Automatic identification of fake patterns caused by short-width wavelets in seismic data

Despite the popularity of using the Haar wavelet filter in many applications, it sometimes introduces fake patterns into the multi resolution analysis (MRA) of seismic data. In this work, we compared different wavelet filters to demonstrate that these patterns are fake and not part of the original waveforms and to show that they are a result of using the Haar wavelet filter as a short-width wavelet. To achieve this, many seismic waveforms from two different sources: the Egyptian National Seismic Network (ENSN) and the High Sensitivity Seismograph Network Japan (Hi-net) are used with different wavelet filters. We propose an algorithm based on an autoregressive (AR) model to detect these patterns automatically and fully.     

综合地震勘探方法在陕北煤田采空区探测中的应用

基于陕北黄土塬煤层采空区地震勘探方法研究项目,在该类复杂地质背景和地震地质条件下进行了煤层采空区多种地震探测方法的应用。探测中依据不同的地震勘探方法原理,针对同一目标地质体,提取了识别其地震波场的响应特征:①在地震反射时间剖面上呈现反射波组中断缺失、不连续特征;②在折射层析速度剖面上反射为低速异常;③面波记录出现强能量基阶面波传播中止(波散),面波速度剖面呈现为低速异常,频散曲线发生畸变(呈"之"字型回折);④煤层采空区边界显现出散射波特征。这些地震波场特征在鄂尔多斯等地的煤层采空区探测中也已得到验证。陕北煤田采空区探测实例表明,采用综合地震勘探方法探测可有效解决单一方法的多解性问题,提高其成果的准确性和可靠性。     

Estimation of semivariograms by the maximum entropy method

A wide variety of semivariograms may be represented in terms of a first- or second-order autoregressive (AR) process, and the nugget effect may be included by use of a moving average (MA) process. The weighting parameters for these models have a simple functional dependence on the value of the sill and the semivariance at the first and second lag. These may be estimated either graphically from the semivariogram or directly from the computed values. Improved spectral estimates of geophysical data have been obtained by the use of the maximum entropy method, and the necessary equations were adapted here for the estimation of the weighting parameters of the AR and the MA processes. Comparison among the semivariograms obtained for the ideal case, the observed case, and the estimated case for artificial series show excellent correspondence between the ideal and estimated while the observed semivariogram may show marked divergence.     

Deterministic ensemble smoother with multiple data assimilation as an alternative for history-matching seismic data

This paper reports the results of an investigation on the use of a deterministic analysis scheme combined with the method ensemble smoother with multiple data assimilation (ES-MDA) for the problem of assimilating a large number of correlated data points. This is the typical case when history-matching time-lapse seismic data in petroleum reservoir models. The motivation for the use of the deterministic analysis is twofold. First, it tends to result in a smaller underestimation of the ensemble variance after data assimilation. This is particularly important for problems with a large number of measurements. Second, the deterministic analysis avoids the factorization of a large covariance matrix required in the standard implementation of ES-MDA with the perturbed observations scheme. The deterministic analysis is tested in a synthetic history-matching problem to assimilate production and seismic data.     

Multi-resolution clustering analysis and 3-D visualization of multitudinous synthetic earthquakes

We use modern and novel techniques to study the problems associated with detection and analysis of multitudinous seismic events, which form the background for isolated great earthquakes. This new approach involves multivariate analysis of low and large magnitude events recorded in space over a couple of centuries in time. We propose here the deployment of the clustering scheme both for extracting small local structures and large-scale trends in synthetic data obtained from four numerically simulated models with: uniform properties (U), a Parkfield-type asperity (A), fractal brittle properties (F), and multi-size-heterogeneity fault zone (M). The mutual nearest neighbor (mnn) clustering scheme allows for extraction of multi-resolutional seismic anomalies in both the spatio-temporal and multi-dimensional feature space. We demonstrate that the large earthquakes are correlated with a certain pathway of smaller events. Visualization of the anomalies by using a recently introduced visualization package Amira reveals clearly the spatio-temporal relationships between clusters of small, medium and large earthquakes, indicating significant stress relaxation across the entire fault region. We demonstrate that this mnn scheme can extract distinct clusters of the smallest events, which precede and follow a singularly large magnitude earthquake. These clusters form larger spatio-temporal structures comprising a series of large earthquakes. The link between the large and medium magnitude events is not so clearly understood. Short-ranged correlations are dominated by strong spatio-temporal anomalies, thus reflecting the global seismic properties of the entire fault zone.Electronic Supplementary Material Supplementary material is available for this article if you access the article at . A link in the frame on the left on that page takes you directly to the supplementary material.     

