A Review of “Tectonic Faults: Agents of Change on a Dynamic Earth”

The fluvial system represents a nested hierarchy that reflects the relationship among different spatial and temporal scales. Within the hierarchy, larger scale variables influence the characteristics of the next lower nested scale. Ecoregions represent one of the largest scales in the fluvial hierarchy and are defined by recurring patterns of geology, climate, land use, soils, and potential natural vegetation. Watersheds, the next largest scale, are often nested into a single ecoregion and therefore have properties that are indicative of a given ecoregion. Differences in watershed morphology (relief, drainage density, circularity ratio, relief ratio, and ruggedness number) were evaluated among three ecoregions in eastern Oklahoma: Ozark Highlands, Boston Mountains, and Ouachita Mountains. These ecoregions were selected because of their high-quality stream resources and diverse aquatic communities and are of special management interest to the Oklahoma Department of Wildlife Conservation. One hundred thirty-four watersheds in first- through fourth-order streams were compared. Using a nonparametric, two-factor analysis of variance (α= 0.05) we concluded that the relief, drainage density, relief ratio, and ruggedness number all changed among ecoregion and stream order, whereas circularity ratio only changed with stream order. Our study shows that ecoregions can be used as a broad-scale framework for watershed management.     

六种不同变质程度煤的最大镜质组反射率与弹性参数的关系

煤镜质组反射率是评价煤阶、区分煤种的重要参数之一,在煤层气勘探与开发、采煤、化工和冶金中有着重要的应用.以往煤阶的评价单纯通过巷道和钻孔取芯的煤样实验室测试分析获得,受取样点有限限制.本文通过6种不同变质程度煤的挥发分和镜质组最大反射率的测试,配合煤样的超声弹性测量,探讨了镜质组最大反射率与地震属性参数-波速、密度和弹性模量之间的相关性.研究发现:煤镜质组最大反射率与地震属性参数均存在较好的线性正相关,其中以密度与纵波速度的相关程度最高.从而为利用煤田地震预测镜质组最大反射率,进而预测煤阶的三维立体分布提供了试验与物理依据.     

On the rheological characterisation of liquefied sands through the dam-breaking test

This paper concerns the rheological characterisation of liquefied sands as non-Newtonian Bingham fluids. For this purpose, dam-breaking laboratory tests are often executed and interpreted, offering a viable option to identify the properties of fluidised water-soil mixtures. However, limited attention has been devoted so far to clarify what variables and measurements would allow unambiguous calibration of Bingham parameters, namely, the viscosity η and the yield stress τ_y. The numerical results of parametric studies based on the particle finite element method (PFEM) are critically inspected to gain deeper insight into the problem. First, it is confirmed that multiple η − τ_y pairs may reproduce the same experimental evidence when formed by only one measurement—usually, the post–dam-breaking displacement of the bottom toe (tip) of the liquefied mass. Then, two alternative procedures are proposed for unambiguous identification of both η and τ_y: one is based on monitoring the evolving aspect ratio of the fluid mass during free, gravity-driven flow; the other relies on a slightly different dam-breaking test, also including impact against a rigid obstacle. In particular, the latter approach reduces the relevant duration of the test, reducing the possible influence of reconsolidation effects on the calibration of rheological parameters.     

构造片麻岩含义及其成因机制

构造片麻岩是地壳深部构造层次上韧性变形带主要的构造岩类型之一,其内保留了大量岩石流变特征的重要信息,在前寒武纪高级变质岩区广泛发育。构造片麻岩是由强烈塑性变形作用、变质作用和部分熔融作用共同作用形成的动力变质构造岩,是一种宏观上具有明显的强塑性流变特征而没有明显粒径减小的构造岩;在露头和手标本上以密集条带状构造和片麻状构造为特征,在微观上为典型三边平衡结构和复晶石英条带构造。熔体存在是控制影响构造片麻岩形成的主要因素之一,主要变形机制为扩散蠕变和颗粒流动,使岩石整体产生巨大应变,而单个矿物晶体不产生变形。构造片麻岩带可以分为3种不同类型：同变质期的层状构造片麻岩带、退变质期的线性构造片麻岩带和网状构造片麻岩带。     

Investigation of Coulomb stress changes in south Tibet(central Himalayas) due to the 25th April 2015 M_W 7.8 Nepal earthquake using a Coulomb stress transfer model

After M_W 7.8 Nepal earthquake occurred, the rearrangement of stresses in the crust commonly leads to subsequent damaging earthquakes. We present the calculations of the coseismic stress changes that resulted from the 25 th April event using models of regional faults designed according to south Tibet-Nepal structure, and show that some indicative significant stress increases. We calculate static stress changes caused by the displacement of a fault on which dislocations happen and an earthquake occurs. A M_W 7.3 earthquake broke on 12 May at a distance of * 130 km SEE of the M_W 7.8 earthquake, whose focus roughly located on high Coulomb stress change(CSC) site. Aftershocks(first 15 days after the mainshock)are associated with stress increase zone caused by the main rupture. We set receiver faults with specified strikes, dips,and rakes, on which the stresses imparted by the source fault are resolved. Four group normal faults to the north of the Nepal earthquake seismogenic fault were set as receiver faults and variant results followed. We provide a discussion on Coulomb stress transfer for the seismogenic fault, which is useful to identify potential future rupture zones.     

