地震动下考虑各向异性土体-盾构隧道数值模拟

针对层状土体-盾构隧道地震反应分析,引入了横观各向同性弹塑性模型,建立了横观各向同性介质的双渐近-多向透射边界条件。针对盾构隧道抗震设计的特点,基于横观各向同性弹塑性模型,研制了考虑层状土体各向异性和施工开挖效应,适合于地下结构动力计算的弹塑性动力有限元程序。在程序中对不同的材料采用了不同的本构关系和单元形式,并采用了关联流动法则和多种屈服准则,可同时进行横观各向同性土体与地下结构的平面应力、平面应变和轴对称问题的静动力有限元分析。最后,利用所研制的程序对上海地铁二号线石门一路站附近区间隧道在不同超越概率地震波输入下的地震反应进行了计算。结果表明,在层状土体-地铁盾构隧道的抗震分析中考虑土体各向异性的影响是必要的,所提出的计算模型是合理易行的。     

可控震源粘弹性波动方程有限差分模拟

在一般的地震波计算中,地球介质可以当作各向同性的完全弹性体来对待。而对地表土壤和精细观测,粘弹性介质模型比完全弹性模型更符合实际。可控震源是近年来发展起来的精确可控、安全有效的新型震源,但国内对可控震源传播动力学的研究较少。对可控震源激发的地震波在粘弹性介质中的传播,用有限差分方法进行了数值模拟,给出了Kelvin一阶粘弹性波动方程组、吸收边界条件和震源处理。提出了检波器接收信号加速度和传播距离的三次多项式指数关系式,比线性指数关系更准确。使用该公式可以预测采集系统有效接收距离,指导测线布置。      

Radial anisotropy in the crust and upper mantle beneath the Qinghai-Tibet Plateau and surrounding regions

Relative SV and SH wave speeds are generally attributed to radial seismic anisotropy which can be used as the indicator of crust/mantle deformation styles. Surface wave data were initially collected from events of magnitude Ms  5.0 and shallow or moderate focal depth occurring between 1980 and 2002: 713 of them generated Rayleigh waves and 660 Love waves, which were recorded by 13 broadband digital stations in Eurasia and India. Up to 1525 source-station Rayleigh waveforms and 1464 Love wave trains were earlier analysed by multiple filtering to obtain Love- and Rayleigh wave group velocity curves in the broad period range 10–105 s. We have performed tomographic inversion to obtain period-dependent group velocity and further shear wave velocity at 2° × 2°-sized grid-cells of a mesh covering the model region, after averaging azimuthal effects. Horizontally and vertically varying shear-wave velocities are observed, but the models of isotropic seismic velocity in the crust and upper mantle cannot fit simultaneously the inverted group-velocity dispersion curves due to the discrepancy in the transmission velocities of Love and Rayleigh waves, whose likely origin is the existence of radial anisotropy in the continental crust and topmost mantle. The strength of radial anisotropy computed from the Love–Rayleigh discrepancy and its spatial extent beneath the Qinghai-Tibet Plateau are shown as maps of percentage anisotropy at various depths down to 170 km and cross-sections along five profiles of reference. Areas in which radial anisotropy is in excess of 6% are found in the crust and upper mantle underlying most of the plateau, and even up to 10% in some places. The strength and spatial configuration of radial anisotropy seem to indicate the existence of a regime of horizontal compressive forces in the frame of the convergent Himalayan–Tibetan orogen, the laterally variation of the lithospheric rheology and the differential movement as regards the compressive driving forces.     

含煤地层各向异性介质有限差分数值模拟

煤储层是一种双重孔隙介质,其孔隙由基质孔隙和裂隙组成,并具有自身独特的割理系统。传统的煤田地震勘探将煤层假设为单一的各向同性介质,没有考虑其中裂隙对煤层的影响。利用交错网格高阶有限差分算法,分别对不同厚度VTI和HTI型煤层的弹性波传播特征进行数值模拟,获得波场快照和含煤层状介质的地震模拟记录。从波场快照中可以看出,弹性波在VTI和HTI型煤层中传播存在明显差异;煤层厚度变化对波场的敏感性要强于煤层类型的变化。      

裂缝诱导双相HTI介质模型及其弹性波传播方程

将Biot双相介质理论与Gurevich裂缝各向异性理论相结合,建立了能够同时考虑实际裂缝性储层孔隙性和各向异性的裂缝诱导双相HTI介质模型。从本构方程、动力学方程和动力学达西定律出发,推导出了裂缝诱导双相HTI介质中弹性波传播的一阶速度-应力方程,并针对方程的刚性问题,给出了利用显式二阶时间积分法数值求解该方程时所需要满足的稳定性条件。该方程能够定量地给出双相HTI介质的波场特征与裂缝参数、背景孔隙介质参数之间的关系,描述弹性波在这种介质中的传播机理。     

