共查询到15条相似文献，搜索用时 93 毫秒
1.
基于任意空间取向TI介质(简称ATI)中体波速度和偏振解析解,通过模型数值计算给出ATI介质中体波群速度和相速度的变化特征,说明TI空间取向与测线方位对速度的影响。研究表明,体波群速度图案和相速度图案相对TI对称轴固定,随TI对称轴倾角及其相对测线方位角的变化呈现出一定的对称性和重复性;可以针对ATI地区的地质情况,给出体波群速度和相速度变化图案,为进一步的理论研究提供便捷。此结果也可以直接用于VSP(垂直地震剖面)和井间地震资料的分析研究 相似文献
2.
本文基于任意空间取向TI介质中坐标变换的方法，扩展研究了任意强弱、具有任意空间取向对称轴的TI介质中体波相速度和群速度的方位变化；通过模型数值计算，获得了相速度与群速度方位变化图案，并比较了二者偏差.研究发现，各向异性越强群速度与相速度的偏差越大；并且，TI对称轴的空间取向和测线方位影响速度方位变化.相对于TI对称轴，速度方位变化图案不变；但是，随着TI对称轴空间取向和测线方位的改变，其速度方位变化呈现一定的规律性.研究结果可以精确地预测任意空间取向TI介质中速度方位变化，有利于地震各向异性数据处理与解释. 相似文献
3.
由于构造运动等作用，TI介质对称轴往往沿空间任意方向分布，具有任意空间取向对称轴的TI（ATI）介质更符合实际地质情况.VTI介质与ATI介质的相速度在形式上具有一致性，VTI介质中地震波的相角对应ATI介质对称轴与地震波传播方向的夹角.本文基于Tsvankin的VTI介质精确相速度公式，利用TI介质对称轴和地震波传播方向上单位向量的数量积和向量积来计算ATI介质的精确相速度.根据弱各向异性假设，导出qP波和qSV波的近似相速度，分析了近似公式的误差，讨论总结了ATI介质qP波和qSV波的相速度特征.本文中的单位向量采用观测坐标系表示，通过相角关系，可以较为方便地由ATI介质近似相速度导出频散关系，然后借助傅里叶逆变换推导出时间-波数域qP波和qSV波解耦的波动方程.数值算例表明本文的波动方程是qP波和qSV波解耦的，波场计算结果稳定，未出现明显的数值频散，验证了本文方法的有效性. 相似文献
4.
同类反射波（非转换波）走时偏离双曲，称为非双曲或四次时差，在长排列各向异性地震资料处理中需要校正．本文基于我们导出的水平界面任意空间取向TI (ATI)介质中同类反射波四次时差系数(A4)的精确解析解，数值计算研究P波四次时差系数特征．正演结果表明，ATI条件下A4系数随CMP测线方位变化的特征不仅与TI介质的各向异性参数有关，而且与TI对称轴的空间取向密切相关； TI介质的各向异性参数和TI对称轴的倾角决定了A4变化特征，而且TI对称轴的方位决定了A4随测线方位变化的对称性．此研究结果将对各向异性解释及参数反演有参考意义． 相似文献
5.
6.
非双曲（远偏移距）时差为各向异性介质中正、反演研究，特别是各向异性参数估计提供了重要信息.本文在任意空间取向TI（ATI）介质水平界面同类反射波四次时差系数(A4)精确解的基础上，进一步讨论我们推导得出的ATI介质中四次时差系数解析近似解，比较随CMP测线方位变化的近似解与精确解之间的差别，为利用近似解来解析研究ATI介质中非双曲时距以及参数反演提供有价值的信息．结合实际岩性资料的数值研究表明，ATI条件下四次时差系数近似解与精确解之间存在差别，不仅表现在A4数的大小及符号特征上，更突出地表现在A4系数随方位的变化特征上；在强各向异性条件下，近似解相比精确解存在较大误差．但在各向异性参数满足0<ε-δ<0.15、｜δ｜<0.20的情况下，对于TI对称轴的特殊倾角范围(75°～80°)，近似解与精确解的差别很小，可用近似解进行各向异性观测解释及参数反演． 相似文献
7.
