Quantification of Natural Fracture Surfaces Using Fractal Geometry

The purpose of this paper is to present an extensive evaluation of the methods to calculate the fractal dimension of natural fracture surfaces. Three methods; variogram analysis (VA), power spectral density (PSD), and roughness-length method (RMS) are applied to 2-D surface data (PSD) and 1-D profiles (VA and RMS) extracted from the surface data of 54 mm diameter crystallized limestone samples. Surface topography of the samples is quantified through a newly designed fully automated device. Before the application, self-affinity of the surface roughness and the applicability of these methods are validated using synthetically generated fractal surfaces. Fractal dimension values of the profiles are obtained as between 1 and 1.5 with a few exceptions. VA and RMS methods yield consistent fractal dimensions while the PSD values are lower than those of the other two methods. In terms of practical applicability, the VA is found more convenient than other two methods because there still exists shortcomings with the PSD and RMS methods due to difficulties in the mathematical analysis of the plots whose slopes are used in the computation of fractal dimension. However, it is observed that the data of limited size fracture surfaces are convenient for fractal analysis and the results are promising for further applications if the fracture surface size is restricted like cores recovered from deep boreholes.     

A New Categorization of Types of Slope Collapse in Mountain Areas

Regarding the collapse of a special type of soil erosion in mountain areas. Studying its types, processes and stages can provide a scientific basis for prediction. Collapses can be classified into three types, natural, man-made and compound, and each type can be subdivided into four kinds, break-falling, pull-splitting, toppling and slipping. The processes of collapse are creep-deformation, deformation-development and break-out. The second one is subdivided into two periods, the gentle and intense.     

冻土断裂力学在桩基冻拔稳定计算中的应用

对桩基冻拔的冻土工程问题进行了断裂力学分析,并给出简化模。在此基础上讨论了断裂判据以及应力强度因子的计算表达式。     

地下水的分类和基岩裂隙水的基本概念

论文深入地论述了“地下水类型”及“基岩裂隙水”这两个重要概念的认识过程。根据新近的地下水勘探资料,论文指出了目前通用的地下水介质分类存在的问题,提出了地下水介质分类的新方案和基岩裂隙水的新概念。     

沉积盆地构造应力场研究综述

阐述了构造应力场在盆地演化分析、油气的生成和运聚、裂缝形成等方面的应用现状及发展趋向,指出在盆地演化分析中构造应力场的研究应以盆地形成演化过程中的原始沉积特征为依据,构造应力与流体（油、气、水）之间的相互作用表现为应力场、温度场、渗流场的相互耦合,定量研究它们的耦合关系及时空变化规律是认识构造应力和流体作用的主要途径。比较客观地探讨了构造应力场模拟、构造应力大小和方向、起源等问题。     

Scattering attenuation and the fractal geometry of fracture systems

Scattering of seismic waves can be shown to have a frequency dependenceQ ^{–1 3–v} if scattering is produced by arrays of inhomogeneities with a 3D power spectrumW _3D(k) k ^–v. In the earth's crust and upper mantle the total attenuation is often dominated by scattering rather than intrinsic absorption, and is found to be frequency dependent according toQ ^–1 , where –1<–0.5. IfD ₁ is the fractal dimension of the surface of the 3D inhomogeneities measured on a 2D section, then this corresponds respectively to 1.5<D ₁1.75, since it can be shown that =2(D ₁–2). Laboratory results show that such a distribution of inhomogeneities, if due to microcracking, can be produced only at low stress intensities and slow crack velocities controlled by stress corrosion reactions. Thus it is likely that the earth's brittle crust is pervaded by tensile microcracks, at least partially filled by a chemically active fluid, and preferentially aligned parallel to the maximum principal compressive stress. The possibility of stress corrosion implies that microcracks may grow under conditions which are very sensitive to pre-existing heterogeneities in material constants, and hence it may be difficult in practice to separate the relative contribution of crack-induced heterogeneity from more permanent geological heterogeneities.By constrast, shear faults formed by dynamic rupture at critical stress intensities produceD ₁=1, consistent with a dynamic rupture criterion for a power law distribution of fault lengths with negative exponentD. The results presented here suggest empirically thatD ₁-1/2(D+1), thereby providing the basis for a possible framework to unify the interpretation of temporal variations in seismicb-value (b-D/2) and the frequency dependence of scattering attenuation ().This is PRIS contribution 046.     

陕西韩城龙湾—上峪口现今破裂带成因探讨

陕西韩城西山古生代地层中存在一系列现代破裂形变现象。本文对该现象作了较详细的描述,认为它处在一个特殊的构造部位与地貌部位,在人类活动(采煤)的环境条件下,因重力作用而造成。同时认为该现象作为一次古代大地震遗迹的看法,证据尚不充分     

钻孔雷达探测地下裂缝

钻孔雷达是地质雷达的一种特殊模式,与通常的地质雷达比起来,有几个显著的特点。比如,利用钻孔接近地下的某个区域,天线可以相对接近所要测量的地质异常体或目标,从而导致在较深的范围对目标的精确测量。实验场地位于北京西部的一个石灰岩的小山上。该处有一组钻孔,并被大量的裂缝所切割。在这些钻孔中,进行了单孔反射测量和跨孔测量。测量的数据经过处理和解释表明,在该场地雷达的径向探测范围可达30 m,地下裂缝的分布可以形成清晰的图像。可以看到很多裂缝,它们距钻孔的距离及倾角都可以确定下来。在有些情况下,确定裂缝分布的方位是可能的。     

Spatial Distribution,Scaling and Self-similar Behavior of Fracture Arrays in the Los Planes Fault,Baja California Sur,Mexico

We present a case of detailed analysis of fracture arrays spanning four orders of magnitude in length; all of them measured at a single natural site by acquiring images at progressively larger scales. There is a high dispersion of cumulative-length exponents, box dimensions and fracture densities. However, the fractal analysis supports the fractal nature of fracture arrays. Our data indicate the existence of an upper limit for the density parameters, as similarly reported by other authors. We prove that box dimension is in inverse relation with fracture concentration and in direct relation with fracture density. These relations are also observed in our data and additionally there is an upper limit for the box dimensions. We interpret the dispersion in our results as more fundamental than methodological problems. It represents a truncation in the complete evolution of the fracture systems because in natural cases strain initiates overprinting of previous fracture arrays. Considering that larger fractures accommodate strain more efficiently than small fractures, the generation of small fractures is inhibited in the presence of pre-existing larger fractures. Maximum values of fracture density prevent accommodating an excess of strain in a single or restricted range of scales; we claim this condition produces migration of fracturing to larger scales originating fracture scaling.     

Testing the Porcupine Plate hypothesis

The Porcupine Plate, postulated in 1986 to explain difficulties in reconstructing anomalies 21 and 24 in the North Atlantic, is re-examined. Focusing sharply on the spreading segments nearest to Charlie-Gibbs Fracture Zone casts doubt on the Porcupine Plate hypothesis.