An application of indicators to maximum entropy pole- to orientation-density inversion

The probability density function of orientations of crystals generally cannot be measured directly without destruction of the specimen. Therefore it is usual practice to sample pole density functions of several crystal forms in diffraction experiments with a texture goniometer. Determining a reasonable orientation density function from experimental pole density functions is then the crucial prerequisite of quantitative texture analysis. This mathematical problem may be addressed as a tomographic inversion problem specified by the crystal and statistical specimen symmetries and the properties of the diffraction experiment. Its solution with maximum entropy preferred orientation portion and maximum uniform portion is proposed because it yields the most conservative orientation density function with systematically reduced correlation effects, thus avoiding artificial texture ghost≓ components caused by the specific properties of the diffraction experiment.     

基于GIS空间分析的虚拟钻孔确定与实现方法

在三维地质建模过程中,通过引入一定数量的虚拟钻孔,对地层分界面几何形态更加精确的控制,不仅能够明显改善地质分界面网格的质量,而且能够提高模型精度和可视化效果。现有虚拟钻孔的引入途径主要通过手工添加实现,受人为主观因素影响较大,且自动化水平低,耗时、费力,针对这一问题,提出了一种基于GIS空间分析的虚拟钻孔确定与实现方法。以地质勘查获取的钻孔数据和地质剖面图为数据源,在ArcGIS平台的支持下,综合运用自动矢量化（Arc Scan）、要素转点（Feature To Point）、创建TIN （Create Tin）、TIN转三角形（Tinto Triangle）、泰森多边形（Create Thiessen Polygons）和相交（Intersect）等空间分析和文件转换工具,分别生成断层构造和建模区域内的二维（2D）虚拟钻孔点;而后,在利用插值工具生成各地层栅格表面的基础上,结合图形插值（Interpolate Shape）工具将2D虚拟钻孔点投影为三维（3D）虚拟钻孔;然后,利用Model Builder可视化建模工具设计了生成虚拟钻孔的模型,实现虚拟钻孔创建的自动化;最后,将获得的3D虚拟钻孔应用于三维地质建模,并进行了建模对比实验,结果表明,该方法具有一定有效性、实用性和可操作性。     

Compositional data analysis of Holocene sediments from the West Bengal Sundarbans,India: Geochemical proxies for grain-size variability in a delta environment

This paper is part of a special issue of Applied Geochemistry focusing on reliable applications of compositional multivariate statistical methods. This study outlines the application of compositional data analysis (CoDa) to calibration of geochemical data and multivariate statistical modelling of geochemistry and grain-size data from a set of Holocene sedimentary cores from the Ganges-Brahmaputra (G-B) delta. Over the last two decades, understanding near-continuous records of sedimentary sequences has required the use of core-scanning X-ray fluorescence (XRF) spectrometry, for both terrestrial and marine sedimentary sequences. Initial XRF data are generally unusable in ‘raw-format’, requiring data processing in order to remove instrument bias, as well as informed sequence interpretation. The applicability of these conventional calibration equations to core-scanning XRF data are further limited by the constraints posed by unknown measurement geometry and specimen homogeneity, as well as matrix effects. Log-ratio based calibration schemes have been developed and applied to clastic sedimentary sequences focusing mainly on energy dispersive-XRF (ED-XRF) core-scanning. This study has applied high resolution core-scanning XRF to Holocene sedimentary sequences from the tidal-dominated Indian Sundarbans, (Ganges-Brahmaputra delta plain). The Log-Ratio Calibration Equation (LRCE) was applied to a sub-set of core-scan and conventional ED-XRF data to quantify elemental composition. This provides a robust calibration scheme using reduced major axis regression of log-ratio transformed geochemical data. Through partial least squares (PLS) modelling of geochemical and grain-size data, it is possible to derive robust proxy information for the Sundarbans depositional environment. The application of these techniques to Holocene sedimentary data offers an improved methodological framework for unravelling Holocene sedimentation patterns.     

