基于槽波的TVSP超前探测方法:可行性研究

针对隧道工程中TVSP（Tunnel Vertical Seismic Profiling）方法不适合于煤矿巷道超前探测的问题,介绍了煤矿巷道中的槽波TVSP超前探测方法原理和实现过程.通过理论和数值模拟证明：（1）当采用垂向集中力源（z方向）激发地震波时,地震波场z分量受到巷道影响较小,且主要为Rayleigh型槽波,较为适合槽波超前探测;（2）采用传播相对稳定且易于识别的槽波埃里相峰值时间代替传统TVSP方法中体波的初至走时时间,能够较准确地确定断层在掌子面前方位置和断层角度;（3）当断层与巷道掘进方向夹角较大时,断层交点位置（断层线与巷道掘进方向的交点）具有很好的定位精度,但角度误差则会较大;当实际断层交点位置距离迎头较远时,断层交点位置定位精度会下降,但角度误差则影响较小;（4）基于槽波的TVSP方法对观测系统要求不高,数据处理过程简单,计算量小.     

小浪底水库区震源机制解特征

利用小浪底水库台网8个台站的地震波形数据,采用垂直向P波、S波最大振幅比和初动方法测定2009年1月—2012年12月水库区域45次小地震的震源机制。结果表明:该区域45次震源机制中正断层13次、逆断层15次,走滑断层17次;主压应力轴(P轴)总体为NEE方向(220°～230°),与华北地区近水平构造应力场不完全一致,显示了小浪底水库区域受华北构造应力场的控制作用较弱,应该与水库区域地下介质构造复杂和水库蓄水有关。     

与构造有关和应力引起的剪切波速度各向异性：加州中部卡拉韦拉斯断层附近微震的观测结果

试图利用1986年1月26日加利福尼亚特雷斯皮诺斯地震（M5.5)前后发生的微震（M≤2.6)来区分与上地壳构造相关及应力引起的剪切波速度的各禹异性，特雷斯皮诺斯地震发生在昆萨贝断层上，此断层位于加利福尼亚中部，在卡拉韦拉斯断层东部约10km处，是一个北西-南东走向的右旋走滑断层，昆萨贝牧场台站（HQR）1984年-1992年的数字式三分量地震图可用来进行分析。该台站位于主震震中北北东方向仅7.3km处。我们使用互相关技术和质点运动图相结合的方法研究了偏振方向和延迟时间，为了提高数据分析的可信度，我们通过联合震源定位和互相关技术对震源重新定位，这样就降低了和震源位置有关的误差，在研究区里，我们发现两个地带有不同但却稳定的偏振方向。在昆萨贝断层系周围，30多个微震的剪切波偏振方向清楚地显示，慢剪切波方向正交于这个垂直右旋走滑断层的北西-南东走向。因此，速度各向异性看来是由该断层系本身造成的，但是和东边4km附近的一群微震有关的各向异性却有所不同，在这个地带，快，慢剪切波偏振方向分别和最大，最小水平应力方向相关。因此，这种地壳速度各向异性看来是由地壳中的应力状态所控制的，在一个台站对这两种偏振方向的观测表明，HQR台站下的浅层地壳对剪切波的偏振方向没有影响。     

汶川地震断裂带东北端浅部结构的人工地震探测

结合汶川地震断裂带动态监测,利用快速响应探测系统,开展了断层带浅部结构人工地震探测.针对地震断裂带动态监测条件下的复杂波场和低信噪比的情况,在f-k波场分离的基础上,分别利用了折射波共中心点成像、面波速度反演、反射波叠加成像方法,进行了浅层断层和构造成像处理,并对处理结果进行了综合解释,给出了断裂带浅部断层分布和速度特征.为汶川地震龙门山断裂带东北端动态监测提供了基础结构信息,所发展的断裂带快速响应探测技术对于地震应急动态监测具有重要意义.     

利用莫霍面Ps震相研究中国东北地区地壳各向异性

利用中国东北地区布设的65套宽频带数字地震仪2009年6月—2011年6月记录的远震事件, 用时间域最大熵谱反褶积方法提取接收函数, 并用改进的剪切波分裂分析方法对该区地壳介质各向异性参数进行研究, 获得了该区地壳介质各向异性图像. 结果表明, 该区地壳介质各向异性快波偏振方向大致为北西向, 快慢波时间延迟在0.15—0.3 s之间; 但有7个台站下方地壳各向异性快波方向表现为北东向, 可能与当地复杂构造有关. 该区地壳各向异性快波偏振方向与主压应力场方向近乎垂直, 与板块移动方向基本一致, 与SKS/SKKS各向异性快波方向也基本一致. 推断本研究区地壳介质各向异性反映了该区的主张应力方向, 且主要各向异性来源于中下地壳, 暗示了壳-幔垂直变形的一致性.      

