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1.
《地震研究进展（英文）》2021,1(1):100005
Seismic anisotropy is an effective feature to study the inner structure of the Earth. In complex tectonic area, the assumption of single-layer anisotropy is sometimes not well consistent with the observed data; thus, the assumption of multi-layered (i.e. stratified) anisotropy should be considered. At present, the main methods to study anisotropy include receiver functions, shear wave splitting from local and teleseismic events (SKS, SKKS, and PKS, hereafter collectively called XKS), P- and Pn wave travel time inversion, surface wave inversion from far-field earthquakes and ambient noise. Each of the above method has its own advantages and limitations. Thus, one or more of the above methods are often combined to characterize multi-layered anisotropy, of which the depth range of anisotropic layers are different. This paper reviews the research progress of multi-layered anisotropy for the purpose of providing a basis for future seismic anisotropy investigations. 相似文献
2.
《中国地震研究》2021,(1)
Seismic anisotropy is an effective feature to study the inner structure of the Earth. In complex tectonic area, the assumption of single-layer anisotropy is sometimes not well consistent with the observed data; thus, the assumption of multi-layered(i.e. stratified) anisotropy should be considered. At present, the main methods to study anisotropy include receiver functions, shear wave splitting from local and teleseismic events(SKS, SKKS,and PKS, hereafter collectively called XKS), P-and Pn wave travel time inversion, surface wave inversion from farfield earthquakes and ambient noise. Each of the above method has its own advantages and limitations. Thus, one or more of the above methods are often combined to characterize multi-layered anisotropy, of which the depth range of anisotropic layers are different. This paper reviews the research progress of multi-layered anisotropy for the purpose of providing a basis for future seismic anisotropy investigations. 相似文献
3.
CRYSTALLOGRAPHIC PREFERRED ORIENTATION(CPO) OF ANISOTROPIC MINERALS IN THE LITHOSPHERE AND ITS SIGNIFICANCE TO THE STUDY OFLITHOSPHERE DYNAMICS 
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下载免费PDF全文 Seismic anisotropy has been widely used to constrain deformation and mantle flow within the upper mantle of the Earth's interior, and is mainly affected by crystallographic preferred orientation(CPO)of anisotropic mineral in lithosphere. Anisotropy of peridotites caused by deformation is the main source of seismic anisotropy in the upper mantle. Olivine is the most abundant and easily deformed mineral to form CPO in peridotite, thus the CPO of olivine controls seismic anisotropy in the upper mantle. Based on simple shear experiments and studies of natural peridotites deformation, several CPO types of olivine have been identified, including A, B, C, D, E and AG-type. Studies on the deformation of olivine have shown that the CPO of olivine is mainly related to stress, water content, temperature, pressure, partial melting and melt/fluid percolation. Most of the seismic anisotropy has been explained by the A-type olivine CPO in the upper mantle, which is commonly found in upper-mantle peridotites and produced by the simple shear in dry conditions. Previous studies showed that anisotropy was attributed to the CPO of mica and amphibole in the middle-lower crust. The comparison between mantle anisotropy calculated from mineral CPO and regional anisotropy deduced from geophysical methods is therefore particularly useful for interpreting the deformation mechanisms and geodynamic processes which affect the upper mantle in different tectonic units such as subduction system, continental rift and continental collision zone in the world. The paper summarizes the characteristics of CPO and anisotropy of major anisotropic minerals in the upper mantle. Taking the lithosphere mantle xenoliths in the southeastern Tibetan plateau as an example, we perform detailed studies on the microstructures and seismic anisotropy to better understand the deformation mechanisms and upper mantle anisotropy in this region. Results show that the CPO of olivine in peridotite xenoliths in southeastern Tibetan plateau are A-type and AG-type. The mechanisms proposed for the formation of AG-type are different from that for the A-type. Therefore, the occurrence of AG-type olivine CPO pattern suggests that this CPO may record a change in deformation mechanism and tectonic environment of the lithosphere in southeastern Tibetan plateau. Provided that the strong SKS(shear wave splitting)observed in southeastern Tibetan plateau results from lithosphere mantle, the lithosphere mantle in this region is expected to be at least 130km thick and characterized by vertical foliation. Considering that the thickness of lithosphere in southeastern Tibetan plateau is much less than 130km and the lithosphere mantle cannot explain the anisotropy measured by SKS, other anisotropy sources should be considered, such as anisotropy in the asthenosphere and the oriented melt pockets(MPO)in the upper mantle. Therefore, detailed study of CPO of anisotropic mineral is essential for constraining geophysical measurements and analyzing the dynamic process of the lithosphere reasonably. 相似文献
4.
