共查询到20条相似文献,搜索用时 15 毫秒
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大陆动力学已经成为当今固体地球物理各领域研究的主导方向。大陆动力学涉及问题非常广泛,但核心问题是大陆形变及其动力学。地震各向异性是地球动力学过程的指示器,根据地震各向异性的研究结果,可以推断上地幔物质的流动或变形,有助于了解地球内部的应力状态和地球的演化过程。 相似文献
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Myung Hoon Kim Yunseok Choi Young Ho Cha Changsoo Shin 《Pure and Applied Geophysics》2009,166(12):1967-1985
In order to correctly interpret marine exploration data, which contain many elastic signals such as S waves, surface waves and converted waves, we have developed both a frequency-domain modeling algorithm for acoustic-elastic coupled media with an irregular interface, and the corresponding waveform inversion algorithm. By applying the continuity condition between acoustic (fluid) and elastic (solid) media, wave propagation can be properly simulated throughout the coupled domain. The arbitrary interface is represented by tessellating square and triangular finite elements. Although the resulting complex impedance matrix generated by finite element methods for the acoustic-elastic coupled wave equation is asymmetric, we can exploit the usual back-propagation algorithm used in the frequency domain through modern sparse matrix technology. By running numerical experiments on a synthetic model, we demonstrate that our inversion algorithm can successfully recover P- and S-wave velocity and density models from marine exploration data (pressure data only). 相似文献
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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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主要讨论了应力变化如何影响各向异性介质中波速度的问题。推导了一般各向异性介质在初始应力下的Christoffel方程,得到介质中3种波的相速度和初始应力的关系表达式;通过实验数据验证了单轴应力能够诱导各向异性,当施加单轴应力时,速度在沿应力的方向增加最大,在垂直应力的方向增加最小,实验结果与理论推导一致;用Christoffel方程的数值解模拟在3种对称情况下的弹性各向异性介质中初始应力对波速度的影响。数值结果表明:初始应力对各向异性介质中波传播速度的影响,随着各向异性强度的增加而增大,而且速度越慢,影响越大。 相似文献
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Peidong Shi Doug Angus Andy Nowacki Sanyi Yuan Yanyan Wang 《Surveys in Geophysics》2018,39(4):567-611
Seismic anisotropy which is common in shale and fractured rocks will cause travel-time and amplitude discrepancy in different propagation directions. For microseismic monitoring which is often implemented in shale or fractured rocks, seismic anisotropy needs to be carefully accounted for in source location and mechanism determination. We have developed an efficient finite-difference full waveform modeling tool with an arbitrary moment tensor source. The modeling tool is suitable for simulating wave propagation in anisotropic media for microseismic monitoring. As both dislocation and non-double-couple source are often observed in microseismic monitoring, an arbitrary moment tensor source is implemented in our forward modeling tool. The increments of shear stress are equally distributed on the staggered grid to implement an accurate and symmetric moment tensor source. Our modeling tool provides an efficient way to obtain the Green’s function in anisotropic media, which is the key of anisotropic moment tensor inversion and source mechanism characterization in microseismic monitoring. In our research, wavefields in anisotropic media have been carefully simulated and analyzed in both surface array and downhole array. The variation characteristics of travel-time and amplitude of direct P- and S-wave in vertical transverse isotropic media and horizontal transverse isotropic media are distinct, thus providing a feasible way to distinguish and identify the anisotropic type of the subsurface. Analyzing the travel-times and amplitudes of the microseismic data is a feasible way to estimate the orientation and density of the induced cracks in hydraulic fracturing. Our anisotropic modeling tool can be used to generate and analyze microseismic full wavefield with full moment tensor source in anisotropic media, which can help promote the anisotropic interpretation and inversion of field data. 相似文献
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全波形反演利用波场的运动学和动力学信息重建地下物理参数,是建立高精度速度模型的有效手段,巨大的计算量是制约其实用化的瓶颈之一。本文针对全波形反演中频率域正演的复杂计算问题,采用粗细结合的并行策略,将MPI技术应用于多炮间并行计算,同时利用GPU技术加速正演过程中大型稀疏线性代数方程组的求解,以提高频率域全波形反演的计算效率。通过理论模型验证本文方法的正确性和有效性,给出不同数据量与GPU计算效率的相关分析结论,提出频率域全波形反演CPU/GPU协同并行计算的制约瓶颈和发展方向。 相似文献
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Surveys in Geophysics - Shales represent strongly intrinsic vertical transverse isotropy (VTI) property or polar anisotropy. The presence of vertically aligned fractures makes shale exhibit... 相似文献
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We examine the one-dimensional direct current method in anisotropic earth formation. We derive an analytic expression of a simple, two-layered anisotropic earth model. Further, we also consider a horizontally layered anisotropic earth response with respect to the digital filter method, which yields a quasi-analytic solution over anisotropic media. These analytic and quasi-analytic solutions are useful tests for numerical codes. A two-dimensional finite difference earth model in anisotropic media is presented in order to generate a synthetic data set for a simple one-dimensional earth. Further, we propose a particle swarm optimization method for estimating the model parameters of a layered anisotropic earth model such as horizontal and vertical resistivities, and thickness. The particle swarm optimization is a naturally inspired meta-heuristic algorithm. The proposed method finds model parameters quite successfully based on synthetic and field data. However, adding 5 % Gaussian noise to the synthetic data increases the ambiguity of the value of the model parameters. For this reason, the results should be controlled by a number of statistical tests. In this study, we use probability density function within 95 % confidence interval, parameter variation of each iteration and frequency distribution of the model parameters to reduce the ambiguity. The result is promising and the proposed method can be used for evaluating one-dimensional direct current data in anisotropic media. 相似文献