鄂尔多斯块体西侧地壳各向异性初步研究

利用宁夏区域台网记录的2009年1月至2014年9月的近场小震波形资料, 使用剪切波分裂系统分析方法SAM方法, 对位于青藏高原东北缘的鄂尔多斯块体西侧进行了地壳各向异性研究, 共得到7个台站记录到的19条有效数据。 研究发现, 受复杂的局部构造、 应力场及断裂分布的影响, 研究区地壳各向异性在空间分布上呈现出分区性特点。 受区域构造应力场的控制, 台站的快剪切波偏振方向与区域构造应力的主压应力方向基本一致。 在构造上, 大致以中部的三关口—牛首山NNW向断裂为界, 可以分为南北两部分。 本研究显示, 以快剪切波偏振方向空间分布特征为划分依据, 大致以37°N为界划分南北部, 北部区域的快剪切波偏振方向为近N-S向, 与按构造划分的青藏高原东北缘—鄂尔多斯块体西侧北部区域主压应力场一致; 南部区域的快剪切波偏振方向为近E-W向, 同样与按构造划分的区域主压应力场一致。     

首都圈东南部地区地壳介质各向异性

基于首都圈地震台网2002——2005年的区域地震波形数据,采用剪切波分裂系统分析方法（SAM）, 计算得到首都圈东南部地区(38.5deg;N——39.85deg;N,115.5deg;E——118.5deg;E)24个台站的剪切波分裂参数. 结果表明,首都圈东南部地区快剪切波平均偏振方向与区域最大主压应力方向相近,与华北地区GPS主压应变测量结果一致;但首都圈东南部盆地地区的剪切波分裂观测结果与首都圈西北部的隆起——盆地构造结合区的观测结果不同. 这说明了不同的构造对观测结果具有一定的影响. 研究还表明,台站附近的断层分布状态对观测结果影响很大,复杂的断层分布会加剧剪切波分裂测量结果的离散程度. 本研究区域南部台站与北部台站的快剪切波偏振方向存在较大差异,这可能与该区南北部的构造及应力环境存在较大差异有关.       

中国地震科学台阵两期观测资料近场记录揭示的南北地震带地壳剪切波分裂特征

利用中国地震科学台阵第一期(2011-01-2014-06)及部分中国地震科学台阵第二期(2013-02-2015-12)的流动地震台阵记录到的小震波形资料,运用剪切波分裂系统分析(SAM)方法,分析南北地震带的地壳各向异性,对剪切波分裂参数所反映的区域应力环境及构造特征,以及区域内主压应力方向与断裂分布的关系展开讨论.研究结果表明,南北地震带快剪切波偏振方向自北向南由NE向逐渐转变为NNW向,与南北地震带区域主压应力的方向变化具有一致性.区域内分布的大量NE及WNW或NW向断裂构造同样对快波偏振方向有比较大的影响,位于走滑断裂附近的台站,其快波方向与断裂走向大致平行,部分位于走滑断裂附近的台站其快波方向几乎垂直于断裂走向,而与构造应力场方向一致性较好.个别台站表现出复杂快波优势方向特征,反映出研究区内构造环境的复杂性.慢波时间延迟结果显示,南北地震带南段的平均时间延迟高于北段,反映了受印度板块和欧亚板块的碰撞挤压作用,南段地壳介质各向异性程度更大,构造变形更加剧烈.对比南北地震带上地幔各向异性特征,推测在川滇菱形块体内部可能存在复杂的壳幔耦合现象,地壳剪切波分裂除了反映区域应力特征,还可以揭示出区域构造信息.     

2013年8月德钦—得荣M_S 5.9地震序列S波分裂

2013年8月28日、31日云南德钦、四川得荣交界地区分别发生M_S 5.2、M_S 5.9地震,采用纵横比与偏振分析相结合的方法,测定此次地震序列S波分裂参数,即快波偏振方向和慢波延迟时间。BZL流动地震台得到272对S波分裂参数,等面积玫瑰图显示快波优势方向为NWW向,与台站附近断层走向和地震序列分布长轴方向一致;在M_S 5.9地震发生后,快波偏振方向出现紊乱现象;观测到在M_S 5.9地震发生的前一天慢波延迟时间迅速下降,表明较大地震发生前地壳应力突然释放。     

断层衍射波及其应用ht

本文从衍射波的物理定义出发,简化了Trorey提出的断层上Kirchhoff-Helmholtz衍射方程的解法;计算了不同深度、不同测线方向下的断层衍射波理论地震图;计算了衍射波振幅谱与相位谱,给出了利用衍射波求断层位置的公式;得出了一些新的结论,通过人工地震测深与地震勘探的实例,对断层衍射波的特性有了更明确的认识。 本文的结果表明:断层衍射波发生在地球介质剧烈变化处;衍射点两侧的衍射波走时曲线呈双曲线状;波初动清晰且半周期小;其优势频率振幅谱与反射波的相同,在衍射波与反射波走时曲线相切处附近,记录图中出现衍射波最大振幅,且波反相;视断点与真实断点一般不重合。上述特点可能为判定衍射波并确定断层位置提供判据。      