Elastic properties of six silicate garnet end members from accurate ab initio simulations

The elastic properties of six silicate garnet end members, among the most important rock-forming minerals, are investigated here for the first time via accurate ab initio theoretical simulations. The Crystal program is used, which works within periodic boundary conditions and allows for all-electron basis sets to be adopted. From the computed elastic tensor, Christoffel’s equation is solved along a set of crystallographic directions in order to fully characterize the seismic wave velocity anisotropy in such materials. Polycrystalline isotropic aggregate elastic properties are derived from the computed single-crystal data via the Voigt-Reuss-Hill averaging procedure. Transferability of the elastic properties from end members to their solid solutions with different chemical compositions is also addressed.     

利用高阶交错网格有限差分法数值模拟VTI介质井孔声场

横向各向同性（TI）介质是岩石地球物理中常见的一种现象,研究其井孔声场传播特征对声波测井理论以及为声波测井解释提供依据具有重要意义。针对具有垂直对称轴的横向各向同性（VTI）介质,根据柱坐标系条件下的弹性波波动方程,推导了速度-应力交错有限差分公式,采用时间二阶、空间十阶的交错有限差分算法对VTI介质中的井孔声场进行数值模拟。给出了在均匀介质中井孔声场不同时刻的波场快照,以及不同各向异性系数的VTI介质中的波场快照,计算了井轴上声源激发出的声波全波列波形。结果表明,在其他条件不变的条件下,VTI地层的各向异性系数的增大对横波的传播影响不大,但会使得纵波在纵向上的传播速度相对变小,径向上变化不大。各向异性系数的增大会使声波测井全波列首波信号时差变大,声波幅度略变小。      

Fracture-Induced Anisotropic Attenuation

The triaxial nature of the tectonic stress in the earth’s crust favors the appearance of vertical fractures. The resulting rheology is usually effective anisotropy with orthorhombic and monoclinic symmetries. In addition, the presence of fluids leads to azimuthally varying attenuation of seismic waves. A dense set of fractures embedded in a background medium enhances anisotropy and rock compliance. Fractures are modeled as boundary discontinuities in the displacement u and particle velocity v as $[{\varvec{ \kappa}}\cdot {\bf u} + {\varvec{\eta}} \cdot {\bf v} ],$ where the brackets denote discontinuities across the fracture surface, ${\varvec{\kappa}}$ is a fracture stiffness, and ${\varvec{\eta}}$ is a viscosity related to the energy loss. We consider a transversely isotropic background medium (e.g., thin horizontal plane layers), with sets of long vertical fractures. Schoenberg and Muir’s theory combines the background medium and sets of vertical fractures to provide the 13 complex stiffnesses of the long-wavelength equivalent monoclinic and viscoelastic medium. Long-wavelength equivalent means that the dominant wavelength of the signal is much longer than the fracture spacing. The symmetry plane is the horizontal plane. The equations for orthorhombic and transversely isotropic media follow as particular cases. We compute the complex velocities of the medium as a function of frequency and propagation direction, which provide the phase velocities, energy velocities (wavefronts), and quality factors. The effective medium ranges from monoclinic symmetry to hexagonal (transversely isotropic) symmetry from the low- to the high-frequency limits in the case of a particle–velocity discontinuity (lossy case) and the attenuation shows typical Zener relaxation peaks as a function of frequency. The attenuation of the coupled waves may show important differences when computed versus the ray or phase angles, with triplication appearing in the Q factor of the qS wave. We have performed a full-wave simulation to compute the field corresponding to the coupled qP–qS waves in the symmetry plane of an effective monoclinic medium. The simulations agree with the predictions of the plane-wave analysis.     

微屈多次波正演模拟及其在中原油田深层地震资料解释中的应用

对微屈多次波的压制或利用是地震资料处理、解释中的一个难题。正演模拟是压制或利用微屈多次波的基础。笔者利用层状介质非线性模型理论,发展了一种正演模拟微屈多次波的方法。利用这一方法在中原油田深层地震资料解释中作了初步应用,取得了一些有用的成果。该方法也可以在地震子波分析处理和提高地震资料分辨率中发挥作用。     

反射MT方法的伪脉冲理论

反射MT方法是一种分析MT数据的新方法,该方法与反射地震相似.本文提出了与时间域地震波脉冲响应Z变换相类似的伪脉冲响应u变换,用来分析多层介质中伪脉冲响应.该方法为MT数据的处理和解释提供了新的途径. 文章讨论了电磁波在电介性介质和导电介质中的传播特征和伪脉冲响应.对二层和三层地电模型的理论分析和数值计算表明,伪脉冲响应的u变换理论的正确性.     

