Constrained inversion and the generalized reciprocal method: on the ambiguity in the estimation of velocity structure and depths of discontinuities, hidden layers and low-velocity zones     

J. C. V. Traslosheros 《Geophysical Journal International》1997,128(3):659-675

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P-SH conversions in a flat-layered medium with anisotropy of arbitrary orientation   总被引：3，自引：0，他引：3  

Vadim Levin  Jeffrey Park 《Geophysical Journal International》1997,131(2):253-266

P-SH conversion is commonly observed in teleseismic P waves, and is often attributed to dipping interfaces beneath the receiver. Our modelling suggests an alternative explanation in terms of flat-layered anisotropy. We use reflectivity techniques to compute three-component synthetic seismograms in a 1-D anisotropic layered medium. For each layer of the medium, we prescribe values of seismic velocities and hexagonally symmetric anisotropy about a common symmetry axis of arbitrary orientation. A compressional wave in an anisotropic velocity structure suffers conversion to both SV -and SH -polarized shear waves, unless the axis of symmetry is everywhere vertical or the wave travels parallel to all symmetry axes. The P-SV conversion forms the basis of the widely used 'receiver function' technique. The P-SH conversion occurs at interfaces where one or both layers are anisotropic. A tilted axis of symmetry and a dipping interface in isotropic media produce similar amplitudes of both direct ( P ) and converted ( Ps ) phases, leaving the backazimuth variation of the P-Ps delay as the main discriminant. Seismic anisotropy with a tilted symmetry axis leads to complex synthetic seismograms in velocity models composed of just a few flat homogeneous layers. It is possible therefore to model observations of P coda with prominent transverse components with relatively simple 1-D velocity structures. Successful retrieval of salient model characteristics appears possible using multiple realizations of a genetic-algorithm (GA) inversion of P coda from several backazimuths. Using GA inversion, we determine that six P coda recorded at station ARU in central Russia are consistent with models that possess strong (> 10 per cent) anisotropy in the top 5 km and between 30 and 43 km depth. The symmetry axes are tilted, and appear aligned with the seismic anisotropy orientation in the mantle under ARU suggested by SKS splitting.  相似文献   

Time-domain electromagnetic migration in the solution of inverse problems   总被引：5，自引：0，他引：5  

Michael S. Zhdanov  Oleg Portniaguine 《Geophysical Journal International》1997,131(2):293-309

Time-domain electromagnetic (TDEM) migration is based on downward extrapolation of the observed field in reverse time. In fact, the migrated EM field is the solution of the boundary-value problem for the adjoint Maxwell's equations. The important question is how this imaging technique can be related to the solution of the geoelectrical inverse problem. In this paper we introduce a new formulation of the inverse problem, based on the minimization of the residual-field energy flow through the surface or profile of observations. We demonstrate that TDEM migration can be interpreted as the first step in the solution of this specially formulated TDEM inverse problem. However, in many practical situations this first step produces a very efficient approximation to the geoelectrical model, which makes electromagnetic migration so attractive for practical applications. We demonstrate the effectiveness of this approach in inverting synthetic and practical TDEM data.  相似文献   

Comment on 'Estimation of resolution and covariance for large matrix inversions' by J. Zhang and G. A. McMechan     

M. M. Deal  G. Nolet 《Geophysical Journal International》1996,127(1):245-250

When inverting large matrices, iterative techniques are necessary because of their speed and low memory requirements, as opposed to singular value decomposition (SVD). Recently, there have been attempts to obtain information on the quality of the solutions calculated using conjugate gradient (CG) methods such as LSQR. The purpose of this note is to comment on the paper titled "Estimation of resolution and covariance for large matrix inversions' by Zhang & McMechan (1995), who extend Paige and Saunders' LSQR algorithm to obtain an orthonormal basis used to approximate resolution and covariance. We show that for larger problems, where the number of orthogonal vectors is several orders of magnitude smaller than the number of model parameters, the vectors obtained do not adequately span the range of the model space. We use a synthetic borehole experiment to illustrate the differences between the singular value spectrum obtained through the more complete method of SVD and the Ritz value spectrum that results from a simple extension of LSQR, We also present a trivial numerical example to illustrate the differences between Zhang & McMechan's approximate resolution matrix and the true resolution.  相似文献   