Electromagnetic evidence for lateral inhomogeneities within the Earth's upper mantle

The composition of the upper mantle is of great significance to our understanding of plate tectonics and global evolution. Information about the physical properties of the Earth at upper mantle depths, including lateral variations in electrical conductivity, can be deduced from measurements of the electric and magnetic fields at the Earth's surface. Electromagnetic methods appear to give poorer resolution than do some other methods, for example seismics, but as they are sensitive to quite different properties of a medium they provide a different and complementary class of information.The basic theory of electromagnetic sounding methods is briefly reviewed below, and evidence regarding lateral conductivity inhomogeneities in the Earth's upper mantle is examined. While lateral electrical conductivity inhomogeneities appear to be the rule rather than the exception, the interpretation of electromagnetic data still presents difficulties and the results from many regions are not as yet unambiguous. Where the data are of sufficient resolution, a rapid increase in electrical conductivity can usually be identified within the upper mantle. The depth to this highly conductive zone is different in different tectonic environments, but is broadly consistent between analogous but widely separated tectonic environments. A comparatively shallow conducting region is found beneath the ocean lithosphere. The depth of this region is dependent on lithospheric age. Many of the more shallow conducting regions in both continental and oceanic environments are associated with high heat flow values and seismic low velocity zones. These highly conducting regions may be zones of partial melt.     

Seismic imaging of deep hydrocarbon reservoirs

This paper examines those aspects of reflection seismology which require special consideration when imaging deeper hydrocarbon reservoirs, including the constraints imposed by vertical resolution, lateral resolution, and velocity analysis. We derive quantitative expressions relating the uncertainties in stacking velocities and in interval velocities derived from stacking velocities to acquisition parameters, as well as expressions for the lateral resolution which can theoretically be achieved for migrated seismic images. This analysis shows that the most significant limitations of seismic imaging at depth involve the finite lateral resolution of the seismic method, and the proper lateral positioning of seismic images. These difficulties are overcome in large measure through the proper migration of a seismic dataset, which becomes more critical as deeper horizons are imaged. If these horizons are suspected of having significant 3-D structure, a strong argument may be made for acquiring a 3-D seismic survey over the prospect. Migration of this dataset will then generate an image of the subsurface with good lateral resolution in both the X and Y directions.     

A cellular model of river meandering

River meandering has been successfully modelled using vector based methods, but these can not simulate multiple or braided channels. Conversely, cellular braided river models fail to replicate meandering. This paper describes a new method to simulate river meandering within a cellular model (CAESAR). A novel technique for determining bend radius of curvature on a cell by cell basis is described, that importantly allows regional information on bend curvature to be transferred to local points. This local curvature is then used to drive meandering and lateral erosion through two methods. Key difficulties are identified, including the deposition of material on point bars and cut off development, but the method illustrates how meandering can be integrated within a cellular framework. This demonstrates the potential to produce a single model that can incorporate both meandering and braiding. Copyright © 2006 John Wiley & Sons, Ltd.     

On the theory of translationally invariant magnetohydrodynamic equilibria with anisotropic pressure and magnetic shear

We present an improved formalism for translationally invariant magnetohydrodynamic equilibria with anisotropic pressure and currents with a field aligned component. The derivation of a Grad-Shafranov type equation is given along with a constraint which links the shear field to the parallel pressure. The difficulties of the formalism are discussed and various methods of circumventing these difficulties are given. A simple example is then used to highlight the methods and difficulties involved.     

A finite element method for the diffusion-convection equation with constant coefficients

Existing numerical methods for the solution of the diffusion-convection equation are unsatisfactory for convection dominated flow problems. A new finite element method incorporating the method of characteristics for the solution of the diffusion-convection equation with constant coefficients in one spatial dimensions is derived. This method is capable of solving diffusion-convection equation without any of the difficulties encountered in the existing numerical methods for the whole spectrum of dispersion from pure diffusion, through mixed dispersion, to pure convection. Several examples for the one-dimensional case are solved and results are compared with the exact solutions. The generalization of the method to variable coefficients and to the diffusion-convection equation in two space dimensions are discussed.     

