共查询到20条相似文献，搜索用时 140 毫秒
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It seems that electromagnetic tomography is quite suitable to be used in metal and groundwaterexploration. especial for limestone areas where the absorption coefficient of electromagnetic wave is smalland geological body has a large property contrast with country rock it should be pointed out that there exitsome uncertainties in geological interpretation of EM tomogram, corresponding laboratory tests for rockphysical property are always necessary.Resistivity tomography provides us a new useful… 相似文献
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In this paper, we present a new method for seismic stratigraphic absorption compensation based on the adaptive molecular decomposition.
Using this method, we can remove most of the effects resulting from wavelets truncation and interference which usually exist
in the common time-frequency absorption compensation method. Based on the assumption that the amplitude spectrum of the source
wavelet is smooth, we first construct a set of adaptive Gabor frames based on the time-variant properties of the seismic signal
to transform the signal into the time-frequency domain and then extract the slowly varying component (the wavelet’s time-varying
amplitude spectrum) in each window in the time-frequency domain. Then we invert the absorption compensation filter parameters
with an objective function defined using the correlation coefficients in each window to get the corresponding compensation
filters. Finally, we use these filters to compensate the time-frequency spectrum in each window and then transform the time-frequency
spectrum to the time domain to obtain the absorption-compensated signal. By using adaptive molecular decomposition, this method
can adapt to isolated and overlapped seismic signals from the complex layers in the inhomogeneous viscoelastic medium. The
viability of the method is verified by synthetic and real data sets. 相似文献
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Quantitative imaging of complex structures from dense wide-aperture seismic data by multiscale traveltime and waveform inversions: a case study 总被引：3，自引：0，他引：3
S. Operto C. Ravaut L. Improta J. Virieux A. Herrero P. Dell'Aversana 《Geophysical Prospecting》2004,52(6):625-651
An integrated multiscale seismic imaging flow is applied to dense onshore wide‐aperture seismic data recorded in a complex geological setting (thrust belt). An initial P‐wave velocity macromodel is first developed by first‐arrival traveltime tomography. This model is used as an initial guess for subsequent full‐waveform tomography, which leads to greatly improved spatial resolution of the P‐wave velocity model. However, the application of full‐waveform tomography to the high‐frequency part of the source bandwidth is difficult, due to the non‐linearity of this kind of method. Moreover, it is computationally expensive at high frequencies since a finite‐difference method is used to model the wave propagation. Hence, full‐waveform tomography was complemented by asymptotic prestack depth migration to process the full‐source bandwidth and develop a sharp image of the short wavelengths. The final traveltime tomography model and two smoothed versions of the final full‐waveform tomography model were used as a macromodel for the prestack depth migration. In this study, wide‐aperture multifold seismic data are used. After specific preprocessing of the data, 16 frequency components ranging from 5.4 Hz to 20 Hz were inverted in cascade by the full‐waveform tomography algorithm. The full‐waveform tomography successfully imaged SW‐dipping structures previously identified as high‐resistivity bodies. The relevance of the full‐waveform tomography models is demonstrated locally by comparison with a coincident