Upper bound finite element analysis of slope stability using a nonlinear failure criterion

In this study, upper bound finite element (FE) limit analysis is applied to stability problems of slopes using a nonlinear criterion. After formulating the upper bound analysis as the dual form of a second-order cone programming (SOCP) problem, the stress field and corresponding shear strength parameters can be determined iteratively. Thus, the nonlinear failure criterion is represented by the shear strength parameters associated with stress so that the analysis of slope stability using a nonlinear failure criterion can be transformed into the traditional upper bound method with a linear Mohr–Coulomb failure criterion. Comparison with published solutions illustrates the accuracy and feasibility of the proposed method for a simple homogeneous slope stability problem. The proposed approach is also applied to a seismic stability problem for a rockfill dam to study the influence of different failure criterions on the upper bound solutions. The results show that the seismic stability coefficients obtained using two different nonlinear failure criteria are similar but that the convergence differs significantly.     

一种基于压缩感知的随机噪声压制方法

随着高精度地震勘探技术的发展,利用高保真的方法提高地震资料信噪比成为了去噪处理的关键。曲波域阈值法能够有效地压制随机噪声,但易产生伪吉布斯震荡现象,造成信号局部畸变,从而影响处理效果。针对这一问题,提出一种基于压缩感知理论（Compressing Sensing,简称CS）的地震信号去噪方法,该方法利用随机噪声和有效信号在曲波稀疏域稀疏表征的差异来分离随机噪声。其实现步骤为:将地震数据变换到曲波域;利用压缩感知理论和全变差正则化算法重构曲波系数;曲波逆变换得到压制噪声后的重构地震数据。理论模型和实际资料应用表明,该方法能够很好规避伪吉布斯现象带来的信号失真问题,进一步提高了资料的信噪比。      

互相关与最小二乘加权目标函数全波形反演

全波形反演是一个高度非线性的优化问题,当地震数据中缺少低频成分而初始速度与真实速度相差较远时,反演容易陷入局部极小值。笔者提出一种新的目标函数,将模拟地震记录和观测记录的归一化互相关与最小二乘结合。互相关侧重相位匹配,具有更强的线性,能减弱"跳周"现象。通过设置权重因子,在反演前期利用互相关先恢复低波数的背景速度模型,再加入最小二乘约束恢复高波数的模型细节。数值模拟试验结果表明,基于该目标函数的全波形反演不依赖精确的初始模型和低频信息,向全局极小值迅速收敛,能有效改善反演的稳定性,并获得比基于常规目标函数的全波形反演更精确的结果。     

Kinematical analysis of 3D passive earth pressure with nonlinear yield criterion

Conventional methods for calculation of passive earth pressure were mainly based on the assumptions of the linear Mohr‐Coulomb yield condition and plane strain failure mechanism. However, both theoretical and experimental studies have shown that such assumptions are not satisfied in some geotechnical projects. Herein, a novel method incorporating a kinematically admissible 3‐dimensional (3D) rotational failure mechanism and the nonlinear power‐law yield criterion is proposed to compute the passive earth pressure acting on the inclined retaining walls. Instead of using the nonlinear yield criterion directly, a straight line tangential to the nonlinear yield curve is employed to represent the strength of soils, and therefore, the nonlinear problem is transformed into the traditional linear problem. The 3D failure mechanism is generated through rotating a circle defined by 2 log‐spirals, and a plane strain block is inserted into the mechanism to consider the retaining walls with different widths. Earthquake effects are taken into account by using quasi‐static representation, and the horizontal seismic coefficient concept is adopted for the estimation of passive earth pressure under seismic conditions. An analytical expression about the 3D passive earth pressure is educed by means of the upper bound theorem of limit analysis. Numerical results for different practical parameters are obtained from an optimization scheme where the minimum of passive earth pressure is sought. Compared with available 2‐dimensional and 3D solutions, the proposed method is validated. A parametric study is conducted to investigate the effects of different parameters on the 3D static and seismic passive earth pressure.     

