Anisotropic dual-continuum representations for multiscale poroelastic materials: Development and numerical modelling     

Mark Ashworth  Florian Doster 《国际地质力学数值与分析法杂志》2020,44(17):2304-2328

Dual-continuum (DC) models can be tractable alternatives to explicit approaches for the numerical modelling of multiscale materials with multiphysics behaviours. This work concerns the conceptual and numerical modelling of poroelastically coupled dual-scale materials such as naturally fractured rock. Apart from a few exceptions, previous poroelastic DC models have assumed isotropy of the constituents and the dual-material. Additionally, it is common to assume that only one continuum has intrinsic stiffness properties. Finally, little has been done into validating whether the DC paradigm can capture the global poroelastic behaviours of explicit numerical representations at the DC modelling scale. We address the aforementioned knowledge gaps in two steps. First, we utilise a homogenisation approach based on Levin's theorem to develop a previously derived anisotropic poroelastic constitutive model. Our development incorporates anisotropic intrinsic stiffness properties of both continua. This addition is in analogy to anisotropic fractured rock masses with stiff fractures. Second, we perform numerical modelling to test the DC model against fine-scale explicit equivalents. In doing, we present our hybrid numerical framework, as well as the conditions required for interpretation of the numerical results. The tests themselves progress from materials with isotropic to anisotropic mechanical and flow properties. The fine-scale simulations show that anisotropy can have noticeable effects on deformation and flow behaviour. However, our numerical experiments show that the DC approach can capture the global poroelastic behaviours of both isotropic and anisotropic fine-scale representations.  相似文献   

裂缝、裂隙介质衰减频散研究          下载免费PDF全文

张繁昌  路亚威  桑凯恒  黄建平 《地球物理学报》2019,62(8):3164-3174

为研究裂缝、裂隙介质中波致流引起的衰减,将裂缝看作背景孔隙岩石中非常薄且孔隙度非常高的层状介质,并等价成White周期层状模型.分别考虑不同类型的裂隙和孔隙之间的挤喷流影响,结合改进的Biot方程,推导得到裂缝裂隙介质的刚度与频率的关系.当缝隙中饱含流体时,介质的衰减和速度频散受裂缝、孔隙之间和裂隙、孔隙之间流体流动的显著影响.在低频极限下,裂缝裂隙介质的性质由各向异性Gassmann理论和挤喷流模型获得;而在非常高的频率时,由于缝隙中的压力来不及达到平衡,波致流的影响可忽略.分析表明,裂隙密度主要影响波的衰减,而裂隙纵横比主要控制优势衰减频率和速度显著变化的频率范围;由于不同裂隙的衰减机制不同,衰减和速度频散大小有所差异,但基本趋势相同.  相似文献   

Some remarks on Q-compensated sparse deconvolution without knowing the quality factor Q     

Xintao Chai  Ronghua Peng  Genyang Tang  Wei Chen  Jingnan Li 《Geophysical Prospecting》2019,67(8):2003-2021

The subsurface media are not perfectly elastic, thus anelastic absorption, attenuation and dispersion (aka Q filtering) effects occur during wave propagation, diminishing seismic resolution. Compensating for anelastic effects is imperative for resolution enhancement. Q values are required for most of conventional Q-compensation methods, and the source wavelet is additionally required for some of them. Based on the previous work of non-stationary sparse reflectivity inversion, we evaluate a series of methods for Q-compensation with/without knowing Q and with/without knowing wavelet. We demonstrate that if Q-compensation takes the wavelet into account, it generates better results for the severely attenuated components, benefiting from the sparsity promotion. We then evaluate a two-phase Q-compensation method in the frequency domain to eliminate Q requirement. In phase 1, the observed seismogram is disintegrated into the least number of Q-filtered wavelets chosen from a dictionary by optimizing a basis pursuit denoising problem, where the dictionary is composed of the known wavelet with different propagation times, each filtered with a range of possible values. The elements of the dictionary are weighted by the infinity norm of the corresponding column and further preconditioned to provide wavelets of different values and different propagation times equal probability to entry into the solution space. In phase 2, we derive analytic solutions for estimates of reflectivity and Q and solve an over-determined equation to obtain the final reflectivity series and Q values, where both the amplitude and phase information are utilized to estimate the Q values. The evaluated inversion-based Q estimation method handles the wave-interference effects better than conventional spectral-ratio-based methods. For Q-compensation, we investigate why sparsity promoting does matter. Numerical and field data experiments indicate the feasibility of the evaluated method of Q-compensation without knowing Q but with wavelet given.  相似文献   