Simulating meander evolution of the Geul River (the Netherlands) using a topographic steering model

Active meandering rivers are capable of reworking and removing large quantities of valuable land. Therefore, understanding the characteristics of meandering rivers and predicting future meander behaviour can be of great value for local authorities. In this study, we apply a topographic steering meander model to the Geul River (southern Netherlands), using field data to calibrate the model. The present channel characteristics of the Geul River were mapped in the field. Cut‐banks were classified as erosive, unstable or stable. The model outcomes were compared with these field data. Several model runs were carried out, using different sets of parameter values. After studying the results and using the field data, we introduced the concept of a variable channel width in the simulation model. In reality, the river has different channel widths varying from 8 to more than 15 m. These widths are a linear function of local curvature. The model runs using a variable channel width show that the model is capable of predicting locations of lateral migration in conformity with observed active lateral migration and erosive banks. With both models, the sediment reworking time of the floodplain can be calculated. Floodplain reworking times of 200–300 years were calculated. In combination with the lateral migration rate, this reworking time is an important element in catchment sediment budget calculations. Copyright © 2007 John Wiley & Sons, Ltd.     

Signal detectability of marine electromagnetic methods in the exploration of resistive targets

We compare selected marine electromagnetic methods for sensitivity to the presence of relatively thin resistive targets (e.g., hydrocarbons, gas hydrates, fresh groundwater, etc.). The study includes the conventional controlled‐source electromagnetic method, the recently introduced transient electromagnetic prospecting with vertical electric lines method, and the novel marine circular electric dipole method, which is still in the stage of theoretical development. The comparison is based on general physical considerations, analytical (mainly asymptotic) analysis, and rigorous one‐dimensional and multidimensional forward modelling. It is shown that transient electromagnetic prospecting with vertical electric lines and marine circular electric dipole methods represent an alternative to the conventional controlled‐source electromagnetic method at shallow sea, where the latter becomes less efficient due to the air‐wave phenomenon. Since both former methods are essentially short‐offset time‐domain techniques, they exhibit a much better lateral resolution than the controlled‐source electromagnetic method in both shallow sea and deep sea. The greatest shortcoming of the transient electromagnetic prospecting with vertical electric lines and marine circular electric dipole methods comes from the difficulties in accurately assembling the transmitter antenna within the marine environment. This makes these methods significantly less practical than the controlled‐source electromagnetic method. Consequently, the controlled‐source electromagnetic method remains the leading marine electromagnetic technique in the exploration of large resistive targets in deep sea. However, exploring laterally small targets in deep sea and both small and large targets in shallow sea might require the use of the less practical transient electromagnetic prospecting with vertical electric lines and/or marine circular electric dipole method as a desirable alternative to the controlled‐source electromagnetic method.     

Use of Picard and Newton iteration for solving nonlinear ground water flow equations

This study examines the use of Picard and Newton iteration to solve the nonlinear, saturated ground water flow equation. Here, a simple three-node problem is used to demonstrate the convergence difficulties that can arise when solving the nonlinear, saturated ground water flow equation in both homogeneous and heterogeneous systems with and without nonlinear boundary conditions. For these cases, the characteristic types of convergence patterns are examined. Viewing these convergence patterns as orbits of an attractor in a dynamical system provides further insight. It is shown that the nonlinearity that arises from nonlinear head-dependent boundary conditions can cause more convergence difficulties than the nonlinearity that arises from flow in an unconfined aquifer. Furthermore, the effects of damping on both convergence and convergence rate are investigated. It is shown that no single strategy is effective for all problems and how understanding pitfalls and merits of several methods can be helpful in overcoming convergence difficulties. Results show that Picard iterations can be a simple and effective method for the solution of nonlinear, saturated ground water flow problems.     

地震偏移的最优可分近似算法实现

针对地震偏移算法中单程波算子的特征函数近似，采用最优可分表示法将该特征函数展开为空间变量(g)和水平波数(k)的可分表达式，以此可分近似表达式为基础，运用正反Fourier变换重新构造单程波算子. 为了克服特征函数最优可分近似计算在奇点及其领域产生的数值振荡，引入等价黏性技巧以增强算法的数值计算稳定性，并采用分频最优可分及对空间变量(g)线性插值的方法，不仅提高了计算精度，也节约计算机时. 文中具体研究了单程波算子的脉冲响应和二维叠前深度偏移. 结果表明，在不甚大步长情况下，本文构造的算子具有适应横向强变速的能力，运用Marmousi模型验证了本文方法适合复杂构造的成像.     

单程波方程偏移算子高阶辛格式

针对地震偏移算法中单程波算子中e指数项的近似，提出一种高阶辛格式算法. 与非辛格式的近似、一阶辛格式近似和两步法进行数值对比表明，文中提出的高阶辛格式具有更高的精度. 脉冲响应的计算也表明文中的近似方法具有降低频散效应和适应横向变速的能力. 用Marmousi模型验证了对复杂构造的成像的能力，实际资料计算表明本文方法适合于较大深度的稳定准确成像.