The best plane through data

Conclusions As can be seen from Table 1, the two trend surfaces give considerably different values. Our data were chosen not to fit any one plane and this is reflected in both of the trend surfaces. The program has been run with different data, and as the data tend toward a plane both trend surfaces become nearly identical as one would expect. We conclude that the type of plane to use for trend-surface analysis does indeed depend on the hypotheses of the fitting technique.     

Probabilistic constraints on structural lineament best fit plane precision obtained through numerical analysis

Understanding the orientation distribution of structural discontinuities using the limited information afforded by their trace in outcrop has considerable application, with such analysis often providing the basis for geological modelling. However, eigen analysis of 3D structural lineaments mapped at decimetre to regional scales indicates that discontinuity best fit plane estimates from such datasets tend to be unreliable. Here, the relationship between digitised lineament vertex geometry (coplanarity/collinearity) and the reliability of their estimated best fitting plane is investigated using Monte Carlo experiments. Lineaments are modelled as the intersection curve between two orthonormally oriented fractional Brownian surfaces representing the outcrop and discontinuity plane. Commensurate to increasing lineament vertex collinearity (K), systematic decay in estimated pole vector precision is observed from these experiments. Pole vector distributions are circumferentially constrained around the axis of rotation set by the end nodes of the synthetic lineaments, reducing the rotational degrees of freedom of the vertex set from three to one. Vectors on the unit circle formed perpendicular to this arbitrary axis of rotation conform to von Mises (circular normal) distributions tending towards uniform at extreme values of K. This latter observation suggests that whilst intrinsically unreliable, confidence limits can be placed upon orientation estimates from 3D structural lineaments digitised from remotely sensed data. A probabilistic framework is introduced which draws upon the statistical constraints obtained from our experiments to provide robust best fit plane estimates from digitised 3D structural lineaments.     

Heat extraction through a geothermal reservoir on an oblique fault plane

The heat extraction through a geothermal reservoir on an oblique fault plane in the earth's crust is considered. The fault could be modelled mechanically as a frictional contact interface of two elastic bodies. The heat is recovered by circulating fluid through the reservoir, and then the surface of the reservoir is cooled by the fluid. The analysis is based on the two-dimensional theory of quasi-static thermoelasticity. It is concluded from numerical calculations that a geothermal reservoir can be created on an oblique fault plane, and the opened region, i.e. the fluid-filled region, increases gradually with time during the heat extraction. Also discussed are the effects of the fluid pressure and the coefficient of friction on the behaviour of the reservoir.     

Navigating through SPASE to heliospheric and magnetospheric data

Virtual observatories have been introduced by the astrophysics community as an environment connecting distributed data sources with a unified interface. The heliophysics community soon recognized that they faced a similar problem of many distributed data sets with varying amount of information about them and several discipline specific virtual observatories have been established. Two of them, the virtual heliospheric observatory (VHO) and the virtual magnetospheric observatory (VMO), share a common architecture design with development efforts oriented towards a structured data search. This paper describes the VHO/VMO middleware and its components from metadata preparation and processing to the user interface.     

Structural study of Meghalaya plateau through aeromagnetic data

The study of aeromagnetic data over parts of Assam-Meghalaya has delineated major discontinuities representing faults/ fractures/ contacts/ shears and magnetic body axes, which helped in understanding the regional and structural setup of the area. The known Barapani and Dapsi Thrusts, Dudhnai Fault and three strong magnetic anomalies with reverse magnetisation have been delineated. The quantitative analysis of aeromagnetic data brought out the depths of magnetic interfaces and the magnetic picture of different layers, which also helped in understanding the regional and structural setup. The contact modeling across few profile sections showed the depths to the top of contacts and the map of magnetic-basement-depth-model revealed the undulations of the basement. Magnetic body axes of several magnetic anomalies and also several magnetic discontinuities representative of faults/ fractures/ contacts/ shears system in the area along with five potential blocks for mineral prospecting are the main outcome of this exercise. The seismotectonic activity associated with the magnetic features has also been studied to understand the structural setup.     

A grid-search inversion method looking for the best classification of polyphase fault/slip data

A novel, grid search-based stress inversion method is developed in this paper to find the global minima in the solution region for the classification of fault/slip data into many single-phase subsets. Exhaustively repetitious grid searches are taken to deal with possible local minima, in a departure from existing grid search-based inversion methods. Two stopping rules, to stop at the abrupt change of the objective function or at the least change of the classification, are adopted in the method to look for the best classification. Much calculation time is saved by using a modified version of conventional grid search. The feasibility of this proposed method is demonstrated by applying it to two artificial examples and two real examples. However, enormous time in calculation is still needed in the case of a data set either with a large number of data or for a large number of assigned subsets.     

The superposition of compaction and plane strain

The coaxial and non-coaxial superposition of tectonic (biaxial or plane) strain on compactional (uniaxial) strain is examined and total finite strains and deformation paths calculated. Both prolate and oblate strains may result, depending on the relative orientations of the two strains. The implications of superposed strain are discussed in relation to naturally occurring strains in rocks, and various patterns of finite strain and deformation fields recognized.     

The problem of shearing along axial plane foliations

The structural significance of axial plane foliations cannot be understood unless we make a distinction between rotation of the material plane foliation and rotation of the geometrically defined XY-plane of the strain ellipsoid. If the foliation rotates as a material plane at any stage of deformation, then its final orientation will be different from that of the XY-plane. It is suggested that reorientation of foliation takes place by some combination of the formation of foliation (e.g. recrystallization) along the XY-plane and passive rotation of the material plane foliation in the same continuous deformation. The deviation between the foliation and the XY-plane is then much less than 5 degrees. However, because of this deviation, a considerable amount of shear strain may develop along the foliation. The analysis, thus, explains how a foliation can be approximately parallel to the XY-plane and yet be a plane of shearing.     