Seismic waves and correlation autoregressive processes

Stochastic models appropriate for seismic records of earthquakes and underground nuclear explosions are considered and a selective review of the existing models is presented. Special models of stationary processes, periodically correlated processes, and uniformly modulated stationary processes as well as a new class called correlation autoregressive processes are studied. Relevant properties of correlation autoregressive processes are presented. It is shown that the successful models presently used are all subclasses of the correlation autoregressive processes. Shortcomings of the existing nonstationary models and merits of the new class for seismic wave modeling are discussed and directions for the further research and development are suggested. It is hoped that the model and the ideas introduced in this article will provide a stimulation for further examination of correlation autoregressive processes and will promote statistical modeling of seismic records.     

基于相对熵的时差相位差自动识别校正方法

针对地震资料处理中存在的时差、相位差问题,提出了一种时差、相位差自动识别校正方法.该方法以希尔伯特变换和相对熵算法为理论基础,以KL散度为判别准则,全过程数据驱动,自动化实现时差、相位差的识别与校正,有效降低人工识别成本,避免人为因素带来的误差.文中详细阐述了相关原理及实施过程,并通过数值模拟结果验证了该方法的正确性和...     

一种基于AR 模型的预测滤波压制随机噪声方法

在地震勘探中,随机噪声是一类不可避免的噪声,它的存在极大地降低了地震资料的信噪比,导致偏移成像效果差甚至不能成像。自适应线性预测滤波方法是在时间--空间域自回归( AR) 模型系数变化的假定下,把自回归( AR) 模型数学表达式进行变换,引入代价函数以提高解的稳定性、唯一性,推导得到压制一维和二维随机噪声的递归算法。通过模拟和实际地震资料验证表明,该方法能较好地压制低信噪比资料中的随机噪声干扰,同时能较好地保护有效地震信号。     

The generation of multidimensional autoregressive series by the herringbone method

The generation of isotropic artificial series in two or three dimensions by the autoregressive process is of considerable interest for the purpose of modeling environmental properties such as ore grade or reservoir porosity. The relations needed to produce bilateral symmetry using the one-sided autoregressive recursion equations have been attained on the square net and on the isometric lattice by an alternation procedure. In the case of the square net, the one-sided autoregressive (AR) process is alternated between the two diagonals of the net, while in three dimensions, the alternation takes place among the four body diagonals of the isometric cell.     

初至折射波静校正技术在复杂探区地震数据处理中的应用

山区及黄土塬地区近地表结构复杂，地形起伏大、低降速带横向变化剧烈，地震资料处理中的静校正难度加大。长波长静校正容易引起构造形态畸变，短波长静校正影响地震剖面信噪比。针对此类问题，从长波长静校正问题及短波长地表非一致性问题分析入手，提出部分炮检距叠加识别长波长静校正技术及分段统计逼近地表非一致性校正技术。该技术在复杂地表区与其它相关技术综合应用，可有效解决长、短波长静校正问题。     

基于小波包能量谱的建（构）筑物爆破地震安全评估

基于现场实测爆破振动数据,采用小波包分析技术对爆破振动信号进行了时频特征分析。根据小波包变换的分层分解关系,推导出爆破振动信号不同频带的小波包频带能量,小波包频带能量能同时反映爆破振动3要素（振动的强度、频率和持续时间）的作用影响。基于小波包能量谱,获得了爆破振动信号不同频带能量的分布特征,根据受控结构体对爆破振动动态响应特性,首次建立了能考虑爆破振动3要素以及受控建（构）筑物本身的动态响应特性（固有频率和阻尼比）等因素综合的安全判据--响应能量判据,并用工程实例验证了该判据的可行性和可靠性。该判据较之现行的速度-频率安全判据来说,能准确地描述爆破振动对受控建（构）筑物的影响程度,更能全面地评估建（构）筑物爆破地震效应。     