南宁膨胀土非线性剪切应力松弛特性试验

利用四联装等应变直剪仪,对南宁非饱和重塑膨胀土进行一系列室内剪切应力松弛试验,探讨南宁非饱和重塑膨胀土的剪切应力松弛特性,得到诸多有益的结论。试验结果表明,不同初始条件下的剪切应力松弛曲线均属于不完全衰减型,剪切应力逐渐减少并趋于一个稳定值;膨胀土的松弛曲线都可以明显的分成3个阶段：瞬间松弛阶段、衰减松弛阶段、稳定松弛阶段。不同初始条件下不同时刻的剪切应力-应变等时关系曲线都是非线性的曲线,说明南宁膨胀土具有明显的非线性流变特性,是弹、黏、塑性体。膨胀土的含水率越高,或者竖向荷载越小,或者初始应变越大,或者时间越长,则膨胀土的流变特性及其非线性程度就越高。对试验结果的分析,通过改进剪切应力对数与时间对数的线性关系,建立南宁膨胀土在直剪条件下的非线性剪切应力松弛经验方程,能较好地拟合试验结果。非线性经验模型考虑了应变水平对应力松弛的影响,直观地反映出南宁膨胀土的非线性应力松弛特性,更加符合工程实际,可为膨胀土非线性应力松弛问题的计算分析提供理论依据。     

利用大地测量和地热资料联合确定黑水—泉州地学断面东段岩石圈热及强度结构

黑水泉州地学断面因其所处的特殊地理位置和所受复杂地球动力学机制的影响,而备受地学界的关注.但要弄清控制岩石圈动力机制的重要影响因素之一——热动力,还需对岩石圈的热结构有更细致的研究.地热学研究作为一种独立的地球物理学方法,在地球内部结构及地球动力学研究中发挥着越来越重要的作用.根据地热资料来研究地球深部热结构是一种最为直接有效的方法,但是,我国地热资料的相对匮乏严重阻碍了地热研究的进展.本文将引入地形、重力等大地测量观测资料作为约束条件,基于岩石圈均衡原理,综合地热和重力学方法联合确定黑水泉州地学断面东段岩石圈热结构,弥补了传统地热研究方法的不足.基于黑水泉州地学断面岩石圈二维温度分布结果,本文计算了该岩石圈的强度分布,并对其岩石圈的热结构和流变结构特征展开了分析和讨论.     

True amplitude elastic Gaussian beam imaging of multicomponent walkaway vertical seismic profiling data

We develop the true‐amplitude prestack migration of multicomponent data based on the use of elastic Gaussian beams for walkaway vertical seismic profile (VSP) acquisition systems. It consists in a weighted summation of multishot data with specific weights, computed by tracing elastic Gaussian beams from each imaging point of the target area towards the sources and receivers. Each pair of beams may be connected with either a pair of P‐rays (PP‐image) or the P‐ray towards sources and the S‐ray to receivers (PS‐image) and is uniquely determined by dip (the angle of the bisector between the rays and the vertical direction) and opening (the angle between the rays) angles. Shooting from the bottom towards the acquisition system helps to avoid well‐known troubles, in particular multipathing for the imaging conditions in complex velocity models. The ability to fix the dip angle and implement summation over opening angles leads to the so‐called selective images that contain mostly interfaces with desired slopes. On the other hand, a set of images computed for a range of opening angles by summation over all available dip angles is used as input of an AVO‐like inversion procedure for the recovery of elastic parameters. The feasibility of this imaging procedure is verified by synthetic data for 2D realistic elastic models.     

湖相软土流变模型识别及其工程应用分析

对苏州湖相软土进行了三轴流变试验,根据试验结果拟采用S-6、K-B、K-S 3个流变模型来描述土体的流变特征,在模型参数反演中发现,S-6模型对加载初期变形的拟合精度不够,K-B模型对加载中期变形的拟合精度不够,而K-S模型能够很好地描述苏州湖相软土的流变特征。在模型的实际应用中引入应力比的概念,发现应力比与模型参数成指数关系,以此可以根据不同的工程应力条件来选择模型参数,最后,将该模型用于实际工程的沉降计算,通过与实测数据的对比显示模型的拟合精度较高,可以用于指导该地区的工程建设。     

Optimal implicit staggered‐grid finite‐difference schemes based on the sampling approximation method for seismic modelling

We propose new implicit staggered‐grid finite‐difference schemes with optimal coefficients based on the sampling approximation method to improve the numerical solution accuracy for seismic modelling. We first derive the optimized implicit staggered‐grid finite‐difference coefficients of arbitrary even‐order accuracy for the first‐order spatial derivatives using the plane‐wave theory and the direct sampling approximation method. Then, the implicit staggered‐grid finite‐difference coefficients based on sampling approximation, which can widen the range of wavenumber with great accuracy, are used to solve the first‐order spatial derivatives. By comparing the numerical dispersion of the implicit staggered‐grid finite‐difference schemes based on sampling approximation, Taylor series expansion, and least squares, we find that the optimal implicit staggered‐grid finite‐difference scheme based on sampling approximation achieves greater precision than that based on Taylor series expansion over a wider range of wavenumbers, although it has similar accuracy to that based on least squares. Finally, we apply the implicit staggered‐grid finite difference based on sampling approximation to numerical modelling. The modelling results demonstrate that the new optimal method can efficiently suppress numerical dispersion and lead to greater accuracy compared with the implicit staggered‐grid finite difference based on Taylor series expansion. In addition, the results also indicate the computational cost of the implicit staggered‐grid finite difference based on sampling approximation is almost the same as the implicit staggered‐grid finite difference based on Taylor series expansion.