Seismic anisotropy is a relatively common seismic wave phenomenon in laminated sedimentary rocks such as shale and it can be used to investigate mechanical properties of such rocks and other geological materials. Young’s modulus and Poisson’s ratio are the most common mechanical properties determined in various rock engineering practices. Approximate and explicit equations are proposed for determining Young’s modulus and Poisson’s ratio in anisotropic rocks, in which the symmetry plane and symmetry axis of the anisotropy are derived from the constitutive equation of transversely isotropic rock. These equations are based on the media decomposition principle and seismic wave perturbation theory and their accuracy is tested on two sets of laboratory data. A strong correlation is found for Young’s modulus in two principal directions and for Poisson’s ratio along the symmetry plane. Further, there is an underprediction of Poisson’s ratio along the symmetry axis, although the overall behavior follows the trend of the measured data. Tests on a real dataset show that it is necessary to account for anisotropy when characterizing rock mechanical properties of shale. The approximate equations can effectively estimate anisotropic Young’s modulus and Poisson’s ratio, both of which are critical rock mechanical data input for hydraulic fracturing engineering. 相似文献
5.
The geometry of faults at seismogenic depths and their continuation into the ductile zone is of interest for a number of applications ranging from earthquake hazard to modes of lithospheric deformation. Teleseismic passive source imaging of faults and shear zones can be useful particularly where faults are not outlined by local seismicity. Passive seismic signatures of faults may arise from abrupt changes in lithology or foliation orientation in the upper crust, and from mylonitic shear zones at greater depths. Faults and shear zones with less than near-vertical dip lend themselves to detection with teleseismic mode-converted waves (receiver functions) provided that they have either a contrast in isotropic shear velocity (V s), or a contrast in orientation or strength of anisotropic compressional velocity (V p). We introduce a detection method for faults and shear zones based on receiver functions. We use synthetic seismograms to demonstrate common features of dipping isotropic interfaces and contrasts in dipping foliation that allows determination of their strike and depth without making further assumptions about the model. We proceed with two applications. We first image a Laramide thrust fault in the western U.S. (the Wind River thrust fault) as a steeply dipping isotropic velocity contrast in the middle crust near the surface trace of the fault; further downdip and across the range, where basin geometry suggests the fault may sole into a subhorizontal shear zone, we identify a candidate shear zone signal from midcrustal depths. The second application is the use of microstructural data from exhumed ductile shear zones in Scotland and in the western Canadian Shield to predict the character of seismic signatures of present-day deep crustal shear zones. Realistic anisotropy in observed shear fabrics generates a signal in receiver functions that is comparable in amplitude to first-order features like the Moho. Observables that can be robustly constrained without significant tradeoffs are foliation strike and the depth of the foliation contrast. We find that an anisotropy of only a few percent in the shear zone is sufficient to generate a strong signal, but that the shear zone width is required to be >2 km for typical frequencies used in receiver function analysis to avoid destructive interference due to the signals from the boundaries of the shear zone. 相似文献
6.
Seismic anisotropy of a fractured karstic limestone massif in sub-parallel underground galleries is studied. As the fractures are mostly vertically oriented, the seismic properties of the massif are approximated by horizontal transverse isotropy (HTI). Several data inversion methods were applied to a seismic dataset of arrival-times of P and S-waves.The applied methods include: isotropic tomography, simple cosine function fit, homogeneous Monte-Carlo anisotropic inversion for the parameters of horizontal transverse isotropy and anisotropic tomography for tilted transversely isotropic bodies. All methods lead to the conclusion that there is indeed an anisotropy present in the rock massif and confirm the direction of maximum velocity parallel to the direction of fracturing. Strong anisotropy of about 15% is found in the studied area. Repeated measurements show variations of the P-wave parameters, but not of the S-wave parameters, which is reflecting a change in water saturation. 相似文献
7.
