S变换谱分解技术在深反射地震弱信号提取中的应用

在深反射地震资料处理中,当来自深部的有效弱信号和噪声干扰频带差异较小且难以区分时,传统滤波方法的应用会受到限制.谱分解方法是一种使用离散傅里叶变换,基于信号的频率-振幅谱等信息生成高分辨率地震图像的方法,通常用来识别介质物性横向分布特征,处理复杂介质内频谱变化和局部相位的不稳定性等问题,包括定位复杂断层和小尺度断裂等.S变换作为一种新的时频分析方法,具有自动调节分辨率的能力,近些年来被广泛应用到勘探地震、大地电磁等数据处理中,逐渐成为地球物理方法中噪声压制的有效方法之一.与常规石油反射地震资料相比,深反射主动源地震为了探测深部结构信息,常采用大药量激发方式、长排列观测系统等,导致深部有效信号基本湮灭在噪声干扰之中.针对深反射数据特点,本文结合谱分解和S变换技术,首先设计了简单的脉冲函数实验数据,证实S变换方法的有效性,同时说明谱分解方法的效果受所用时频分析方法影响较大,而其中决定分辨能力的变换窗函数的选取尤为重要.在此基础上,分别应用到深反射地震资料的单道和叠加剖面实际数据上,对比分析了传统变换谱分解和S变换谱分解的应用效果,单道资料对比结果表明:相比传统谱分解,S变换谱分解方法具有自动调节分辨率的能力,能够精确的标定深反射地震资料中弱信号不同时刻的频率分量; 叠加剖面资料应用结果表明:由S变换谱分解得到的剖面结果与其他谱分解方法结果整体上具有较高的一致性,同时清晰地刻画出原叠加剖面上被噪声湮灭的低频细节特征,提高了剖面的分辨率及同相轴连续性;对比结果明显看出,Gabor变换谱分解方法得到的结果同相轴较为破碎,分析原因认为这是由Gabor变换的时频分解方法的定长窗函数所致,窗口大小不会随着信号频率的变化来调节长度,只能在处理的过程中根据一定的记录长度范围选取窗函数参数,而S变换谱分解方法在窗函数的选取时,通过时变信号的局部频率特征自动调节窗口长度,能够更好的刻画各个频段的细节特征,在深反射剖面成像应用中效果尤为明显.本文结果表明S变换谱分解技术在深地震叠加剖面上的应用有效地提高了来自深部弱反射信号的信噪比和分辨率,并刻画出了叠加剖面上所不具有的低频细节特征,在实际深反射地震资料处理中能有效保护低频弱信号获得更好的成像效果.本文为深地震反射资料中弱信号的保护处理找到一种有效的方法.     

大型积分方程降阶解法与重力资料曲面延拓

分析了等效源曲面延拓方法积分方程核函数的自相似性、冗余性,根据Fredholm积分方程核函数特征,提出了一种小波余弦非线性阈值压缩算法,实现了大型Fredholm积分方程的降阶,使得Bhattacharyya等（1977年）提出的等效源曲面延拓方法能够处理大面积、大数据量的资料. 理论模型结果表明,当压缩比为40.5%时硬阈值压缩方法的曲面延拓可以达到很高的精度,当压缩比为81.1%时, 硬阈值压缩方法精度降低,而采用我们提出的余弦非线性阈值可以明显提高曲面延拓的精度. 将硬阈值、软阈值和非线性阈值压缩三种不同方法用于川东北气田MT－1线资料的处理,当压缩比达79%时,三种不同方法曲化平结果都可以达到很好的效果,但非线性阈值压缩的曲化平结果失真最小,它能够客观地反映杨家河局部隆起,为在该区寻找与油气有关的局部构造提供重要依据.     