8.
常规长排列非双曲动校正公式是在VTI介质中得到的,它不能满足任意空间取向TI(ATI)条件下的扩展.本文以VTI介质中非双曲动校正公式为基础,基于我们推导得出的ATI介质中精确四次时差系数解析解和NMO速度解析解,给出ATI介质中长排列优化的非双曲动校正公式.通过与各向异性射线追踪方法计算所得出的"精确走时"结果对比,研究表明优化后的非双曲动校正公式能精确地描述任意强弱、ATI介质中随测线方位变化的走时曲线,可以用来替代耗时、多偏移距、多方位的射线追踪方法正演拟合ATI介质中长偏移距反射走时,为利用非双曲时距的各向异性参数反演提供理论基础性认识。 相似文献
9.
10.
探讨了利用接收函数方位变化研究各向异性复杂地区速度结构的可能性. 详细介绍了具有任意对称轴方向的横向各向同性系统中介质响应的计算过程，并将利用接收函数方位变化研究地壳各向异性的方法应用于华北太行山地区. 结果表明，研究台站下方地壳具有明显的各向异性特征，其中地表盖层表现为8％——15％的慢轴型各向异性；深部地壳各向异性略小，表现为3％——5％的快轴型各向异性特征. 不同台站获得的各向异性对称轴的方向及深度分布不具有明显的一致性. 区域构造环境的变化可能是导致地壳各向异性存在的原因. 相似文献
11.
Ilya Tsvankin 《Geophysical Prospecting》1997,45(3):479-512
The transversely isotropic (TI) model with a tilted axis of symmetry may be typical, for instance, for sediments near the flanks of salt domes. This work is devoted to an analysis of reflection moveout from horizontal and dipping reflectors in the symmetry plane of TI media that contains the symmetry axis. While for vertical and horizontal transverse isotropy zero-offset reflections exist for the full range of dips up to 90°, this is no longer the case for intermediate axis orientations. For typical homogeneous models with a symmetry axis tilted towards the reflector, wavefront distortions make it impossible to generate specular zero-offset reflected rays from steep interfaces. The ‘missing’ dipping planes can be imaged only in vertically inhomogeneous media by using turning waves. These unusual phenomena may have serious implications in salt imaging. In non-elliptical TI media, the tilt of the symmetry axis may have a drastic influence on normal-moveout (NMO) velocity from horizontal reflectors, as well as on the dependence of NMO velocity on the ray parameter p (the ‘dip-moveout (DMO) signature’). The DMO signature retains the same character as for vertical transverse isotropy only for near-vertical and near-horizontal orientation of the symmetry axis. The behaviour of NMO velocity rapidly changes if the symmetry axis is tilted away from the vertical, with a tilt of ±20° being almost sufficient to eliminate the influence of the anisotropy on the DMO signature. For larger tilt angles and typical positive values of the difference between the anisotropic parameters ε and δ, the NMO velocity increases with p more slowly than in homogeneous isotropic media; a dependence usually caused by a vertical velocity gradient. Dip-moveout processing for a wide range of tilt angles requires application of anisotropic DMO algorithms. The strong influence of the tilt angle on P-wave moveout can be used to constrain the tilt using P-wave NMO velocity in the plane that includes the symmetry axis. However, if the azimuth of the axis is unknown, the inversion for the axis orientation cannot be performed without a 3D analysis of reflection traveltimes on lines with different azimuthal directions. 相似文献
12.