利用蒙古中南部地区布设的69套宽频带数字地震仪2011年8月—2013年7月记录的远震事件,使用时间域反褶积方法提取接收函数,并挑选高质量Pms震相,通过改进的剪切波分裂方法对研究区地壳各向异性参数进行了研究,最终获取了1473对各向异性参数.经过统计分析,有48个台站可以归纳出两个方向的各向异性,11台站得到单个方向的各向异性,而剩余10个台站各向异性方向比较发散.结果显示,各向异性在蒙古中南部地壳中呈不均匀分布,有54个台站得到了NE-SW向各向异性,快波偏振方向平均值为N58°E±16°,与最大水平主应力σHmax方向和区域内主要断层走向一致,说明这部分地壳各向异性的主要成因存在于上地壳,可能与流体填充的微裂隙有关.而NW-SE向各向异性在53个台站被观测到,各向异性方向变化范围平均N132°E±16°,与研究区大部分SKS分裂快波方向具有较好的一致性,说明下地壳成岩矿物晶体定向排列是各向异性的主要成因.研究区地壳各向异性的分层特征总体上支持岩石圈受到NE-SW向挤压的动力学模型. 相似文献
8.
在各向异性地壳中,来自Moho的P-to-S转换波(Pms)的到时不仅取决于入射角和地壳厚度,而且还随地震事件方位角而变化.地处青藏高原东南缘的川滇地区,地壳变形十分强烈.本文利用川滇地区的108个固定台站记录的远震三分量地震波形数据提取台站下方的P波接收函数,并把接收函数被校正到了同一参考震中距处(例如67°).然后按后方位角10°为间隔将接收函数叠加成一道信号以增强信噪比,并从叠加信号里拾取不同后方位角对应的Pms相的观测到时.在快波极化方向和分裂时间构成的解的平面上,能使观测到时与理论到时之差最小的点即为所求的分裂参数的位置.合成地震图和实际观测数据的实验表明,这个方法不但稳定性较好,而且误差估计也较小.我们从108个台中获得了96个Pms相的分裂参数,结果表明,川滇地区地壳各向异性十分强烈,Pms相分裂时间在0.05s±0.06s到1.27s±0.10s之间,平均值为0.54s±0.12s.地壳各向异性的快波极化方向与地表GPS速度场的差异性表明,印支块体的上下地壳之间是解耦的,而川滇菱形块体北部、松藩—甘孜和四川盆地的上下地壳之间是耦合的.然而,川滇菱形块体南部,地壳变形主要受控于小江断裂和金沙江—红河断裂. 相似文献
9.
M. Pohl. F. Wenzel T. Weiss S. Siegesmund T. Bohlen W. Rabbel 《Pure and Applied Geophysics》1999,156(1-2):139-155
—The genesis of the laminated lower crust has been attributed to extensional processes leading to structural and textural ordering. This implies that the lower crust might be anisotropic. Laboratory measurements of lower crustal rock samples and xenolithes show evidence of anisotropy in these rocks due to oriented structure.¶In this paper we investigate the seismic shear-wave response of realistic anisotropic lower crustal models using the anisotropic reflectivity method. Our models are based on representative petrophysical data obtained from exposed lower crustal sections in Calabria (South Italy), Val Strona and Val Sesia (Ivrea Zone, Northern Italy). The models consist of stacks of anisotropic layers characterized by quantified elastic tensors derived from representative rock samples which provide alternating high and low velocity layers.¶The seismic signature of the data is comparable to seismic observations of in situ lower crust. For the models based on the Calabria and Val Strona sequences shear-wave splitting occurs for the Moho reflection at offsets beyond 70 km with travel-time delays up to 300 and 500 ms, respectively. The leading shear wave is predominantly horizontally polarized and followed by a predominantly vertically polarized shear wave. Contrastingly, the Val Sesia model shows no clear evidence of birefringence. Isotropic versus anisotropic modelling demonstrates that the shear-wave splitting is clearly related to the intrinsic anisotropy of the lower crustal rocks for the Val Strona sequence. No evidence of birefringence caused by thin layering is found. 相似文献
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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
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岩石圈各向异性主要由上地幔矿物晶格优势排列方向和上地壳内裂缝、裂隙的定向分布造成.在各向异性特征显著区域,利用SKS震相剪切波分裂获得的延迟时间高达1.5s以上.本文根据方位各向异性,利用广义反射透射系数矩阵方法正演S波接收函数,研究各向异性对不同反方位角接收函数转换震相走时的影响.我们发展了基于HTI模型各向异性走时校正的方法,成功的在单层和多层(快轴方向相同或不同)的各向异性介质中对齐不同反方位角接收函数的Moho面和LAB的转换震相走时.我们将该方法应用于在青藏高原东北缘的流动台站,试图在各向异性强度较大区域对实测数据转换震相走时的校正效果进行测试.结果表明:各向异性走时校正能够加强单台接收函数转换震相的可追踪性,能量增强的叠后转换震相在时深转换后更利于对界面深度的识别与判断;在考虑三维成像的情况下,我们的各向异性校正方法对提高成像结果的准确性有重要意义. 相似文献
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Receiver function imaging in strongly laterally heterogeneous crust: Synthetic modeling of BOLIVAR data 下载免费PDF全文