地震资料处理中的Radon变换及反Q滤波

Radon变换利用信号的横向相关性和信号根幅随炮检距变化的特征,提取有效反射信号同相轴,同时提取的零炮检距地震剖面,保留了地震记录的高频信息,达到了提高分辨率的目的。叠前反Q滤波是以FUTTERMAN衰减模型为理论基础,校正地震子波相位拉伸,补偿地震波频率和振幅的损失,达到提高地震资料分辨率和信噪比及改善同相轴连续性的目的。      

合成孔径雷达对地观测应用中目标感兴趣区域的自动获取

在简要评述国内外对地观测应用中,利用SAR图像进行目标ROI的自动获取方面的研究成果及存在问题的基础上,提出了一种SAR图像目标ROI自动获取新方案,包括SAR图像自动目标检测方案和SAR图像自动目标鉴别方案并解决其中的关键技术。实测数据的实验结果证明了新方案具有稳健性强、适用性广、自动化程度高、计算量小、工程实现易等特点,说明了该方案对于空间对地观测具有广泛的应用前景。     

EARTHQUAKE ANALYSIS OF GRAVITY DAMS BASED ON DAMAGE MECHANICS CONCEPT

In this paper, the seismic response analysis of concrete gravity dams is presented using the concept of Continuum Damage Mechanics. The analysis is performed using the finite element technique and a proper material degradation/damage model. The damage criterion used here is a second order tensor model based on elastic-brittle characterization and on a power function of the principal tensile stress. The methodology employed is shown to be computationally efficient and consistent in its treatment of both damage growth and propagation. Other important features considered in the analysis are: (1) dam–foundation interaction (2) appropriate modelling of joined rock mass using continuum damage mechanics, and (3) proper modelling of unbounded domain of foundation rock. The infinite media representation of the foundation material has been achieved by using doubly asymptotic approximation. The results of the analysis indicate that the seismic response of a damaged concrete dam could be significantly different from that of an undamaged one. In particular, the analysis shows that during a seismic event, the microstructure of a damaged zone can significantly change due to growth and propagation of microcracks.     

地震层位自动追踪技术研究

在地震勘探中,地震层位解释是地震解释的基础工作,而层位的识别和追踪是地震层位解释的一个很重要的环节。由于过去的层位追踪基本上是纯手工,既耗时又耗力,而地震层位反映在地震波形上具有同相性和相似性等,这使得依据地震波形的这些性质,研究某种算法让计算机自动追踪层位成为可能。这里介绍了两种层位自动追踪方法：波形特征追踪算法和相关追踪算法,并分别分析了这两种算法的原理。通过编程实现了这两种方法,对它们的追踪效果进行了对比分析和总结,两种方法总体上满足层位追踪要求,结合应用两种方法能够达到很好的效果。     

ARMA order model detection using minimum of Kurtosis: application on seismic data

The objective of this study is to find the order and coefficients of non-low-phase causal filters for ARMA (auto regressive moving average) filter model, using the Kurtosis minimization criterion. This method is based on the Kurtosis calculation of the treated sample at the input level and its identification at the output of the ARMA model. For this purpose, the order and coefficients of the AR (auto regressive) part are identified using the Yule-Walker algorithm at order two and then extended to order four. To obtain the MA (moving average) part, the AR components are calculated at first from the ARMA filter by deconvolution. Then, spectrally equivalent and minimum phase (SEMP) MA filter is identified using the Durbin algorithm at second and fourth order. Finally, the correct filter is found when the Kurtosis value of the output ARMA filter reconstituted is the closest to the Kurtosis of introduced signal. The proposed method is then tested on simulated processes and applied to real seismic data to perform blind deconvolution and obtain the reflectivity coefficients of subsoil studied.