利用时间分裂的错格伪谱法模拟地震波在基于改进BISQ模型的双相介质中的传播

改进的BISQ(Biot-Squirt)模型中各参数具有明确的物理意义和可实现性,在不引入特征喷流长度的情况下可将Biot流动和喷射流动两种力学机制有机地结合起来;而高精度的地震波场数值模拟技术是研究双相介质地震波传播规律的重要手段。本文从本构方程、动力学方程和动力学达西定律出发,推导了基于改进BISQ模型的双相各向同性介质的一阶速度--应力方程组;采用时间分裂错格伪谱法求该方程组的数值解,模拟半空间及层状双相介质中的地震波场。数值模拟结果表明:①与传统方法相比,时间分裂错格伪谱法波场数值模拟的精度更高,压制网格频散效果更好;②在非黏滞相界情况下,慢纵波呈传播性,而在黏滞相界情况下,慢纵波呈扩散性,以静态模式出现在震源位置;③双相介质分界面处,各类波型复杂的反射透射规律可由数值模拟结果清晰展现。     

The seismological picture of the inner core: structure and rotation

This paper presents a review of recent results concerning the structure and the rotation of the inner core, as inferred from seismological observations. We first focus on the apparent hemispherical pattern of the inner core structure, observed in both the anisotropy and the heterogeneity of the uppermost layers, whereas isotropic velocities seem to be homogeneous in a broad wavelength domain. Then we present results on the radial variations of the attenuation and its possible anisotropy, for which viscoelasticity and wave scattering provide complementary explanations. Linked to these results is a discussion about the detection of the PKJKP phase, which propagates as S-wave inside the inner core. Finally, the seismological observations of a possible inner core rotation are discussed; recent results seem to favour rotation rates below 0.2° yr^?1.     

VTI介质中的地层弹性参数反演

在VTI介质中，用非双曲线可以很好地近似P－P波中长排列情况下的旅行时；而对P－SV波来说，应用非双曲线却不能很好地近似P－SV波的施行时。对P－P波、P－SV波的旅行时进行三项泰勒展开时，它们的系数却包含了地震波的各向异性信息及其垂直速度信息，这为地震波的弹性参数反演提供了基础。实验分析表明，在中等排列长度下可以精确地得到了P－P波，P－SV波旅行时的三项泰勒展式系数，从而可以精确地进行地层弹性参数反演。     

Tectonic episodes of cratons: conflicting North American concepts

Over the past one hundred years North American geologists have been influenced by concepts of Earth history based on periodic events involving marked (‘Neocatastrophic’) changes and competing concepts involving steady-state (‘Uniformitanan’) behaviour. T.C. Chamberlin, a late 19th-/early 20th-Century exponent of a nonuniformitarian scenario of earth history, proclaimed ‘diastrophism as the ultimate basis of correlation’ - meaning that geological history is punctuated by orogenic paroxysms causing retreat of epicontinental waters to oceanic basins, creating segmentation of the stratigraphic and chronological record. At mid-Century James Gilluly gained wide support for the proposition that orogeny has followed a Uniformitarian, near-steady-state course. Accordingly, episodic diastrophism is a myth and cannot be the basis for periodic eustatic sea-level change, interregional unconformities, etc. In more recent decades two powerful new influences on geological thought have emerged. The global tectonic paradigm has forced upon us the realization that rearrangements of lithospheric plates are capable of changing the freeboard of continents. At the same time technological advances in the acquisition and processing of seismic-reflection data have been seized by receptive minds to organize the newly available stratigraphic imagery for application to the discipline of seismic stratigraphy which emphasizes the identification and correlation of unconformity-bounded successions of strata. Expansion of the methodology to the outcrop, beyond the limitations of seismic resolution, has brought about the flowering of the New Sequence Stratigraphy, doctrine that has deservedlyachieved wide application and acclaim. Practitioners of sequence stratigraphy, impressed by the distances over which unconformity-bounded stratal units can be correlated, hew to the belief that eustatic (commonly glacially engendered) sea-level change is the control. This paper examines evidence of tectonic episodes affecting cratons and their margins. These offer promise of a more satisfactory understanding of stratigraphic sequences and of the Earth history they represent. Consideration of these matters makes it inescapable that the elevation and subsidence of cratons (and their component basins and arches) reflect tectonic phenomena of the continental lithosphere quite independent of eustatic events.     