剪切波分裂揭示的青藏高原上地壳地震各向异性基本特征          下载免费PDF全文

郭铁龙  高原 《地球物理学报》2020,63(3):1085-1103

青藏高原整体隆升,构造运动与介质变形强烈,然而由于地震观测数据不足,青藏高原内部上地壳各向异性研究一直是一个空白.本研究使用西藏地区的地震台网(2009年5月—2017年5月)的观测资料,利用剪切波分裂研究青藏高原上地壳地震各向异性特征.由于青藏高原固定地震台站分布稀疏,可用于进行剪切波分裂研究的近场地震事件记录稀少,本研究采用地震事件的单台定位技术,对公开的地震目录里没有震源深度数据的地震事件进行震源位置约束,并引入微震模板匹配定位方法,对连续地震波形进行检索,识别出地震目录里遗漏的新的微震(小地震)事件波形.微震识别获得的新地震事件记录是地震目录里报告的地震事件记录的大约6倍,用于补充研究区的剪切波分裂数据分析.通过数据分析,对比快波偏振方向,证实微震识别获得的数据极大地增加了有效数据的数量,提高了结果的可靠性.研究结果表明,雅鲁藏布江缝合带与班公—怒江缝合带之间的拉萨地块东部地区,台站的快剪切波(快波)偏振方向主要受区域应力场影响,快波偏振方向主要是NS或NNE方向,表明了区域最大主压应力方向;但个别地震台站(当雄台)快波偏振方向受原地主压应力影响,其快波偏振方向既不平行于断裂走向也不平行于区域主压应力方向,揭示出地壳介质的局部变形导致的局部应力方向不同于青藏块体里的其他地区.研究区西部的改则、普兰和研究区北部的双湖,快波偏振方向显示与断裂等构造走向一致的特点.研究区东部的昌都和察隅,快波偏振方向除了与断裂走向(或构造线)一致,还与地表运动的方向相同,揭示了青藏块体东部的深部物质可能的运移方向.这个现象虽然还需更多的研究证实,但这个发现的重要启示是,地震各向异性结合地表变形可用于探讨地壳深部物质的运动.  相似文献   

Modelling of viscoacoustic wave propagation in transversely isotropic media using decoupled fractional Laplacians     

Zhihao Qiao  Chengyu Sun  Jie Tang 《Geophysical Prospecting》2020,68(8):2400-2418

A new wave equation is derived for modelling viscoacoustic wave propagation in transversely isotropic media under acoustic transverse isotropy approximation. The formulas expressed by fractional Laplacian operators can well model the constant-Q (i.e. frequency-independent quality factor) attenuation, anisotropic attenuation, decoupled amplitude loss and velocity dispersion behaviours. The proposed viscoacoustic anisotropic equation can keep consistent velocity and attenuation anisotropy effects with that of qP-wave in the constant-Q viscoelastic anisotropic theory. For numerical simulations, the staggered-grid pseudo-spectral method is implemented to solve the velocity–stress formulation of wave equation in the time domain. The constant fractional-order Laplacian approximation method is used to cope with spatial variable-order fractional Laplacians for efficient modelling in heterogeneous velocity and Q media. Simulation results for a homogeneous model show the decoupling of velocity dispersion and amplitude loss effects of the constant-Q equation, and illustrate the influence of anisotropic attenuation on seismic wavefields. The modelling example of a layered model illustrates the accuracy of the constant fractional-order Laplacian approximation method. Finally, the Hess vertical transversely isotropic model is used to validate the applicability of the formulation and algorithm for heterogeneous media.  相似文献   

A simple hypoplastic model with loading surface accounting for viscous and fabric effects of clays     

Merita Tafili  Theodoros Triantafyllidis 《国际地质力学数值与分析法杂志》2020,44(16):2189-2215

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A plasticity constitutive model for unsaturated,anisotropic, nonexpansive soils     

