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地壳介质剪切波分裂研究的部分进展 总被引：1，自引：0，他引：1
剪切波穿过各向异性介质传播时会发生分裂现象,而在地壳中产生各向异性的主要因素是大量充满液体的定向排列的微裂隙。通过剪切波分裂参数可以研究地壳介质的特性、地壳应力状态及应力场的变化,并可用于地震预测。利用地壳介质各向异性特征研究断层性质也是一个新的动向。 相似文献
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针对PTL介质中存在定向排列的铅垂裂隙系统的组合模型,探讨在长波长情况下其等效正交各向异性弹性常数的计算方法.根据Backus方法并结合Hudson微裂隙理论,推出了PTL与EDA组合之等效正交各向异性弹性常数的计算公式,且在裂隙呈稀疏分布的假设前提下,导出了等效弹性常数的具体计算表达式,并进而用伪谱法对含垂直裂隙PTL介质的弹性波场进行了数值模拟.本文的理论研究及数值计算结果表明:用5个长波长等效PTL弹性常数和3个无量钢的裂隙柔量,就可描述等效正交各向异性介质九个独立的弹性常数. 相似文献
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针对PTL介质中存在定向排列的铅垂裂隙系统的组合模型，探讨在长波长情况下其等效正交各向异性弹性常数的计算方法。根据Backus方法并结合Hudson微裂隙理论，推出了PTL与EDA组合之等效正交各向异性弹性常数的计算公式，且在裂隙呈稀疏分布的假设前提下，导出了等效弹性常数的具体计算表达式，并进而用伪谱法对含垂直裂隙PTL介质的弹性波场进行了数值模拟。本文的理论研究及数值计算结果表明：用5个长波长等效PTL弹性常数和3个无量钢的裂隙柔量，就可描述等效正交各向异性介质力个独立的弹性常数。 相似文献
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由三分量数字地震仪组成的小孔径流动台网记录了1982年10月19日河北卢龙Ms=6.1级地震的部分余震.用质点运动图的方法对横波的偏振进行了分析。研究结果表明,在横波窗内的各观测点都存在横波的分裂现象.不同离源角和方位角快波偏振的水平投影都具有近NE40°方向的优势取向,与根据卢龙地震两组断层错动在各向同性介质中所辐射的横波的偏振方向不一致.这可以由传播介质中应力所导致裂隙的定向排列来解释.这一观测结果提供了卢龙地区脆性上地壳大范围膨胀各向异性（EDA）的证据,并表明这一地区直立平行排列裂隙取向和水平主压应力的方向为NE40°. 相似文献
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平面波分解法是研究地震波场简捷有效的方法,各种复杂的波场可用平面波合成的方法得到．文中采用平面波方法研究非均匀各向异性介质中的弹性波．对时空域非均匀各向异性介质波动方程,运用f-k变换,可得到频率空间域波动方程(Christoffel方程)．利用非均匀各向异性介质中,弹性参数及其空间变化率与Christoffel矩阵元素关系,提出非均匀各向异性介质Christoffel矩阵方程的求解方法,并运用于非均匀TIV介质和非均匀EDA介质．在连续介质条件下,当波沿速度增加方向传播时,振幅的方向导数小于零,即振幅衰减;当波沿速度减小方向传播时,振幅的方向导数大于零,即振幅增强．波的振幅强度是传播方向的函数(各向同性条件下也是如此),但并不总是衰减．若只研究波沿速度增加方向传播的情况即得出波在连续介质中传播振幅衰减的结论是不全面的． 相似文献
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一、引言在地震学文献中,各向异性和地震各向异性意指具有竖直对称轴的横向各向同性以及在性质上具有方位变化的一般定向各向异性对称系统。地震波在各向同性介质中与在横向各向同性介质中的特性之间具有许多类似之处,在这两种情况下,径向平面中的波动(P,SV 和瑞雷波动)与层状平面结构中的水平横向运动(SH 和洛夫波动)解耦;在这些结构中,地震波的传播性质可以用相当简单的解析表达式来描述。而在性质上具有方位变化的一般定向各向异性介质中,地震波的传播性质要复杂得多,这时径向运动与水平横向运动互相影响,波动性质需以方向余弦的复杂函数描述。各向 相似文献
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地下介质中普遍存在着各向异性,当前基于各向异性的地震波射线追踪多是在弱各向异性介质中进行且采用群速度近似表示方法,这些近似方法在强各项异性介质中会导致很大误差而无法真正模拟地震波的传播规律。根据地下普遍存在各向异性的事实和地震波基本传播规律,提出利用牛顿迭代法高效求解群速度,基于Paraview平台自动化构建三维地质模型,采用最短路径法进行地震波射线追踪模拟及可视化,实现对复杂三维地质的速度不均匀性和各向异性的表达,为三维地质模型的构建和地震波射线追踪模拟及可视化提供一种新思路,并以华北克拉通山西断陷带北部局部区域为例进行研究。结果表明,该方法能够减少由各向异性对地震波传播模拟造成的影响,清晰表达了研究区地质结构和各向异性特点,在对复杂三维地质结构的解读中能够较好应用。 相似文献
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Estimating azimuthal stress‐induced P‐wave anisotropy from S‐wave anisotropy using sonic log or vertical seismic profile data 
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下载免费PDF全文 Most sedimentary rocks are anisotropic, yet it is often difficult to accurately incorporate anisotropy into seismic workflows because analysis of anisotropy requires knowledge of a number of parameters that are difficult to estimate from standard seismic data. In this study, we provide a methodology to infer azimuthal P‐wave anisotropy from S‐wave anisotropy calculated from log or vertical seismic profile data. This methodology involves a number of steps. First, we compute the azimuthal P‐wave anisotropy in the dry medium as a function of the azimuthal S‐wave anisotropy using a rock physics model, which accounts for the stress dependency of seismic wave velocities in dry isotropic elastic media subjected to triaxial compression. Once the P‐wave anisotropy in the dry medium is known, we use the anisotropic Gassmann equations to estimate the anisotropy of the saturated medium. We test this workflow on the log data acquired in the North West Shelf of Australia, where azimuthal anisotropy is likely caused by large differences between minimum and maximum horizontal stresses. The obtained results are compared to azimuthal P‐wave anisotropy obtained via orthorhombic tomography in the same area. In the clean sandstone layers, anisotropy parameters obtained by both methods are fairly consistent. In the shale and shaly sandstone layers, however, there is a significant discrepancy between results since the stress‐induced anisotropy model we use is not applicable to rocks exhibiting intrinsic anisotropy. This methodology could be useful for building the initial anisotropic velocity model for imaging, which is to be refined through migration velocity analysis. 相似文献
