共查询到20条相似文献，搜索用时 593 毫秒
1.
The anisotropic modelling of intensity distribution, affected by the construction of macroseismic planes, allows an analysis of the influence of each point of observed intensity on the analytical determination of epicenter and of the principal attenuation directions. Such a procedure is a vital aid in the cases in which the observed intensity points, that, for location or joined intensity level, are not consistent with an anisotropic model of intensity attenuation. A suitable filtering on intensity levels associated with the points of the intensity map, for a better modelling of observed intensity distribution, is proposed with the aim of a better seismic hazard evaluation. 相似文献
2.
A procedure is proposed for the reconfiguration of the macroseismic planes relative to earthquakes that, being characterized by a reduced number of points of observed intensity due to a lack of information, or having the epicenter very close to the coastline, are characterized by an incomplete distribution of observed intensity levels. The design of a plurality of virtual areas, through which a distribution of intensity consistent with an anisotropic model of attenuation is depicted, allows a reliable determination of macroseismic parameters of the same seismic event. 相似文献
3.
Fiona Simpson 《Earth and Planetary Science Letters》2002,203(1):535-547
It has been hypothesised that seismic and electrical anisotropy at the base of the lithosphere are caused by strain-induced lattice-preferred orientation (LPO) of olivine [100] axes parallel to present-day plate motion. This would imply that seismic and electrical anisotropy observations can provide geodynamicists with fundamental information for characterising mantle flow. The qualitative agreement between the fast direction of SV-waves and direction of maximum electrical conductance modelled deeper than 150 km below the North Central craton of Australia appear to support a common alignment mechanism, and the observed, anisotropic electrical conductances can be generated by hydrogen diffusivity in a water-poor (<1000 ppm H/Si) olivine mantle. A quantitative test is proposed for the hypothesis that electrical anisotropy is generated by anisotropic hydrogen diffusion rates (D) in olivine. Electrical anisotropy factors are computed using random resistor network models assuming that D[100]≈20×D[010]≈40×D[001]. Electrical and seismic anisotropies calculated from olivine LPO angular distribution functions modelled for a range of shear strains under a simple shear deformation demonstrate that the intensity of olivine [100] alignments (and associated shear strains) that would be required to explain the electrical anisotropy in the mantle below central Australia are significantly greater than predicted by Rayleigh wave anisotropies. The poor agreement between the observed electrical anisotropies and the electrical anisotropies that would be predicted from the Rayleigh wave anisotropies indicates that either (i) electrical anisotropy in the upper mantle below central Australia is not generated by hydrogen diffusivity alone or (ii) the seismic anisotropy is underestimated. The orientation of the olivine [100] axes maxima is inferred to be ∼30° rotated relative to the direction of present-day absolute plate motion (APM) that is determined relative to the hotspot reference frame (HS2-NUVEL1). Both the APM direction that is determined relative to a reference frame defined by requiring no-net rotation of the lithosphere (NNR-NUVEL1) and GPS-derived plate motion vectors fit the geophysical observations of upper mantle anisotropy better. This may support the contention that hotspots are not stationary relative to the deep mantle. 相似文献
4.
5.
6.
可控源音频大地电磁测深法(CSAMT)基本上是基于电性各向同性理论的假设,而实际地层普遍表现为电性各向异性现象,因此研究各向异性地层条件下CSAMT方法的电磁响应具有重要的理论意义和应用价值.本文从有源Maxwell方程出发,推导出了二维各向异性地层条件下无限长线源频率域的电磁场响应,得到了一组平行于线源方向的电场分量E_x和磁场分量H_x的偏微分方程,并采用有限元法进行求解.模型的计算结果表明:不论是对均匀半空间还是一维层状介质中的各向异性二维体模型的计算,均能从结果中明显地看出各向同性背景场和各向异性异常体的存在;在计算中通过改变各向异性系数或各向异性旋转角,其结果在视电阻率和相位曲线上均存在显著区别.计算结果表明了在各向异性地层中,仍然采用各向同性的假设进行CSAMT资料的处理与解释,可能会带来比较严重的误差,这种情况下必须采用基于各向异性的地质模型对CSAMT资料进行处理和解释.研究结果对于提高CSAMT方法的勘探效果和应用水平具有重要的指导意义. 相似文献
7.