锚索框架梁加固平面滑动型边坡地震动力响应

设计并完成了一个缩尺比例为1:20的锚索框架梁加固平面滑动型边坡的振动台试验,通过改变输入地震波类型和峰值,研究了边坡体及支护结构的动力响应特性。试验结果表明：锚固边坡体的整体稳定性较好,地震造成的破坏主要为滑体顶部震碎和无约束坡面岩土体剥蚀、掉块;地震波在经过软弱夹层时存在能量聚集效应,不同地震波下滑体重心处加速度放大系数的差异性随输入地震波峰值的增加而减小;锚索在地震时表现出协同工作的特性,预应力损失最先发生在坡顶,然后向坡体中下部转移;在锚索框架梁的抗震设计时,应考虑边坡体上部的加速度放大效应和锚索预应力损失对边坡整体稳定性的影响。试验结果为合理考虑预应力锚索框架梁的抗震设计提供有益的参考。     

Identification of sedimentary cycles through Fourier analysis of geochemical data

Trace elements are sensitive to slight shifts in the chemical equilibrium of a body of water, and as a result they can be expected to reflect cyclical events in the earth's history. Geochemical data from a section of Upper Jurassic (Kimmeridgian) bituminous sediments in Great Britain, 20 m thick, have been examined by single Fourier series analysis, thereby permitting an objective assessment of sedimentary cycles. Subjectivity only enters into the final interpretative stage.Assumptions made as to the rate of deposition of these sediments have indicated several superimposed periodicities with respective durations of (?) 200,000, 100,000, 40,000, 14,000, and 11,000 years.Comparison is made with long-term cyclic durations estimated by other workers. Several of these periods are coincident with the duration of astronomical phenomena which could cause climatic fluctuations.     

Prediction of minesite-drainage chemistry through closure using operational monitoring data

Post-mining drainage chemistry depends strongly on geochemical and hydrologic processes that occur during the operational years. Where routine operational monitoring data are abundant, the dominant processes can often be evaluated with no additional, special studies. Thus, post-mining drainage chemistry can be predicted with confidence based on the operational data. This is referred to here as ‘empirical drainage-chemistry modelling’ (EDCM).This paper presents examples of EDCM using routine monitoring databases from several minesites, each containing thousands of analyses and spanning up to 30 years of mine operation and closure. Simple statistical interpretations in the EDCM can reveal annual cycles and trends that aqueous concentrations display during operation and into closure.A new compilation of 12 EDCM equations for copper versus pH is presented to illustrate similar trends with pH among the sites. However, this compilation also shows that average-annual copper concentrations at a particular pH can vary by three orders of magnitude, reflecting site-specific factors. Also, a new case study comparing actual closure concentrations to those predicted with EDCM in 1991 demonstrates that predictive accuracy is within a factor of two.     

Iceland's best kept secret

The ‘forgotten fjords’ and ‘deserted inlets’ of NE‐Iceland, in the region between Borgarfjörður Eystri and Loðmundarfjörður, are not only prominent because of their pristine landscape, their alleged elfin settlements, and the puffins that breed in the harbour, but also for their magnificent geology. From a geological point of view, the area may hold Iceland's best kept geological secret. The greater Borgarfjörður Eystri area hosts mountain chains that consist of voluminous and colourful silicic rocks that are concentrated within a surprisingly small area (Fig. 1 ), and that represent the second‐most voluminous occurrence of silicic rocks in the whole of Iceland. In particular, the presence of unusually large volumes of ignimbrite sheets documents extremely violent eruptions during the Neogene, which is atypical for this geotectonic setting. As a group of geoscientists from Uppsala University (Sweden) and the Nordic Volcanological Center (NordVulk, Iceland) we set out to explore this remote place, with the aim of collecting material that may allow us to unravel the petrogenesis of these large volumes of silicic rocks. This effort could provide an answer to a long‐standing petrological dilemma; the question of how silicic continental crust is initially created. Here we document on our geological journey, our field strategy, and describe our field work in the remote valleys of NE‐Iceland.     

Solution for a plane strain rough‐walled hydraulic fracture driven by turbulent fluid through impermeable rock

The impact of turbulent flow on plane strain fluid‐driven crack propagation is an important but still poorly understood consideration in hydraulic fracture modeling. The changes that hydraulic fracturing has experienced over the past decade, especially in the area of fracturing fluids, have played a major role in the transition of the typical fluid regime from laminar to turbulent flow. Motivated by the increasing preponderance of high‐rate, water‐driven hydraulic fractures with high Reynolds number, we present a semianalytical solution for the propagation of a plane strain hydraulic fracture driven by a turbulent fluid in an impermeable formation. The formulation uses a power law relationship between the Darcy‐Weisbach friction factor and the scale of the fracture roughness, where one specific manifestation of this generalized friction factor is the classical Gauckler‐Manning‐Strickler approximation for turbulent flow in a rough‐walled channel. Conservation of mass, elasticity, and crack propagation are also solved simultaneously. We obtain a semianalytical solution using an orthogonal polynomial series. An approximate closed‐form solution is enabled by a choice of orthogonal polynomials embedding the near‐tip asymptotic behavior and thus giving very rapid convergence; a precise solution is obtained with 2 terms of the series. By comparison with numerical simulations, we show that the transition region between the laminar and turbulent regimes can be relatively small so that full solutions can often be well approximated by either a fully laminar or fully turbulent solution.