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Perturbation methods are common tools for describing wave propagation in weakly anisotropic media. The anisotropic medium is replaced by an average isotropic medium where wave propagation can be treated analytically and the correction for the effect of anisotropy is computed by perturbation techniques. This works well for anisotropies of up to 10%. Some materials (e.g. shales), however, can exhibit a much stronger anisotropy. In this case a background is required which still can be treated analytically but is applicable to stronger P-wave anisotropy. We present an averaging technique to compute a best-fitting ellipsoidal medium to an arbitrary anisotropic medium. Ellipsoidal media are sufficiently simple for analytical expressions to be available for many applications and allow consideration of strong P-wave anisotropy. The averaging of the arbitrary anisotropic medium can be carried out globally (i.e. for the whole sphere) or sectorially (e.g. for seismic waves propagating predominantly in the vertical direction). We derive linear relationships for the coefficients of the ellipsoid which depend on the elastic coefficients of the anisotropic medium. We also provide specifications for best-fitting elliptical and best-fitting isotropic media. Numerical examples for different rocks demonstrate the improved approximation of the anisotropic model obtained using the formulae derived, compared with the conventionally used average isotropic medium. 相似文献
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提出了利用人工爆破P波走时反演地壳介质方位各向异性参数的方法. 在假定介质是弱各向异性介质的情况下, 使用扰动理论得到了线性化的反演公式, 其中待反演的弱各向异性参数是P波走时的线性函数. 如果在反演公式中参考走时取相同震中距接收点的P波平均走时, 那么所获得的弱各向异性参数与参考介质速度的选取无关. 反演得到的弱各向异性参数可以看作是不同震中距和不同深度范围内介质的等效弱各向异性参数. 等效弱各向异性参数在一定程度上反映了不同深度范围内水平方向相速度随方位的变化. 这种变化可能是不同时期构造应力作用的结果. 2007年中国地震局在首都圈怀来地区实施了一次大吨位人工爆破实验, 以爆破点为中心, 布设了高密度的地震观测台网和台阵. 台站相对于爆破点具有360°的全方位覆盖, 所得到的地震记录数据为研究怀来、 延庆地区地壳介质P波方位各向异性提供了必要条件. 我们通过走时反演获得了与水平方位相关的弱各向异性参数, 并对弱各向异性参数进行坐标变换, 得到了能够直观描述岩石弱各向异性的具有水平对称轴的横向各向同性介质, 给出了对应的3个独立弱各向异性参数及其对称轴方位, 讨论了介质各向异性与构造应力场的关系. 结果表明该地区地壳介质存在明显的方位各向异性, 其最大值约为4.6%. 相似文献
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Di Luo Zhiqiang Wu Tianjiu Zeng Xunhua Zhang Weina Zhao Huaishan Liu Guolin Xiao 《Studia Geophysica et Geodaetica》2018,62(3):466-484
The South Yellow Sea is a superimposed basin overlying Mesozoic-Cenozoic continental sediments, which in turn overlie Paleozoic-Mesozoic marine deposits that are now the target of hydrocarbon exploration. Strongly modified by multiple tectonic events, the marine sediments feature a large tectonic relief, with obvious horizontal anisotropy in seismic velocity, which significantly affects the seismic image quality. In this study, the sedimentary velocity anisotropy and its influence on image quality were analyzed using an analytical theory method, assuming transversely isotropic medium with vertical axis of symmetry (VTI), and using seismic and well-log data. Additionally, an anisotropic prestack time migration was used for the imaging of the field data. The results showed that the anisotropic pre-stack time migration processing could be used to significantly improve the accuracy of the seismic images in areas with distinct faults, offering clear images of accurately located fault planes and fault edges, thereby improving the lateral resolution of the seismic data and its signal-to-noise ratio. 相似文献
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Elastic wave propagation in inhomogeneous anisotropic media 总被引：1，自引：0，他引：1