下载免费PDF全文 We resolve a large (~20 km) discrepancy in Moho depth determined from PdS receiver functions (RFs) and from active source seismic profiling in the complex Caribbean-South American plate boundary zone in eastern Venezuela. As part of the BOLIVAR experiment 20 broadband stations were deployed along an active source profile to record teleseisms. Using the extremely heterogeneous crustal model obtained from active source data, we generated 2D finite-difference elastic wave synthetics and from them calculated receiver functions and CCP stacks. We compare the observations with synthetic sections that have been spatially sampled at 0.25 km to 40 km. The densely sampled synthetics show that several events in the field data that were originally interpreted as the Moho are multiple reflections within sedimentary basins. Where the Moho has the steepest dip under the plate boundary the CCP stacks fail to image the Moho well, regardless of the density of spatial sampling. A suitable spatial sampling criterion for clearly imaging the lower crust and Moho is to overlap Fresnel zones by 50% at Moho depth, which for the 1 Hz receiver functions examined here, requires an instrument spacing of 15–20 km, with the actual field data density ranging from 20 km to 100 km. 相似文献
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Natural gas origins of large and medium-scale gas fields in China sedimentary basins 总被引：2，自引：0，他引：2
The integrated study of the geological and seismic reflection data from the drilling area of CCSD has discovered that the density and the P-wave velocity of orthogneiss are almost the same as that of the paragneiss in the area; but the orthogneiss and the paragneiss hold different reflection attributes. The strong seismic reflector packes coinciding spatially with the paragneiss suites have implied that the paragneiss buried in the metamorphic crust itself can cause bone-like seismic reflector sets. The P-wave velocity of paragneiss shows little apparent difference with that of the orthogneiss; but its transverse wave velocity is lower, with the Vp/Vs ratios being high. The paragneiss has partially inherited the layering structures and textures of the protolithe of sedimentary rocks, hence shows strong heterogeneity and anisotropy, that is why the paragneiss are able to produce the bone-like reflectors in the upper crust. The low transverse wave velocity of paragneiss often means weak shear resistance, which will further cause cracks or fractures in the rock, consequentially increase its porosity and permeability during tectonic movements, and form the paragneiss reservoirs of low-permeability zones for gases uplifted from the deeper crust. Because the paragneiss in the crustal metamorphic basement can cause the seismic reflectors, seismic reflection sections are able to provide information about the paragneiss under certain prerequisites. 相似文献
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地壳不同深度介质的地震各向异性是研究地壳不同深度范围变形方式的重要依据.鉴于地壳介质的复杂性,如何从远震体波接收函数中提取不同深度的各向异性参数仍是一个有待深入研究的课题.在已有研究的基础上,本文利用广义反射-透射系数矩阵方法计算的合成地震图,研究了复杂地壳分层各向异性介质的接收函数随反方位角(back azimuth)变化及不同层位各向异性参数对接收函数波场的影响,为各向异性介质接收函数的解释提供了新的理论依据.通过引入粒子群优化理论,发展了分层各向异性介质接收函数全局反演算法.数值及观测数据的验证结果表明,在各向同性速度模型确定的前提下,我们的方法能够可靠地提取地壳分层各向异性参数;在反演中引入曲波变换去噪技术,对于正确解析不同层位的各向异性参数具有重要价值. 相似文献
16.
选取重庆地震台2010年至2012年记录的60个远震宽频带数字地震记录,采用频率域反褶积法获得台站的接收函数,采用H-Kappa叠加方法反演台站下方的地壳厚度和泊松比,作为台站下方波速反演的约束条件,以减少反演的非唯一性.计算结果显示,重庆地震台下方地壳厚度为42 km,与中国大陆中西部地区Moho面深度在38-45 km保持一致.该研究对增强该区的深部地质构造特征、分析孕震机制等具有积极意义. 相似文献
17.