小波变换在少震、弱震区地下水位数据分析中的应用

利用小波变换和多尺度分析原理，对位于少震弱震区的湖南的具有不同变化形态的6口典型井4年的水位日均值序列进行了分析。结果显示，通过多尺度分析可以很方便地将水位日均值序列中的高频部分与低频部分分开，而且对不同井孔的含水层系统而言，分离出去的频率成分的主模是不同的，这反应出不同井孔的含水层系统对同一频率的响应存在差异，主模的频率反映了正常背景下井孔－含水层系统的优势频率。Morlet小波分析的结果对时间序列的突然变化和周期结构都有很好的反映。     

The application of combined gravity and seismic data formation separation for revealing deep structure

In some oilfields with 3D seismic data, the deeper structure cannot be observed due to poor quality deep seismic data. Layer stripping using both seismic and gravity data is a solution for this problem but it cannot get satisfactory results because the horizontal variations in formation density are ignored. We present a variable-density formation separation technique to address this problem. Based on 3D seismic depth data and laterallyvariable density derived from 3D seismic velocity data, the upper formation gravity effect is calculated by forward modeling and removed from the Bouguer gravity. The formation-separated gravity anomaly with variable density is obtained, which mainly reflects the deeper geological structure. In block XX of North Africa, the shallow formations seismic data is excellent but the data at the top of basement is poor. The formation-separated gravity anomaly processed under the control of 3D seismic data fits well with the known seismic interpretation and wells. It makes the geological interpretation more reliable.     

重力-地震联合变密度剥层技术研究深层构造

在某些已经完成三维地震勘探工作的油气田区,因深层地震资料不好,深层构造难以得到解决。虽然结合地震资料与重力资料的重力剥皮技术得到开发和使用,但由于它没有考虑地层密度的横向变化,因此未能获得满意的处理效果。为了改善该类地区的重力勘探效果,本文提出了变密度剥层方法,它利用各地层的三维地震深度资料和三维地震层速度转换的具横向变化的密度资料,通过正演其重力效应,并从布格重力异常中去除,从而得到主要反映深部地质构造信息的变密度剥层重力异常。在北非某区块,除基底顶面外,各层地震资料良好,通过重力-地震联合变密度剥层处理得到的剥层重力异常,与已知地震和钻井资料吻合良好,为深部基底研究奠定了良好的基础。     

The R-approximation method and its application to the interpretation of detailed gravity and magnetic data

The application of the R-approximation method based on the use of the Radon integral transform within the framework of the method of linear integral representations to the interpretation of detailed gravity and magnetic data is considered in this paper. The results are presented for some research areas located in Russia and in the Crimea (Ukraine). The method determines the distribution of anomalous field elements, construction of the analytical continuation of fields, and their linear transformations with a sufficiently high degree of accuracy.     

考虑我国场地土类型的弹塑性反应谱法在高层混合结构中的应用

弹塑性反应谱法中,强度折减系数、延性系数、周期之间的关系模型（R—μ—T关系）是影响计算结果的一个重要参数。各国学者考虑不同地震动记录、滞回模型、场地土条件、阻尼比等参数,提出了不同的模型,但在场地特征对关系影响上存在不同认识。本文按考虑我国场地土类型的模型,分别进行了某高层混合结构在设防7度、7．5度、8度、8．5度、9度下的弹塑性反应谱计算,得到了一系列结构最大层间位移角,并与增量动力分析（IDA）的结果进行了对比。分析表明,考虑我国场地土类型的高层混合结构弹塑性反应谱计算结果与IDA分析50％均值曲线吻合较好。本文计算结果可为弹塑性反应谱法在复杂高层结构中的应用提供基础。     

消除滑动扫描地震数据中谐波干扰的反相关方法(英文)