多孔含水岩层的相似材料配比研究

以石膏、浮石、硅藻土等材料为相似材料对多孔含水岩层进行相似材料模拟。试验中采用四因素（硅藻土水泥石膏比、标准砂浮石比、骨胶比、重晶石骨料比）、五水平的正交试验方法,分别对多孔含水岩层的相似材料试件进行密度、单轴抗压强度、孔隙率、弹性模量以及软化系数的测定,得出相应的物理力学性质指标,采用直观分析法分析各因素对物理力学性质的影响规律。分析结果表明：由于各配比度不同,相似材料强度分布范围较广,在与多孔岩层的岩石参数对比中发现,在一定的相似条件下,基本符合多孔岩层岩石的相似要求;硅藻土含量与密度、抗压强度、弹性模量、孔隙率呈负相关,与软化系数呈正相关;浮石含量与密度、抗压强度、弹性模量、软化系数呈负相关,与孔隙率呈正相关。所加入的两种材料可较好地模拟样品的多孔特性。在允许波动范围之内,所建立的模拟多孔含水岩层的经验方程可用于工程实践。     

水泥和石膏胶结相似材料配比的确定方法

对以水泥和石膏为胶结材料、石英砂和重晶石粉为骨料的相似材料,规范了其制作原料与工艺,以砂胶比（骨料与胶结材料质量比）、水膏比（水泥与石膏质量之比）和重晶石含量（重晶石质量占骨料百分比）为控制因素,设计了一个正交试验,开展了称重、单轴压缩试验,获得了不同配比相似材料的密度、单轴抗压强度和弹性模量等物理力学性质指标。采用极差分析法分析了各因素的敏感性,研究了各因素对相似材料参数的影响规律。研究表明：重晶石含量对相似材料密度有明显的控制作用,而砂胶比和水膏比对密度也有明显的影响;砂胶比对相似材料单轴抗压强度和弹性模量影响最大,水膏比和重晶石含量的影响次之。相似材料密度随砂胶比的增大而降低,随水膏比和重晶石含量的增大而增大;抗压强度随砂胶比的增大而显著降低,但随着水膏比和重晶石含量的增大而缓慢增大;弹性模量随砂胶比的增大而显著降低,随重晶石含量增大而增大,随水膏比增大而缓慢升高。采用MATLAB程序对试验数据进行多元线性回归分析,得到确定相似材料配比的经验方程。工程应用证明,采用经验方程计算得到相似材料配比,并按规范的制作工艺,可以得到满足试验要求的相似材料。     

TR method (TRM): A separation and stress inversion method for heterogeneous fault-slip data driven by Andersonian extensional and compressional stress regimes

The recently proposed TR method (TRM) which uses the slip preference of the faults to separate heterogeneous fault-slip data in extensional and compressional Andersonian stress regimes, is enhanced so as to determine stress tensors with the use of the Wallace–Bott slip criterion. Published natural fault-slip data from the extensional region of Tympaki, Crete, Greece and artificial fault-slip data modeled from the Chelungpu thrust, activated during the 1999 Chi–Chi earthquake in Taiwan, have been used as case studies. In the first case, the fault-slip data previously considered as homogeneous might actually be of heterogeneous origin as they determine two distinct stress tensors that both fit well with the neotectonic faulting deformation of the region. In the second case, where the fault-slip data belonging to three different subsets are of low diversity, the TRM succeeds in defining the driving stress tensors. The Misfit Angle minimization criterion can adequately separate the fault-slip data between two subsets when the percentage of the “Stress Tensor Discriminator Faults” is higher than approximately 70%.     

地震资料采集监控及评价系统的开发

介绍了开发地震资料采集监控及评价系统的必要性,详细地论述了系统包含的各部分功能以及在实际生产中针对不同地区不同资料的使用方法。使用该系统进行计算机自动化监理评价,可以极大地提高监理评价工作的效率。该系统的成功开发,为规范和提高地震资料监理质量提供了技术保障。     

基于主成分分析的化探异常圈定新方法——以新疆西准噶尔地区1:50000岩屑数据为例

以新疆西准噶尔地区阿克巴斯陶1∶50 000万岩屑数据为对象,利用相关、偏相关分析和R型聚类分析确定研究区成矿元素组合为Cu-Mo-Zn-W-Sb-Bi-As(铜钼成矿组合)与Au-As-Bi(金成矿组合);基于主成分分析,以线性方法将2组成矿元素重组为新的变量N1(Cu-Mo-Zn-W-Sb-Bi-As)与N2(Au-Bi-As),新变量中各元素权重根据主成分分析所得特征向量值大小决定;运用分形含量-面积法提取新变量异常下限并生成综合异常图。结合野外地质检查,成功圈定两处成矿潜力区,为下一步工作提供有力依据。     