在长波长假设条件下,水平层状地层中发育一组垂直排列的裂缝构成了等效正交各向异性介质.各向异性参数与裂缝弱度参数的估算有助于非均匀各向异性介质的各向异性特征描述,而弹性逆散射理论是非均匀介质参数反演的有效途径.基于地震散射理论,我们首先推导了非均匀正交介质中纵波散射系数方程,并通过引入正交各向异性特征参数,提出了一种新颖的正交各向异性方位弹性阻抗参数化方法.为了提高反演的稳定性与横向连续性,我们发展了贝叶斯框架下的正交各向异性方位弹性阻抗反演方法,同时考虑了柯西稀疏约束正则化和平滑模型约束正则化,最终使用非线性的迭代重加权最小二乘策略实现了各向异性特征参数的稳定估算.模型和实际资料处理表明,反演结果与测井解释数据相吻合,证明了该方法能够稳定可靠地从方位叠前地震资料中获取各向异性特征参数,减小参数估算的不确定性,为非均匀正交介质的各向异性预测提供了一种高可靠性的地震反演方法. 相似文献
8.
The spatial distributions of the intensity and polarization of hard X-rays (HXR) were modeled based on a numerical solution of the nonstationary kinetic Fokker-Plank equation. Two cases of nonstationary long injections (??10 s) of nonthermal electrons at the top of a flaring loop are considered. In the first case, the injection occurs anisotropically in a cone directed along the field to one of the loop??s footpoints. In the second case, electrons are injected isotropically. In the case of the anisotropic injection, the degree of HXR polarization in the footpoints is low and does not exceed 8%. At the same time, the polarization of the radiation from the top in a range of photon energies from 30 to 60 keV reaches 43% at the beginning of injection. Significantly different spatial distributions of HXR characteristics are obtained for the isotropic injection of electrons. In this case, the calculated degree of HXR polarization from the top exhibits a strong variability: it reaches 15?C18% at the beginning of injection at photon energies of 30?C90 keV, decreases to zero after 5 s, and then, changing its sign, increases to 8%. In the footpoint of the loop, HXR is in fact nonpolarized. The features of the spatial distributions obtained in the simulation process can be measured with X-ray telescopes-polarimeters in future experiments and used for diagnosing the pitch angle distribution of accelerated electrons. 相似文献
9.
煤层中存在的裂隙会导致介质表现为各向异性,本文以HTI型煤层为例,结合各向异性介质弹性矩阵和各向异性裂隙理论,推导出不同充填物的垂直裂隙中各向异性参数表达式,将其应用于地震波响应分析;通过改进的交错网格差分法和各向异性Christoffel方程波场分解法,得到地震波合成记录和分解后的P波和SV波记录;将Thomsen群速度与相速度公式,经过坐标轴旋转变换,得到HTI型煤层中不同各向异性参数的地震波速度响应表达式;建立不同类型煤层地质模型,分析了裂隙密度、裂隙充填物以及煤层厚度等参数变化时的地震波响应特征.研究结果为分析垂向裂隙各向异性薄煤层地震波传播规律提供工具,为选用相应地震数据进行地震波各向异性参数反演提供依据. 相似文献
10.
地震各向异性介质的群速度是关于相角的复杂函数,将其表示成射线角形式较为困难,这给地震各向异性分析以及走时正演模拟等带来诸多不便;另一方面,观测资料表明实际地球介质的地震各向异性通常较弱,这为用射线角近似表示地震波群速度提供了可能.本文基于以射线角近似表示相角的思想,提出了一种弱各向异性条件下,群速度射线角近似表示的新方法.计算表明,在弱地震各向异性条件下,新方法在很宽的射线角范围内,对三种地震波的群速度都能很好地近似,在准SV波计算精度方面显著优于目前通常使用的近似方法. 相似文献
11.
Seismic waveforms contain valuable information about the media, but the waveform inversion is a non‐linear problem. We present a waveform inversion method that combines a local optimization method with a genetic algorithm to determine the anisotropic parameters of a horizontally stratified medium. Synthetic seismograms for a horizontally stratified anisotropic medium are calculated using the reflectivity technique. In the initial stage of the inversion, the global space‐sampling properties of the genetic algorithm are used to direct the search to the region close to the global solution. This solution is then further improved using a conjugate‐gradient method. The numerical experiments performed with noisy synthetic data show that our hybrid optimization method satisfactorily reconstructs the anisotropic parameters at a reasonable computing cost while the range of slowness is adequate. We found that (i) for small‐angle data neither single‐ nor multiple‐component data are sufficient to determine the anisotropic parameters uniquely; (ii) for medium‐angle data the multiple‐component data are sufficient to determine the anisotropic parameters exactly whereas the single‐component data are not sufficient; and (iii) for wide‐angle data, either single‐ or multiple‐component data are sufficient to determine the anisotropic parameters accurately. 相似文献
12.