滑动扫描技术是高效、高保真、环保的可控震源勘探技术之一,是下一组震源不必等待上一组震源震动结束即可开始震动的高效采集方法。该技术由于缩短了相邻两炮的等待时间,使得生产效率得到显著提高。但是后一炮的谐波畸变与前一炮的基波信号混叠在一起,不易分离,在相关后的地震记录上形成了严重的谐波干扰,降低了地震资料的质量。本文提出一种反相关方法来压制滑动扫描地震数据中的谐波干扰。该方法首先把地面力信号分解为基波和各阶谐波分量;然后将后一炮的相关前数据分别与各分量相关,只选取正时间轴中对应分量的自相关部分,利用各分量的反相关算子提取各阶谐波信息;最后从前一炮数据中减去提取出的高阶谐波,得到压制谐波后的地震记录。该方法对有效信号影响小,可同时处理相关前和相关后数据,而且算法简单稳定,计算效率高。本文分别对理论模型和实际数据进行处理,验证了该方法消除谐波干扰的有效性。     

Improved NMO correction with a specific application to shallow-seismic data

The application of traditional NMO‐correction techniques in the processing of seismic data may result in severe distortion. This distortion is observed as a decrease in frequency content (NMO stretch) or even a total loss of data for steep velocity gradients. It is shown that the specific nature of the observed distortion is introduced by the particular implementation of the traditional NMO‐correction technique. It is also shown that other techniques that have been proposed in the literature suffer from similar artefacts. An alternative approach is suggested, based on the correction of tapered blocks of seismic data, followed by a coherence filter to compensate for the specific artefacts thus introduced. Correction of seismic amplitudes (e.g. geometrical spreading and attenuation) is implemented as an integral part of the NMO‐correction method thus allowing for both dynamic and kinematic reconstruction of interfering events. From the application of this method to synthetic and field data, it is concluded that the proposed technique may be particularly useful in the processing of shallow seismic (shear‐wave) data. Although not illustrated in this paper, it is emphasized that application of the proposed method is by no means restricted to shear waves; application to P‐wave data will prove equally useful, although the stretch effects involved may not be as severe as in the examples given in this paper.     

The inverse study of crustal damage state with gravity data in frequency domain

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双层界面重磁联合反演方法研究

Based on the synchronous joint gravity and magnetic inversion of single interface by Pilkington and the need of revealing Cenozoic and crystalline basement thickness in the new round of oil-gas exploration, we propose a joint gravity and magnetic inversion methodfor two-layer models by concentrating on the relationship between the change of thicknessI and position of the middle layer and anomaly and discuss the effects of the key parameters. Model tests and application to field data show the validity of this method.     

多源布格重力异常数据贝叶斯融合算法及其在川滇地区的应用

布格重力异常数据是研究地壳结构和变形的重要依据,由于观测手段、处理方法等存在差异,不同手段获得的布格重力异常可能存在数据噪声水平及起算基准不一致,从而引起多源布格重力异常数据难以有效融合的难题.为此,本文在传统等效源重力数据融合方法的基础上,通过引入贝叶斯参数优化准则,提出了一种新的多源布格重力异常融合算法.随后对川滇...     

青藏高原构造结构特点:新重力异常成果的启示

截至2007年1:1000000区域重力工作已基本覆盖青藏高原全区,这些全新的重力成果揭示了很多有意义的现象.通过多方法处理分析研究不同深度层次的重力场特征及正反演计算构建地壳模型,认为:重力异常形态显示青藏高原独成体系,与相邻块体具有多样化的接触关系.已发现蛇绿岩的结合带、弧盆系和岩浆岩带是幅值不等、规模不一的重力高和重力低,表明青藏高原是具有多条结合带的拼合体;班公湖—怒江结合带是高原内最主要的重力高异常带,长达千余公里,将不同深度层次的重力场分成截然不同的南北两大区块,为它是冈瓦纳大陆北界提供了依据;局部重力异常指示青藏高原构造形迹自南而北以东西走向为主,东部则为北西—南北走向,具有与大地构造相似的分区特征; 85°E和92°E附近存在较大尺度的南北和北东走向的重力异常特征线,揭示出青藏高原腹地的深部结构具有东中西三分现象,与表壳的东西走向格局形成对比.     