A method for seafloor classification using directional variograms, demonstrated for data from the western flank of the Mid-Atlantic Ridge

Seafloor classification is aimed at quantitatively characterizing seafloor properties such as roughness and anisotropy, and at using such spatial characteristics to distinguish geological provinces automatically. From geostatistical principals, a variogram method is developed for seafloor classification and it is demonstrated for data from the western flank of the Mid-Atlantic Ridge at 25°45N to 26°40N. This study uses HYDROSWEEP bathymetric data which have been ping-edited to flag erroneous data records, and navigation corrected. The classification method can handle the resultant data gaps inside the survey swaths as well as interpret data from several swaths. For a suite of test areas representative of different geological provinces, directional variograms are calculated, and characteristic parameters are extracted for the classification. Examples include a sediment pond, abyssal hill terrain in several segments and of variable spacing, inside and outside corners of ridge discontinuities, and mixed morphological forms. The dependency of the results on random or regular subsampling and on the size of the test area is investigated.     

井中三分量磁测确定矿体方位和空间位置的方法

井中三分量磁测能较好地判断异常体的性质,进而判断磁性体的方位和空间位置,通常联合地面磁测可以更准确地判断地下矿体赋存情况,确定矿体产状、延伸方向及延深,指导布钻,提高见矿率.笔者主要分析了球体、薄板状体的磁场分布特征,总结磁场分布特征与磁性体的方位、磁化方向、倾斜方向等之间的相互对应关系,研究判断矿体方位、确定矿体空间位置的方法.井中三分量磁测是配合钻探寻找地下深部磁性矿体、了解其赋存情况的有效手段.将该方法应用于海南石碌铁矿某工区ZK1102井,提高了确定地下矿体空间位置的精确度,为继续钻进、终止布孔工作以及磁性矿体的储量评估提供参考.     

煤田资料的铀矿二次开发技术及其找矿意义——以二连盆地ZS煤田铀矿点的发现为例

在中国北方主要盆地铀矿地质调查工作中,煤田自然伽马异常作为主要矿化信息和找矿线索,为一系列铀矿床(点)的快速发现奠定了坚实基础。为进一步提高煤田资料铀矿二次开发的高效性和准确性,运用水成铀矿理论,以中国二连盆地ZS煤矿区典型铀矿点的发现为例,初步探讨了煤田资料的铀矿二次开发技术,提出了"异常筛选与选区分析、原位验证与环境判别、等时地层格架建立与沉积体系分析、综合分析与靶区定位"四位一体的煤矿区铀矿地质调查模式。这对中国北方含煤盆地铀矿地质调查工作提供了新的找矿思路和技术路线,具有较重要的指导意义。     

Salt movements in the Northeast German Basin and its relation to major post-Permian tectonic phases—results from 3D structural modelling, backstripping and reflection seismic data