XIU CHENG WEI ) MIN YU DONG ) YUN YAI CHEN ) ) Geoscience Department University of Petroleum Beijing China ) Institute of Geophysics China Seismological Bureau Beijing China 《地震学报(英文版)》1998,11(6):655-667
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Seismic amplitude variation with offset and azimuth (AVOaz) inversion is well known as a popular and pragmatic tool utilized to estimate fracture parameters. A single set of vertical fractures aligned along a preferred horizontal direction embedded in a horizontally layered medium can be considered as an effective long-wavelength orthorhombic medium. Estimation of Thomsen’s weak-anisotropy (WA) parameters and fracture weaknesses plays an important role in characterizing the orthorhombic anisotropy in a weakly anisotropic medium. Our goal is to demonstrate an orthorhombic anisotropic AVOaz inversion approach to describe the orthorhombic anisotropy utilizing the observable wide-azimuth seismic reflection data in a fractured reservoir with the assumption of orthorhombic symmetry. Combining Thomsen’s WA theory and linear-slip model, we first derive a perturbation in stiffness matrix of a weakly anisotropic medium with orthorhombic symmetry under the assumption of small WA parameters and fracture weaknesses. Using the perturbation matrix and scattering function, we then derive an expression for linearized PP-wave reflection coefficient in terms of P- and S-wave moduli, density, Thomsen’s WA parameters, and fracture weaknesses in such an orthorhombic medium, which avoids the complicated nonlinear relationship between the orthorhombic anisotropy and azimuthal seismic reflection data. Incorporating azimuthal seismic data and Bayesian inversion theory, the maximum a posteriori solutions of Thomsen’s WA parameters and fracture weaknesses in a weakly anisotropic medium with orthorhombic symmetry are reasonably estimated with the constraints of Cauchy a priori probability distribution and smooth initial models of model parameters to enhance the inversion resolution and the nonlinear iteratively reweighted least squares strategy. The synthetic examples containing a moderate noise demonstrate the feasibility of the derived orthorhombic anisotropic AVOaz inversion method, and the real data illustrate the inversion stabilities of orthorhombic anisotropy in a fractured reservoir. 相似文献
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裂缝诱导的双相具有水平对称轴的横向各向同性(HTI)介质模型是由一组平行排列的垂直裂缝嵌入到统计各向同性的流体饱和多孔隙岩石中而组成的,它综合考虑了裂缝型储层岩石的各向异性和孔隙性.高精度的地震波场数值模拟技术是研究该介质中地震波传播规律的主要方法.本文结合错格伪谱法和时间分裂法,求解描述该介质中地震波传播的一阶速度-应力方程.模拟了单层和双层模型中的地震波场,并对其进行了特征分析.研究结果表明:错格伪谱法能有效消除标准网格伪谱法波场模拟结果中出现的数值伪影现象,与时间分裂法结合能够获得稳定的、高精度的模拟结果;裂缝诱导双相HTI介质中的地震波场兼具裂缝各向异性介质和双相介质中传播的地震波的波场特征. 相似文献
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The conventional intersection method for earthquake location in isotropic media is developed in the case of transversely isotropic
media with a tilted symmetry axis (TTI media). The hypocenter is determined using its loci, which are calculated through a
minimum travel time tree algorithm for ray tracing in TTI media. There are no restrictions on the structural complexity of
the model or on the anisotropy strength of the medium. The location method is validated by its application to determine the
hypocenter and origin time of an event in a complex TTI structure, in accordance with four hypotheses or study cases: (a)
accurate model and arrival times, (b) perturbed model with randomly variable elastic parameter, (c) noisy arrival time data,
and (d) incomplete set of observations from the seismic stations. Furthermore, several numerical tests demonstrate that the
orientation of the symmetry axis has a significant effect on the hypocenter location when the seismic anisotropy is not very
weak. Moreover, if the hypocentral determination is based on an isotropic reference model while the real medium is anisotropic,
the resultant location errors can be considerable even though the anisotropy strength does not exceed 6.10%. 相似文献