Revisiting the Phasor-Walkout method for detailed investigation of harmonic signals in time series

A well-known but rarely used powerful method to investigate the presence of harmonic signals in time series is the Phasor Walkout method (other names are: Graphical Fourier Transform, Summation Dial, Complex Demodulation). At a given test frequency the complex contributions (phasors) to the Fourier Transform of each sample in an equidistantly sampled series are added vectorially in the complex plane. The resulting pattern, the walkout, reveals information about the properties of the signal which is not easy to obtain by other methods. Synthetic examples are used to demonstrate the resolving power of the method. The following geophysical examples for the application of this method are shown: determination of the frequency of the breathing mode₀ S ₀ of the earth after a large earthquake; the study of superconducting gravimeter records after a large deep earthquake used in the core mode interpretation of a spectral peak, the study of the residualS ₃ (8 h period) signal in a tidal record and the bichromatic Rayleigh-waves from Mount Pinatubo on June 15, 1991.     

Change in the spectrum of a gravity anomaly caused by expressing it discretely

Summary The spectral content of an operation which may be called the operation of selecting the step for treating a certain, discretely expressed datum, continuous by nature is shown.     

Gravity reduction with three-dimensional atmospheric pressure data for precise ground gravity measurements

The redistribution of air masses induces gravity variations (atmospheric pressure effect) up to about 20 μgal. These variations are disturbing signals in gravity records and they must be removed very carefully for detecting weak gravity signals. In the past, different methods have been developed for modelling of the atmospheric pressure effect. These methods use local or two-dimensional (2D) surface atmospheric pressure data and a standard height-dependent air density distribution. The atmospheric pressure effect is consisting of the elastic deformation and attraction term. The deformation term can be well modelled with 2D surface atmospheric pressure data, for instance with the Green's function method. For modelling of the attraction term, three-dimensional (3D) data are required. Results with 2D data are insufficient.From European Centre for Medium-Range Weather Forecasts (ECMWF) 3D atmospheric pressure data are now available. The ECMWF data used here are characterised by a spacing of Δ and Δλ = 0.5°, 60 pressure levels up to a height of 60 km and an interval of 6 h. These data are used for modelling of the atmospheric attraction term. Two attraction models have been developed based on the point mass attraction of air segments and the gravity potential of the air masses. The modelling shows a surface pressure-independent part of gravity variations induced by mass redistribution of the atmosphere in the order of some μgal. This part can only be determined by using 3D atmospheric pressure data. It has been calculated for the Vienna Superconducting Gravimeter site.From this follows that the gravity reduction can be improved by applying the 3D atmospheric attraction model for analysing long-periodic tidal waves including the polar tide. The same improvement is expected for reduction of long-term absolute gravity measurements or comparison of gravity measurements at different seasonal times. By using 3D atmospheric pressure data, the gravity correction can be improved up to some μgal.     

Application of the F-approximation to gravity data interpretation. II. The results of testing with the use of detailed gravity and magnetic surveys

The basic theoretical foundations of the spectral analysis of gravity and magnetic data based on the approximation approach have been considered and corresponding expressions implementing various statements of the F-approximation method have been derived [Strakhov and Kerimov, 1999; 2000; 2001]. The author considered the algorithms and computer implementation of the F-approximation of anomalous gravity and magnetic fields presented in the results of testing with the use of a number of model examples and data on the accuracy of the model field approximation earlier on in [Kerimov, 2003]. In this paper, I consider methodological features of constructing the F-approximation from the detailed gravity and magnetic surveys, anomalous gravity and magnetic fields reconstructed with the use of the F -approximation, and examples of the field transforms obtained with the use of this approach.     

Suitable gravity interpolation technique for large data gaps in Africa

Studia Geophysica et Geodaetica - The gravity database for the IAG African Geoid Project contains significantly large data gaps. These large data gaps affect the interpolation precision of the...