Weak‐anisotropy approximation for P‐wave reflection coefficient at the boundary between two tilted transversely isotropic media 
下载免费PDF全文
下载免费PDF全文 Existing and commonly used in industry nowadays, closed‐form approximations for a P‐wave reflection coefficient in transversely isotropic media are restricted to cases of a vertical and a horizontal transverse isotropy. However, field observations confirm the widespread presence of rock beds and fracture sets tilted with respect to a reflection boundary. These situations can be described by means of the transverse isotropy with an arbitrary orientation of the symmetry axis, known as tilted transversely isotropic media. In order to study the influence of the anisotropy parameters and the orientation of the symmetry axis on P‐wave reflection amplitudes, a linearised 3D P‐wave reflection coefficient at a planar weak‐contrast interface separating two weakly anisotropic tilted tranversely isotropic half‐spaces is derived. The approximation is a function of the incidence phase angle, the anisotropy parameters, and symmetry axes tilt and azimuth angles in both media above and below the interface. The expression takes the form of the well‐known amplitude‐versus‐offset “Shuey‐type” equation and confirms that the influence of the tilt and the azimuth of the symmetry axis on the P‐wave reflection coefficient even for a weakly anisotropic medium is strong and cannot be neglected. There are no assumptions made on the symmetry‐axis orientation angles in both half‐spaces above and below the interface. The proposed approximation can be used for inversion for the model parameters, including the orientation of the symmetry axes. Obtained amplitude‐versus‐offset attributes converge to well‐known approximations for vertical and horizontal transverse isotropic media derived by Rüger in corresponding limits. Comparison with numerical solution demonstrates good accuracy. 相似文献
13.
采用具有任意方向对称轴的横向各向同性介质系统，探讨了各向异性介质中接收函数表现出的横波分裂、能量偏离等特征，并系统剖析了各向异性介质对称轴方位角、倾角以及各向异性层位分布对接收函数方位变化花样的影响.太行山隆起地区是研究华北克拉通构造运动以及动力学过程的重要场所.我们以该地区JJJX台为例，介绍了利用远场接收函数研究台站下方地壳各向异性特征的方法.反演结果表明，该台站下方存在明显的来源于中、上地壳的各向异性，浅层2.4 km以内表现出强度约为10%的裂隙成因的慢轴型各向异性，裂隙面沿NNE方向展布，与该地区断层走向一致；中地壳表现出强度约为8%的晶体成因的快轴型各向异性，太行山新生代的隆起是形成晶体优势排列方向的一种可能的动力机制. 相似文献
14.
本文首先由Christoffel方程推导出黏弹性EDA介质中均匀、 非均匀P波、 SV波和SH波的相速度表达式， 然后参照极端各向异性介质的相关计算方法， 推导出EDA介质中均匀、 非均匀地震波相衰减系数和群衰减系数的表达式， 并通过数值计算分析了相速度、 相衰减系数、 群衰减系数与裂隙方位的关系. 结果表明: 均匀介质中SH波的相速度和相衰减系数均可指示裂隙的走向； 非均匀介质中SH波相衰减系数随非均匀角的增大而增大， 且其对称轴与介质对称轴的夹角也相应增加； 由于地震波振幅的衰减随岩石物理性质的变化比地震波速度的变化更为灵敏, 而且携带了更多的岩石物理性质信息， 因此可用来探明裂隙走向、 密度及含水特性， 进而应用于预测、 预防地下工程地质灾害事故. 相似文献
15.
Anisotropy in subsurface geological models is primarily caused by two factors: sedimentation in shale/sand layers and fractures. The sedimentation factor is mainly modelled by vertical transverse isotropy (VTI), whereas the fractures are modelled by a horizontal transversely isotropic medium (HTI). In this paper we study hyperbolic and non‐hyperbolic normal reflection moveout for a package of HTI/VTI layers, considering arbitrary azimuthal orientation of the symmetry axis at each HTI layer. We consider a local 1D medium, whose properties change vertically, with flat interfaces between the layers. In this case, the horizontal slowness is preserved; thus, the azimuth of the phase velocity is the same for all layers of the package. In general, however, the azimuth of the ray velocity differs from the azimuth of the phase velocity. The ray azimuth depends on the layer properties and may be different for each layer. In this case, the use of the Dix equation requires projection of the moveout velocity of each layer on the phase plane. We derive an accurate equation for hyperbolic and high‐order terms of the normal moveout, relating the traveltime to the surface offset, or alternatively, to the subsurface reflection angle. We relate the azimuth of the surface offset to its magnitude (or to the reflection angle), considering short and long offsets. We compare the derived approximations with analytical ray tracing. 相似文献