Panagiotis Sitarenios  Michael Kavvadas 《国际地质力学数值与分析法杂志》2020,44(4):435-454

The paper describes and evaluates an incremental plasticity constitutive model for unsaturated, anisotropic, nonexpansive soils (CMUA). It is based on the modified Cam-Clay (MCC) model for saturated soils and enhances it by introducing anisotropy (via rotation of the MCC yield surface) and an unsaturated compressibility framework describing a double dependence of compressibility on suction and on the degree of saturation of macroporosity. As the anisotropic and unsaturated features can be activated independently, the model is downwards compatible with the MCC model. The CMUA model can simulate effectively: the dependence of compressibility on the level of developed anisotropy, uniqueness of critical state independent of the initial anisotropy, an evolving compressibility during constant suction compression, and a maximum of collapse. The model uses Bishop's average skeleton stress as its first constitutive variable, favouring its numerical implementation in commercial numerical analysis codes (eg, finite element codes) and a unified treatment of saturated and unsaturated material states.  相似文献   

2018年2月12日河北永清4.3级地震强震动记录分析     

郭秋娜  温超  周月玲  李姜 《震灾防御技术》2020,15(2):329-338

2018年2月12日河北省廊坊市永清县发生4.3级地震，震中位于廊固凹陷内的河西务断裂附近，国家强震动台网中心获取74组强震动记录，本文对触发台站进行场地分类，结果显示大部分为Ⅰ类场地(51.35%)，其次为Ⅱ类场地(35.14%)和Ⅲ类场地(13.51%)。根据5个典型台站加速度时程记录及反应谱分析本次地震强震动特征，并对各台站峰值加速度反应谱与方位角和震中距的关系进行分析。采用克里格插值方法绘制地震仪器烈度分布图，由于台站分布不均，导致极震区附近烈度影响场计算缺值现象，本文通过拟合本次地震强震动记录得到该地区地震动衰减关系，在空白区域建立空间随机假设台站进行补点插值，解决了计算缺值问题，为缺少台站记录的震区提供准确快速制作烈度分布图的思路，为震害调查和地震应急救援提供重要依据。  相似文献   

乌海地区剪切波分裂研究     

魏建民  张晖  赵星  张浩鸣  郝亮  阿那尔 《震灾防御技术》2020,15(4):777-787

根据乌海地区构造环境，采用SAM方法研究乌海地区地壳各向异性特征，使用乌海地震台2014年1月至2020年6月数字地震波形进行分析。根据65个有效地震记录，得到乌海地区剪切波分裂参数，其中快剪切波平均优势偏振方向为NE63.1°±46.4°，慢剪切波平均时间延迟为（1.13±0.66）ms/km。乌海地震台快剪切波偏振显示出4个优势偏振方向，分别为NE、EW、NNE、NNW向。将得到的各向异性结果与研究区应力场和地质构造进行分析，认为研究区周边复杂的剪切波分裂变化是主压应力场、原地主压应力、断裂带分布共同作用的结果。  相似文献   

利用远震研究四川盆地及其周缘瑞利面波相速度和方位各向异性          下载免费PDF全文

王小龙  雷兴林  马胜利  张烨  郭志  闻学泽 《地球物理学报》2020,63(2):445-459

基于四川盆地及周边的245个宽频带台站2010年9月—2014年9月期间的远震记录,提取双台路径瑞利面波相速度频散资料,反演得到四川盆地20～120s的高分辨率瑞利面波相速度及各向异性空间分布.在丰富区域地球物理基础数据的同时,结合已有研究成果对地壳上地幔变形耦合进行探讨,结果表明短周期(20～30s)的相速度分布与四川盆地的地质构造特征相吻合,作为川滇地块、松潘—甘孜地块和四川盆地之间的边界——龙门山断裂带和鲜水河断裂带对上述三个地块上地壳的速度结构具有明显的控制作用;松潘—甘孜地块,特别是川滇地块中下地壳普遍表现为明显的低速异常,表明中下地壳相对软弱;而四川盆地的中下地壳整体呈现相对高速,表明四川盆地具有相对坚硬的中下地壳.研究区域东南角接近北扬子地块与南扬子地块的缝合部位,呈现高速异常.四川盆地南部和东南邻区不同周期均具有较强的各向异性,且快波方向较为一致,反映这些地区不同深度变形耦合较好.四川盆地西部、北部及东北部邻区,不同周期的各向异性快波方向变化较大,不同深度变形耦合较差.这些特征与绕喜马拉雅东构造结的物质流动被扬子地块的高速地壳阻挡的宏观认识基本一致.  相似文献