Effect of sampling and linkage on fault length and length–displacement relationship

The power-law exponent (n) in the equation: D=cL ⁿ , with D = maximum displacement and L = fault length, would be affected by deviations of fault trace length. (1) Assuming n=1, numerical simulations on the effect of sampling and linkage on fault length and length–displacement relationship are done in this paper. The results show that: (a) uniform relative deviations, which means all faults within a dataset have the same relative deviation, do not affect the value of n; (b) deviations of the fault length due to unresolved fault tip decrease the values of n and the deviations of n increase with the increasing length deviations; (c) fault linkage and observed dimensions either increase or decrease the value of n depending on the distribution of deviations within a dataset; (d) mixed deviations of the fault lengths are either negative or positive and cause the values of n to either decrease or increase; (e) a dataset combined from two or more datasets with different values of c and orders of magnitude also cause the values of n to deviate. (2) Data including 19 datasets and spanning more than eight orders of fault length magnitudes (10⁻²–10⁵ m) collected from the published literature indicate that the values of n range from 0.55 to 1.5, the average value being 1.0813, and the peak value of n _d (double regression) is 1.0–1.1. Based on above results from the simulations and published data, we propose that the relationship between the maximum displacement and fault length in a single tectonic environment with uniform mechanical properties is linear, and the value of n deviated from 1 is mainly caused by the sampling and linkage effects.     

西藏俄卡地银多金属异常区地球化学

异常形态、分布严格受推覆断裂控制,范围大、浓集中心明显,浓度变化及因子载荷表明。区内找Ag、Pb有利,而Sb又为其最佳指示元素。     

电阻率图像中的地下水和断层

目的：将电阻率层析成像应用于探测潜伏断层的研究中，本文发现了断层和地下水的一些基本电阻率分布特征，这对于工程物探意义重大，一般情况下，断层两侧具有不同的电阻率特征，但是，根据电阻率层析图像中的电阻率分布，通常难以区分断层和地下水层，这是因为两者不仅都具有低电阻率值，而且还具有非常相似的电阻率异常特征。资料和方法：运用电阻率层析图像的数据，电阻率层析图像中的断层会呈现如下特征：1）由于孔隙度的加大和地下水的存在，使得断层表现出高角度的低阻线性结构。它们既可以出现在浅部盖层中，也可以存在于深部基岩中，特别是在深部区域，它们尤为明显；2）它们还呈现出高角度的线性梯度带，在该梯度带两边的电阻率结构出现整体性的差异，通常情况下，正断层的上盘表现出低阻或／和班驳状的高阻和低阻扰动区，而下盘则为完整的高阻区，这与逆冲断层正好相反；3）与断层有关的电阻率异常区常常具有良好的大尺度水平连续性，并且可以追瞎异常区附近的精细电性结构。而地下水的电阻率特征为：1）如果没有裂隙，地表水所引起的低阻区非常浅，即使存在丰富的水源以及高孔隙度的砾岩和中粗砂。一般情况下，其底端深度不超过强风化区；2）地下水的电阻率值非常低，特别在高矿化度的地区。地下水，包括岩溶水和砂岩水，的电阻率总显示出局部水平延伸或／和面团状特征；3）地下水层的深度朝某个固定方向逐渐增加，并且其电阻率图像会随季节而变；4）一般情况下，在水下渗的地区，会出现降水漏斗，其上部为高阻，而下部为低阻，从而便形成了“Y”或“V”字型的典型结构。结果：利用上述的基本特征一般可以区分断层和地下水。结论：仅依靠电阻率层析图像，可能极难准确地区分断层和裂隙水，这是因为裂隙水不但可能具有高角度的低阻线性结构，而且在一定尺度上具有很好的水平连续性，还有，由于电阻率层析成像较差的垂直分辨率，难以精确确定断层的上端点位置，所以结合其它的物探手段如钻探和浅层地震勘探是非常必要的。     

岩石断裂作用的复杂性和混沌动力学

断裂是一个复杂的动力学体系,受到岩石结构、反应、流体迁移、应力、岩石变形和力学等多种地质因素和过程的耦合控制。本文建立了断裂体系的反应-输运-力学耦合动力学模型并编制了模拟程序。以湖南水口山矿区为例,通过动力学模拟表明不同地层岩性的断裂渗透率大小和演化特征存在显著差异,断裂作用促使岩石渗透率的空间非均匀性增强,从而有利于流体的局部汇聚和矿体的形成。断裂中压力随时间呈现出非周期振荡变化,反映了断裂演化的混沌特征。     

Architecture of fault zones determined from outcrop, cores, 3-D seismic tomography and geostatistical modeling: example from the Albalá Granitic Pluton, SW Iberian Variscan Massif