We developed an anisotropic effective theoretical model for modeling the elastic behavior of anisotropic carbonate reservoirs by combining the anisotropic self-consistent approximation and differential effective medium models. By analyzing the measured data from carbonate samples in the TL area, a carbonate pore-structure model for estimating the elastic parameters of carbonate rocks is proposed, which is a prerequisite in the analysis of carbonate reservoirs. A workflow for determining elastic properties of carbonate reservoirs is established in terms of the anisotropic effective theoretical model and the pore-structure model. We performed numerical experiments and compared the theoretical prediction and measured data. The result of the comparison suggests that the proposed anisotropic effective theoretical model can account for the relation between velocity and porosity in carbonate reservoirs. The model forms the basis for developing new tools for predicting and evaluating the properties of carbonate reservoirs. 相似文献
13.
基于虚拟偏移距方法的各向异性转换波保幅叠前时间偏移 总被引：2，自引：1，他引：1
In this paper, we use the method of pseudo-offset migration （POM） to complete converted wave pre-stack time migration with amplitude-preservation in an anisotropic medium. The method maps the original traces into common conversion scatter point （CCSP） gathers directly by POM, which simplifies the conventional processing procedure for converted waves. The POM gather fold and SNR are high, which is favorable for velocity analysis and especially suitable for seismic data with low SNR. We used equivalent anisotropic theory to compute anisotropic parameters. Based on the scattering wave traveltime equation in a VTI medium, the POM pseudo-offset migration in anisotropic media was deduced. By amplitude-preserving POM gather mapping, velocity analysis, stack processing, and so on, the anisotropic migration results were acquired. The forward modeling computation and actual data processing demonstrate the validity of converted wave pre-stack time migration with amplitude-preservation using the anisotropic POM method. 相似文献
14.
Chao-ying Bai Tao Wang Shang-bei Yang Xing-wang Li Guo-jiao Huang 《Journal of Seismology》2016,20(2):475-494
Traditional traveltime inversion for anisotropic medium is, in general, based on a “weak” assumption in the anisotropic property, which simplifies both the forward part (ray tracing is performed once only) and the inversion part (a linear inversion solver is possible). But for some real applications, a general (both “weak” and “strong”) anisotropic medium should be considered. In such cases, one has to develop a ray tracing algorithm to handle with the general (including “strong”) anisotropic medium and also to design a non-linear inversion solver for later tomography. Meanwhile, it is constructive to investigate how much the tomographic resolution can be improved by introducing the later arrivals. For this motivation, we incorporated our newly developed ray tracing algorithm (multistage irregular shortest-path method) for general anisotropic media with a non-linear inversion solver (a damped minimum norm, constrained least squares problem with a conjugate gradient approach) to formulate a non-linear inversion solver for anisotropic medium. This anisotropic traveltime inversion procedure is able to combine the later (reflected) arrival times. Both 2-D/3-D synthetic inversion experiments and comparison tests show that (1) the proposed anisotropic traveltime inversion scheme is able to recover the high contrast anomalies and (2) it is possible to improve the tomographic resolution by introducing the later (reflected) arrivals, but not as expected in the isotropic medium, because the different velocity (qP, qSV and qSH) sensitivities (or derivatives) respective to the different elastic parameters are not the same but are also dependent on the inclination angle. 相似文献
15.