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对于非常规油气开发,水力压裂监控的效果取决于对微地震事件的分析、解释.准确的微地震震源位置是关乎施工成败的重要因素.微地震震源位置的准确性与多个参数相关,其不仅依赖于微地震事件的激发时间,同时也依赖于储层介质参数信息,因此进行微地震震源位置、震源时间、储层介质参数的联合反演尤为重要.页岩气储层通常表现出较强的各向异性,... 相似文献
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The optimization inversion method based on derivatives is an important inversion technique in seismic data processing, where
the key problem is how to compute the Jacobian matrix. The computational precision of the Jacobian matrix directly influences
the success of the optimization inversion method. Currently, most of the AVO (amplitude versus offset) inversions are based
on approximate expressions for the Zoeppritz equations to obtain the derivatives of the seismic wave reflection coefficients
(SWRCs) with respect to the stratum parameters. As a result, the computational precision and range of applications of these
AVO inversions are restricted undesirably. In order to improve the computational precision and to extend the range of applications
of AVO inversions, the partial derivative equations of the Zoeppritz equations are established, with respect to the ratios
of wave velocities and medium densities. By solving the partial derivative equations of the Zoeppritz equations accurately,
we obtained the partial derivative of SWRCs with respect to the ratios of seismic wave velocities and medium densities. With
the help of the chain rule for derivatives, the gradient of the SWRCs can be accurately computed. To better understand the
behavior of the gradient of the SWRCs, we plotted the partial derivative curves of the SWRCs, analyzed the characteristics
of these curves, and gained some new insight into the derivatives. Because only a linear system of equations is solved in
our method without adding any new restrictions, the new computational method has both high precision and a quick running speed;
it is not only suitable for small incident angles and weak reflection seismic waves but also for large incident angles and
strong reflection seismic waves. With the theoretical foundations established in the article, we can further study inversion
problems for layered stratum structures and we can further improve the computational speed and precision of the inversions. 相似文献
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Waveform Retrieval and Phase Identification for Seismic Data from the CASS Experiment 总被引:3,自引:0,他引:3
Zhiwei Li Qingyu You Sidao Ni Tianyao Hao Hongti Wang Cantao Zhuang 《Pure and Applied Geophysics》2013,170(5):815-830
The little destruction to the deployment site and high repeatability of the Controlled Accurate Seismic Source (CASS) shows its potential for investigating seismic wave velocities in the Earth's crust. However, the difficulty in retrieving impulsive seismic waveforms from the CASS data and identifying the seismic phases substantially prevents its wide applications. For example, identification of the seismic phases and accurate measurement of travel times are essential for resolving the spatial distribution of seismic velocities in the crust. Until now, it still remains a challenging task to estimate the accurate travel times of different seismic phases from the CASS data which features extended wave trains, unlike processing of the waveforms from impulsive events such as earthquakes or explosive sources. In this study, we introduce a time-frequency analysis method to process the CASS data, and try to retrieve the seismic waveforms and identify the major seismic phases traveling through the crust. We adopt the Wigner-Ville Distribution (WVD) approach which has been used in signal detection and parameter estimation for linear frequency modulation (LFM) signals, and proves to feature the best time-frequency convergence capability. The Wigner-Hough transform (WHT) is applied to retrieve the impulsive waveforms from multi-component LFM signals, which comprise seismic phases with different arrival times. We processed the seismic data of the 40-ton CASS in the field experiment around the Xinfengjiang reservoir with the WVD and WHT methods. The results demonstrate that these methods are effective in waveform retrieval and phase identification, especially for high frequency seismic phases such as PmP and SmS with strong amplitudes in large epicenter distance of 80–120 km. Further studies are still needed to improve the accuracy on travel time estimation, so as to further promote applicability of the CASS for and imaging the seismic velocity structure. 相似文献
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利用区域应力张量阻尼方法,使用南北地震带及其邻近区域2009年1月—2017年8月466次ML≥3.5地震的震源机制解,及1976年1月—2017年8月GCMT公布的259次M≥4.5地震的震源机制解,反演得到研究区1.0°×1.0°网格大小区域的构造应力场。应力场空间分布特征显示,南北地震带作为青藏高原的东边界,由于所处动力环境复杂,其内部最大主应力方向具有明显的空间差异性。这种差异主要表现为:南北地震带北段最大主应力方向为NE向;南北地震带中段及周边除龙门山断裂带NE段最大主应力为NW-NNW向外,其它地段最大主应力近EW向;南北地震带中南段最大主应力方向逐渐由近EW向到NW或NE向,再到近NS向。整体而言,南北地震带及邻近区域最大主应力方向由北到南发生了顺时针旋转。川滇菱形块体内部最大主应力方向为NNW向,应力方向转换带与块体边界基本一致,其东边界以东最大主应力方向为NW向,西边界以西为NNE向。从区域构造应力场的角度分析,难以将“南北地震带”作为一个统一的地震带应用于中长期地震预测的研究与实践中。 相似文献