The 3-D seismic tomographic data are used together with field, core and well log structural information to determine the detailed 3-D architecture of fault zones in a granitic massif of volume 500×575×168 m at Mina Ratones area in the Albalá Granitic Pluton. To facilitate the integration of the different data, geostatistical simulation algorithms are applied to interpolate the relatively sparse structural (hard) control data conditioned to abundant but indirect 3-D (soft) seismic tomographic data. To effectively integrate geologic and tomographic data, 3-D migration of the velocity model from the time domain into the depth domain was essential. The resulting 3-D model constitutes an image of the fault zone architecture within the granitic massif that honours hard and soft data and provides an evaluation of the spatial variability of structural heterogeneities based on the computation of 3-D experimental variograms of Fracture Index (fault intensity) data. This probabilistic quantitative 3-D model of spatially heterogeneous fault zones is suitable for subsequent fluid flow simulations. The modeled image of the 3-D fault distribution is consistent with the fault architecture in the Mina Ratones area, which basically consists of two families of subvertical structures with NNE–SSW and ENE–WSW trends that displaces the surfaces of low-angle faults (North Fault) and follows their seismically detected staircase geometry. These brittle structures cut two subvertical dykes (27 and 27′ Dykes) with a NNE–SSW to N–S trend. The faults present high FI (FI>12) adjacent bands of irregular geometry in detail that intersect in space delimiting rhombohedral blocks of relatively less fractured granite (FI<6). Both structural domains likely correspond with the protolith and the damaged zone/fault core in the widely accepted model for fault zone architecture. Therefore, the construction of 3-D grids of the FI in granitic areas affected by brittle tectonics permits the quantitative structural characterization of the rock massif.     

Coal mining along the Warfield Fault, Mingo County, West Virginia: a tale of ups and downs

Mine development along a 15-mile (24 km) section of the Warfield Fault in Mingo County, West Virginia has broadened the geological understanding of the fault and its related structures. The fault has been exposed in two new road cuts, one in the northeast-trending segment at Neely Branch and one in the eastern east-trending segment at the head of Marrowbone Creek. Both exposures show a well-defined normal fault with a 45° to 55° N dip, juxtaposing sandstone/shale packages from the roof and the floor of the Coalburg seam. The fault is associated with a thin gouge zone, some drag folding, and parallel jointing. Its trace tends to run parallel to the crest of the adjacent Warfield Anticline. Based on underground mine development and detailed core drilling, the vertical offset along the fault plane ranges from a maximum of 240 ft (73 m) in the central part of the area near the structural bend to less than 100 ft (30 m) in western and eastern directions. The fault is located along the relatively steeply dipping (locally in excess of 25%) southern limb of the Warfield Anticline, and appears related to a late phase of extension involving folded Pennsylvanian strata. On a regional scale, the lithological variations across the fault do not suggest any appreciable strike-slip component.Underground room and pillar mines in the Coalburg seam north and south of the fault have been greatly impacted by the Warfield structures. Due to the combined (and opposite) effects of the folding and faulting, the northern mines are located up to 400 ft (125 m) higher in elevation than the southern ones. Overland conveyor belts connect mining blocks separated by the fault. The practical mining limit along the steep slopes toward the fault is around 15%. Subsidiary normal faults with offsets in the 5- to 15-ft (1.5–4.5 m) range are fairly common and form major roof control and production hurdles. Overall, the Warfield structures pose an extra challenge to mine development in this part of the Appalachian Coalfields.     

断层泥分形结构与断层运行特征

介绍了西秦岭北缘断裂带东段和海原断裂带西段的天然断层泥的分形方法和结果，并对断层泥的粒度分布特征与断层运动特性的关系进行了探讨。     

禾青井动水位对断层蠕动与慢地震过程的响应初析

以湖南禾青井深井水位观测的异常图象为例进行定性分析，发现动水位观测有可能直接反映出断层的滑动或断层的慢地震过程，前者可能为地下水物理参量的观测与研究提供亲折思路，后者则可能对震源物理学的发展和地震预报水平的提高具有特殊的意义。     

岩层离距图法研究沉积岩断裂发育史——以松辽盆地敖古拉断裂为例

利用断裂活动过程中留下的各种地质标记研究断裂发育史是比较困难的 ,已有的研究方法主要可归纳出七种 ,都存在局限性。岩层离距图法是以地震剖面为基础 ,将穿过断裂的各剖面上的标志层投影到沿断裂走向的铅垂面上 ,得到多组标志层的垂向断距数据 ,然后用下部各标志层的断距减去最上部标志层的断距 ,并作多轮次计算 ,直到最后的断距差近似为零或仅剩一个非零标志层。每一轮次计算代表一个活动期次 ,如果出现负值 ,则表示有构造反转。对松辽盆地敖古拉断裂作了实例计算 ,结果为该断裂发育经历了三个正断活动期和一个逆断活动期 ,与盆地区域性活动有些差别。岩层离距图法比起其他已有方法 ,可靠程度大大提高