考虑地球介质电导率任意各向异性且随空间位置连续变化的情况,本文实现了直接求解电磁场的可控源音频大地电磁测深（CSAMT）三维有限元数值模拟.首先给出了电导率任意各向异性介质中CSAMT二次电场满足的控制方程及其相应变分问题,然后采用任意六面体单元对研究区域进行剖分,在网格单元中对任意各向异性电导率进行线性插值,解决了实际工作中岩矿石电导率各向异性且连续变化的情况,将变分问题转化为线性代数方程组的求解.电导率各向异性且连续变化一维模型三维有限元数值模拟结果与电导率各向异性且分层均匀渐进模型解析解结果对比验证了方法的有效性;三维地电模型电导率随位置线性变化且各向同性、主轴各向异性、方位各向异性和倾斜各向异性的数值模拟结果表明,电导率各向异性且连续变化对CSAMT视电阻率和相位数据均有明显的影响. 相似文献
16.
|v|=v 《地震学报(英文版)》1999,12(4):413-418
IntroductionGenerallyspeaking,theinclusionofanisotropy(exceptdeclaration,anisotropyreferstohomogenousanisotropy)rendersthemathematicalformulationquitecomplicated.Snell'Slawisnotanexceptionandthecalculationofreflectionandtransmissionanglesisnotatrivialtask.ThegraphicalapproachestocalculatingreflectionandtransmissionanglesforanisotropicmediawerepresentedbyAuld(1973)andRokhlin,etal(1986).DaleyandHorn(1977,1979)andSlawinski(1996)deriveSnell'slawintheparticularcasesoftransverselyisotropicandelli… 相似文献
17.
Amir Abbas Babasafari Deva Prasad Ghosh Ahmed Mohammed Ahmed Salim Masoumeh Kordi 《Geophysical Prospecting》2020,68(8):2471-2493
Analysis of amplitude variation with offset is an essential step for reservoir characterization. For an accurate reservoir characterization, the amplitude obtained with an isotropic assumption of the reservoir must be corrected for the anisotropic effects. The objective is seismic anisotropic amplitude correction in an effective medium, and, to this end, values and signs of anisotropic parameter differences (Δδ and Δε) across the reflection interfaces are needed. These parameters can be identified by seismic and well log data. A new technique for anisotropic amplitude correction was developed to modify amplitude changes in seismic data in transversely isotropic media with a vertical axis of symmetry. The results show that characteristics of pre-stack seismic data, that is, amplitude variation with offset gradient, can be potentially related to the sign of anisotropic parameter differences (Δδ and Δε) between two layers of the reflection boundary. The proposed methodology is designed to attain a proper fit between modelled and observed amplitude variation with offset responses, after anisotropic correction, for all possible lithofacies at the reservoir boundary. We first estimate anisotropic parameters, that is, δ and ε, away from the wells through Backus averaging of elastic properties resulted from the first pass of isotropic pre-stack seismic inversion, on input data with no amplitude correction. Next, we estimate the anisotropic parameter differences at reflection interfaces (values and signs of Δδ and Δε). We then generate seismic angle gather data after anisotropic amplitude correction using Rüger's equation for the P-P reflection coefficient. The second pass of isotropic pre-stack seismic inversion is then performed on the amplitude-corrected data, and elastic properties are estimated. Final outcome demonstrates how introduced methodology helps to reduce the uncertainty of elastic property prediction. Pre-stack seismic inversion on amplitude-corrected seismic data results in more accurate elastic property prediction than what can be obtained from non-corrected data. Moreover, a new anisotropy attribute (ν) is presented for improvement of lithology identification. 相似文献
18.
19.
ABSTRACTTurbulence in the Earth's outer core not only increases all diffusive coefficients, but it can lead to their anisotropic properties. Therefore, the model of rotating magnetoconvection in horizontal plane layer rotating about vertical axis and permeated by homogeneous horizontal magnetic field, influenced by anisotropic diffusivities, viscosity and thermal diffusivity, is advanced by considering the magnetic diffusivity as anisotropic too. The case of full anisotropy, i.e. all coefficients anisotropic, is compared with both the case possessing isotropic diffusion coefficients and the case of partial anisotropy, i.e. mixed case with isotropic and anisotropic diffusive coefficients (viscosity and thermal diffusivity anisotropic and magnetic diffusivity isotropic). The existence and preference of instabilities is sensitive to all non-dimensional parameters, as well as on anisotropic parameter, the ratio of horizontal and vertical diffusivities. Two types of anisotropy, BM (introduced by Braginsky and Meytlis) and SA (stratification anisotropy) are studied. BM as well as SA were applied by ?oltis and Brestenský to the study of the partial anisotropy; this study is extended, in this paper, to full anisotropy cases (full SA and full BM) and it is shown that the style of convection given by the onset of stationary modes is more affected by anisotropic diffusivities in BM than in SA anisotropy. The important influence of strong anisotropies in the Earth's core dynamics is stressed. 相似文献
20.
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