The nature of precursor waves from distant earthquakes

It is shown that, in accordance with the data used when determining velocity distribution in the Earth’s core [14], so called “precursor” earthquakes cannot be produced by wave scattering to lower mantle inhomogeneities, because seismic rays linking the earthquake sources and seismic stations are located in different inner zones of the Earth and travel at different azimuths, producing a stable wave pattern on aggregate. Thus, the present work considers the fundamental problem regarding what precursor earthquakes are. Solution of this problem will guide ideas about the structure of the Earth’s core.     

TTI介质弹性波频率-空间域有限差分数值模拟

由周期性薄互层引起的VTI介质是研究比较广泛的一类各向异性介质。当VTI介质对称轴偏离垂向,本构坐标系与观测坐标系不重合时,会形成观测坐标系下的TTI介质。引入25点优化差分算子,推导出二维TTI介质频率域弹性波动方程;为压制边界反射,采用完全匹配层法吸收边界条件,并计算出优化差分系数;最后采用集中力源,模拟了弹性波在TTI介质中的传播过程。从波场快照和地面共炮记录可以看出,笔者采用的数值模拟算法能有效压制数值频散。TTI介质中的波场传播比较复杂,纵波传播相对稳定,横波波前的三分叉现象比较明显,并存在振幅奇异性。当VTI介质的对称轴偏转后,还会增加地面地震记录的复杂性。     

地球各向异性介质中地震波动理论、检测与应用研究

地下岩石的各向异性主要表现在地震波速度随传播方向发生变化,不同类型体波间相互耦合,横波发生分裂,波速度频散依赖于传播方向等。薄互层与裂隙定向分布等产生视各向异性,它在石油地震勘探、地震预测和岩石圈物理与动力学研究中有极大潜力和应用前景,并受到广泛重视。为此,文中讨论了地震各向异性研究在解决地球科学问题中的重要性与必要性;系统地介绍了中国在地震各向异性研究领域的各个方面,如波动传播、波场激发、数值模拟、偏移与反演成像,以及应用于油气资源探测、深部地球物理研究和地质灾害监测等方面所取得的新进展。结合笔者参加的第八届地震各向异性国际学术讨论会,及ＳＥＧ,ＩＡＳＰＥＩ,ＩＵＧＧ等有关学术会议情况,综述了国际上在该领域内的主要成果与发展动向,分析了国际上各国地震各向异性研究现状及存在问题,并对我国在该领域研究的进一步开展提供了主攻问题与相应建议。     

弱各向异性介质地震波传播特征分析

随着油气田勘探精度要求越来越高,各向异性已成为不得不考虑的重要因素,因此对地震波在各向异性介质中传播特征的研究具有一定的价值。利用Thomsen提出的弱各向异性理论,通过理论模型数值计算,分析了Thomsen各向异性参数对弱各向异性VTI介质中三种体波的影响。分析结果表明:①参数ε、δ分别影响qP波大角度、中小角度传播的各向异性;②参数(ε-δ)影响qSV波中等角度传播时的各向异性;③参数γ影响qSH波大角度传播的各向异性,且群速度的各向异性要比相速度的各向异性更明显,并会出现复杂的交会区。通过这些研究分析,进一步认识了弱各向异性介质相速度及群速度随各向异性参数变化的规律。     

Calculation of vibration transmission over bedrock using a waveguide finite element model

A finite element method is developed for the study of elastic wave propagation in layered ground environments. The formulation is based on a spectral finite‐element approach using a mixture of high‐order element shape functions and wave solutions. The numerical method provides solutions to vibration transmission on and within layered elastic waveguides. Examples of its use include the theoretical analysis of transmission of vibrations in the vicinity of the surface of the ground. The mathematical model is two dimensional, and the interior of the ground is modelled as an elastic layer overlying a rigid foundation. An analysis of the natural modes of free vibration in a single layer and two layers is presented and compared with known results. In addition the forced response of the layers, for which the surface is assumed to be subjected to a harmonic point force load is shown. These results also include an illustration of the attenuation of surface vibration due to ‘wave impedance blocks’ in the ‘near field’ of the source up to a frequency of 200 Hz for two soil types. Copyright © 2007 John Wiley & Sons, Ltd.     

2-D横向各向同性介质中地震反射波几何运动学研究

先后推导了水平层与倾斜层2-D横向各向同性介质地震波反射波走时曲线方程,并就似SH波进行了模型计算,发现2-D情况下,似SH波的反射波走时曲线基本上符合双曲线形式。