Shear-wave velocity structure beneath Europe, the northeastern Atlantic and western Asia from waveform inversions including surface-wave mode coupling   总被引：6，自引：0，他引：6  

Henk Marquering  Roel Snieder 《Geophysical Journal International》1996,127(2):283-304

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用非线性遗传反演方法进行自动静校正   总被引：4，自引：0，他引：4       下载免费PDF全文

姚姚 《地球科学》1996,21(1):89-92

静校正处理是消除近地层影响的一个重要地震资料数字处理方法，在近地表层纵，横向变化复杂，静校正量变化较大的地区，常规静校正方法和线性反演方法均不能解决问题，遗传算法是近年发展起来的一种模拟生物生化过程的较先进的非线性反演方法，对用遗传算法进行静校正的若干问题进行了讨论，说明它是可以解决表层情况复杂地区静校正问题的一个有效方法。  相似文献   

混合岩中斜长石的交代净边结构和倒转双晶研究——以大别罗田黄土岭长英片麻岩为例   总被引：3，自引：0，他引：3  

游振东  钟增球  汤中道  陈能松 《地球科学》1996,(5)

湖北罗田黄土岭长英片麻岩是与紫苏石榴黑云片麻岩共生的浅色片麻岩，成分上近于Ａ型花岗岩．受到浅混合岩化，钾交代现象显著．在斜长石与钾长石新成体接触处有清楚的交代净边结构，背散射电子探针分析表明，净边成分为钠长石（Ａｂ８９～９７）．在净边结构上，发现叠加倒转双晶．净边结构产生于长英片麻岩部分熔融的高温条件下，与整个大别地体隆升过程和Ａ型花岗岩的生成有成因联系  相似文献   

西藏羌塘地区几个地质构造问题   总被引：5，自引：1，他引：5  

李才  和钟铧  杨德明 《世界地质》1996,(3)

提出了西藏羌塘地区的六个地质构造问题。包括冈瓦纳与欧亚大陆古特提斯界线；羌塘地区是否存在加里东期或更古老基底；羌塘地区的地层系统及其对比；狮头山、黑熊山一带蓝片岩的地球动力学意义；龙木错─双湖蛇绿岩的性质、成因及年代；羌塘盆地中三叠世以前是一个统一的盆地还是分属两大陆的边缘海盆等。这些问题的解决将有助于更加清楚、完整地认识青藏高原的地质历史过程。  相似文献   

论广义逆矩阵阶数增大的递推算法     

蔡宗熹  蔡越虹 《物探化探计算技术》1996,18(2):113-117

本文针对加拿大地球物理学家ＥｄｏＮｇｌａｎｄ教授提出的问题，对Ｍ—Ｐ广义逆矩阵的递推算法进行了探分论述探讨的初步结果和对Ｇｒｅｖｉｌｌｅ递推算法的扩充。文中对算法的扩充给出严格的证明。  相似文献   

Barotropic local instability and severe storm process     

Dasheng Yang  Lan Sun 《中国科学D辑(英文版)》1997,40(3):259-268

By means of barotropic model, the characteristic and initial value problems are investigated to reveal the local two-dimensional barotropic instability of the nonuniform current to the dynamic mechanism of the formation of the Yangtze-Huaihe River severe storm in July 1991. Analytical theory and numerical experiment show that (i) the unstable developing modes are chiefly the two periods of about 44 d and 10 d, which are fundamentally consistent with that of the precipitation change of the Yangtze-Huaihe River. (ii) The growth rate of the local perturbation is dominated by the meridional wave numbern = 1–5 and zonal wave numberk = 1–12, i.e. the severe storm over the Yangtze-Huaihe River results from the interaction of the systems at different latitudes and waves of different scales, (iii) The perturbation over the Yangtze-Huaihe River possesses the property of local intensification, which slowly migrates westward over the lower and middle reaches of the Yangtze-Huaihe River. (iv) The growth rate of the instability, especially the propagation velocity of the perturbation, is sensitive to the external parameters ū and α. Project supported by the National Natural Science Foundation of China.  相似文献