本文通过对出露于青藏高原东南缘云南六合地区的新生代深源岩石包体(斜长角闪岩、角闪石岩和石榴石透辉岩)的显微组构和地震波各向异性的研究来约束新生代青藏高原东南缘的地壳各向异性.通过角闪石地质压力计计算得知斜长角闪岩、角闪石岩和石榴石透辉岩包体来源于地壳28～36km,为中-下地壳岩石包体.EBSD测量结果显示包体中角闪石的CPO (晶格优选定向)为Type-IV型和(100)[001]滑移,单斜辉石的CPO为SL型和(100)[001]滑移,暗示中-下地壳为高温强变形的特征.通过CPO数据计算获得斜长角闪岩、角闪石岩和石榴石透辉岩包体全岩VP各向异性为1.9%～13.3%,最大分裂的剪切波各向异性(AVS)为1.17%～8.01%.结合前人的研究结果,该地区的地壳岩石能够解释利用Pms震相测量获得的分裂延迟时间,表明云南西北地区的壳内各向异性源于中-下地壳矿物的定向排列.云南西北地区的Pms快波方向近NW-SE向分布并与SKS的快波方向相近,暗示岩石圈变形是耦合的,受控于青藏高原向东南挤出的构造背景. 相似文献
18.
Jean-Paul Montagner 《Pure and Applied Geophysics》1998,151(2-4):223-256
—During the last 30 years, considerable evidence of seismic anisotropy has accumulated demonstrating that it is present at all scales, but not in all depth ranges. We detail which conditions are necessary to detect large-scale seismic anisotropy. Firstly, minerals must display a strong anisotropy at the microscopic scale, and/or the medium must be finely layered. Secondly, the relative orientations of symmetry axes in the different crystals must not counteract in destroying the intrinsic anisotropy of each mineral, and there must be efficient mechanisms of orientation of minerals and aggregates. Finally, the strain field must be coherent at large scale in order to preserve long wavelength anisotropy. Part of shallow anisotropy can be related to the past strain field (frozen-in anisotropy), however the deep anisotropy is due to the present strain field. All these conditions are fulfilled only in boundary layers of convective mantle.¶We review in this paper, the seismic data sets which provide insight into the location at depth of large-scale anisotropy from the D"-layer up to the lithosphere. In addition to the well-documented seismic anisotropy in the lithosphere and asthenosphere, there is new evidence of seismic anisotropy in the upper (400–660 km) and lower (660–900 km) transition zones and in the D"-layer. Nonetheless the bulk of the lower mantle seems close to isotropy. If we assume the hypothesis that seismic anisotropy is associated with boundary layers in convective systems, these observations strongly suggest that the transition zone is a boundary layer which makes the pasage of matter between the upper and the lower mantle difficult. However, this general statement does not rule out flow circulation between the upper and lower mantles. Finally, the geophysical, mineral physics and geological applications are briefly reviewed. An intercomparison between surface wave anisotropy and body-wave anisotropy data sets is presented. We discuss the scientific potential of seismic anisotropy and how it makes it possible to gain more insight into continental root, deformation and geodynamics processes. 相似文献
19.
This study attempts to determine the relation between source parameters and mechanical properties of the rock matrix in which the microseismic events occur. For this purpose, accurate geological, mechanical and seismological data were acquired on a gas field experiencing induced seismicity due to its reservoir pressure drop. More than 30 deep boreholes (depth greater than 4 km) are concentrated in a 10×10×5 km volume, providing core samples for both geological and mechanical assessment. In this study, we focus on induced seismic events recorded by the local seismic network, over a three-year-long period. Characteristics of the seismic sources were obtained using spectral analysis and a dynamic model of failure. Results point out correlation between physical parameters of the seismic sources and the geomechanical properties of the rocks involved. Maximal static stress drops are found to be associated with the mechanical strength of the geological strata where the rupture occurs. The fracture size, using a circular model of failure, is also found to be dependent on the geomechanical setting. It is found that the size of the seismic fractures is dependent on the layer thickness and the prefracturation of the medium, both factors influencing the extension of preexisting discontinuities. The parameters of the seismic sources also show important changes when the gas reservoir is reached. The reservoir unit experienced a 45 MPa pore fluid pressure drop over a period of 20 years. 相似文献
20.
Estimating azimuthal stress‐induced P‐wave anisotropy from S‐wave anisotropy using sonic log or vertical seismic profile data 下载免费PDF全文
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