The NW–SE-striking Northeast German Basin (NEGB) forms part of the Southern Permian Basin and contains up to 8 km of Permian to Cenozoic deposits. During its polyphase evolution, mobilization of the Zechstein salt layer resulted in a complex structural configuration with thin-skinned deformation in the basin and thick-skinned deformation at the basin margins. We investigated the role of salt as a decoupling horizon between its substratum and its cover during the Mesozoic deformation by integration of 3D structural modelling, backstripping and seismic interpretation. Our results suggest that periods of Mesozoic salt movement correlate temporally with changes of the regional stress field structures. Post-depositional salt mobilisation was weakest in the area of highest initial salt thickness and thickest overburden. This also indicates that regional tectonics is responsible for the initiation of salt movements rather than stratigraphic density inversion.Salt movement mainly took place in post-Muschelkalk times. The onset of salt diapirism with the formation of N–S-oriented rim synclines in Late Triassic was synchronous with the development of the NNE–SSW-striking Rheinsberg Trough due to regional E–W extension. In the Middle and Late Jurassic, uplift affected the northern part of the basin and may have induced south-directed gravity gliding in the salt layer. In the southern part, deposition continued in the Early Cretaceous. However, rotation of salt rim synclines axes to NW–SE as well as accelerated rim syncline subsidence near the NW–SE-striking Gardelegen Fault at the southern basin margin indicates a change from E–W extension to a tectonic regime favoring the activation of NW–SE-oriented structural elements. During the Late Cretaceous–Earliest Cenozoic, diapirism was associated with regional N–S compression and progressed further north and west. The Mesozoic interval was folded with the formation of WNW-trending salt-cored anticlines parallel to inversion structures and to differentially uplifted blocks. Late Cretaceous–Early Cenozoic compression caused partial inversion of older rim synclines and reverse reactivation of some Late Triassic to Jurassic normal faults in the salt cover. Subsequent uplift and erosion affected the pre-Cenozoic layers in the entire basin. In the Cenozoic, a last phase of salt tectonic deformation was associated with regional subsidence of the basin. Diapirism of the maturest pre-Cenozoic salt structures continued with some Cenozoic rim synclines overstepping older structures. The difference between the structural wavelength of the tighter folded Mesozoic interval and the wider Cenozoic structures indicates different tectonic regimes in Late Cretaceous and Cenozoic.We suggest that horizontal strain propagation in the brittle salt cover was accommodated by viscous flow in the decoupling salt layer and thus salt motion passively balanced Late Triassic extension as well as parts of Late Cretaceous–Early Tertiary compression.     

SLIP4EX – A Program for Routine Slope Stability Analysis to Include the Effects of Vegetation, Reinforcement and Hydrological Changes

SLIP4EX is a straightforward computer program developed in connection with the EU funded ECOSLOPES project for routine stability analysis and the assessment of the contribution of vegetation to slope stability. The slope section is drawn up and dimensions and parameters are fed in to the Microsoft Excel based program for stability calculations and comparisons of Factors of Safety using different methods of analysis (Bishop, Janbu, Fellenius, Simple, Greenwood). The background and assumptions involved in the derivation of each of the methods is briefly described. The simplicity of the program enables the user to understand the nature of the analysis, explore the parameter assumptions made and compare the different methods of analysis. Soil reinforcement by geosynthetic layers or anchors, and vegetation effects of enhanced cohesion, changed water pressures, mass of vegetation, wind forces and root reinforcement forces are readily included in the analysis. The program is freely available on request from the Author.     

潮汐沉积韵律计算新方法及其应用 ——以四川江油地区中三叠统雷口坡组藻白云岩为例

提出一种新的高精确度的方法来计算沉积旋回韵律,即以样品断面光学灰度参数作为韵律沉积变化的替代指标,利用数字图像分析软件,通过最小二乘法、一阶差分法等数据处理后,定量计算沉积旋回韵律。对采自四川江油西南部中三叠统雷口坡组的纹层藻白云岩样品进行研究,观察样品抛光面和薄片,确定藻白云石具有明显的潮汐沉积韵律纹层。应用此方法计算得出研究区样品共有217个潮汐层偶对,层偶对最大厚度为4.2mm,通过人工计数对比证明了该方法的可行性。这种技术方法与传统方法相比更省时、更高效,可推广性高,同时也可应用于其它类型频段韵律旋回中。     

Evaluating hazard results for Switzerland and how not to do it: A discussion of “Problems in the application of the SSHAC probability method for assessing earthquake hazards at Swiss nuclear power plants” by J-U Klügel

The PEGASOS project was a major international seismic hazard study, one of the largest ever conducted anywhere in the world, to assess seismic hazard at four nuclear power plant sites in Switzerland. Before the report of this project has become publicly available, a paper attacking both methodology and results has appeared. Since the general scientific readership may have difficulty in assessing this attack in the absence of the report being attacked, we supply a response in the present paper. The bulk of the attack, besides some misconceived arguments about the role of uncertainties in seismic hazard analysis, is carried by some exercises that purport to be validation exercises. In practice, they are no such thing; they are merely independent sets of hazard calculations based on varying assumptions and procedures, often rather questionable, which come up with various different answers which have no particular significance.