vertical seismic profiling (VSP) log available on the profile. The prestack depth‐migrated images, inferred from the traveltime, and the smoothed full‐waveform tomography macromodels are shown to be, on the whole, consistent with the final full‐waveform tomography model. A more detailed analysis, based on common‐image gather computations, and local comparison with the VSP log revealed that the most accurate migrated sections are those obtained from the full‐waveform tomography macromodels. A resolution analysis suggests that the asymptotic prestack depth migration successfully migrated the wide‐aperture components of the data, allowing medium wavelengths in addition to the short wavelengths of the structure to be imaged. The processing flow that we applied to dense wide‐aperture seismic data is shown to provide a promising approach, complementary to more classical seismic reflection data processing, to quantitative imaging of complex geological structures. 相似文献
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为了避免使用不合理初始辐射场强和方向性因子带来的误差,研究了估计辐射参数的井间电磁波层析成像技术.通过时域有限差分法模拟表明,天线长度与波长的比值、钻孔充填情况、钻孔周围介质的物性均会影响偶极天线的初始辐射场强或方向性因子;为此结合已知的分层资料,将它们设为未知参数,并设定初始辐射场强与发射点位置相关,方向性因子随射线角度而变化;采用正则化反演方法,由钻孔资料建立了模型方差目标函数,使得反演结果与钻遇的地质特征保持一致.通过理论模型试验和实例应用分析表明,相对于传统射线层析成像方法,估计辐射参数的正则化层析成像技术有助于提高反演的准确性. 相似文献
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场地条件对地震动幅值和频谱特性均有影响, 现行的中国地震动参数区划图根据场地类别调整地震动反应谱特征周期, 但尚未考虑到对地震动峰值和反应谱平台值的调整. 以成都盆地为例, 广泛收集了盆地范围内的工程钻孔资料. 考虑到不同工程地质分区内场地地震动参数可能存在较大差异, 在研究区工程地质分区的基础上, 利用等效线性化方法对钻孔进行了土层地震反应分析, 给出了成都盆地内不同工程地质分区的地震动参数调整系数建议值. 相似文献
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Po Chen 《Pure and Applied Geophysics》2011,168(10):1527-1552
The seismological inverse problem has much in common with the data assimilation problem found in meteorology and oceanography. Using the data assimilation methodology, I will formulate the seismological inverse problem for estimating seismic source and Earth structure parameters in the form of weak-constraint generalized inverse, in which the seismic wave equation and the associated initial and boundary conditions are allowed to contain errors. The resulting Euler?CLagrange equations are closely related to the adjoint method and the scattering-integral method, which have been successfully applied in full-3D, full-wave seismic tomography and earthquake source parameter inversions. I will review some recent applications of the full-wave methodology in seismic tomography and seismic source parameter inversions and discuss some challenging issues related to the computational implementation and the effective exploitation of seismic waveform data. 相似文献
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面向海域工程抗震设计及评估对海底地震动的需求,基于日本相模湾海域K-NET的ETMC海底强震动记录,根据震级、震中距选取面向工程输入的949组地震动记录数据库。在考虑震源类型差异的基础上,对地震动峰值、持时、频谱等参数进行分析,通过反应谱、Arias烈度等指标描述典型海底地震动特征。根据峰值加速度、显著持时等强度指标对海底地震动记录进行排序,给出基于不同地震动特征分类下的典型地震动记录。推荐的海底地震动可为考虑不同结构需求参数的典型海域工程结构时程分析提供输入地震动。 相似文献
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应用地震波速CT和吸收CT相结合的方法对山东省招远市界河金矿隐伏采空区进行了联合探测研究．波速CT是利用地震波走时资料反演地质体内部波速结构;吸收CT是通过能量变化观测反演吸收系数分布．地震波速对岩性敏感,吸收系数与岩石的完整性关系更密切在界河金矿采空区探测中利用地震波速和吸收系数为层析物理量,在巷道和地表间进行透射观测,以优于2m的分辨率清楚地揭示了测区内采空区和断裂破碎带的分布,探测结果已被后期的采掘所证实．探测的成功为解决同类问题提供了一种可行的方案,对促进工程地球物理探测技术的发展也有重要意义． 相似文献
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工程场地地震安评中加速度反应谱标准化问题的讨论 总被引：1，自引：1，他引：0
文中计算了不同地震输入模式下的拱桥地震反应,讨论了输入指定地震波进行时域计算结果和按对应的反应谱进行计算所得结果之间的差异,特别分析了分别按地震波的实际反应谱和经过标定的反应谱计算得到的拱桥地震反应之间的不同.数值结果表明:在工程场地地震安全性评价中,采用标准反应谱的方式所提供的场地地震加速度参数,将会抹杀土层场地动力特性对地表地震动的影响.因此,按此地震动参数进行结构反应计算时,有时会低估结构的地震反应,留下结构抗震不安全的隐患. 相似文献
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垂直地震剖面（Vertical Seismic Profile,简称VSP）和层析成像（Computerized Tomography,简称CT）方法,不仅能够使用统一的数学方法描述（如射线理论）,并且在其勘探实践活动中完全可融为一体而成为优化技术组合下的高分辨工程物探方法.特别是在井间地震CT数据采集现场施工中,充分利用VSP和井间CT数据采集方式的兼容性和优化观测系统参数设计,几乎可以不增加野外工作费用,就能够同时获取井间地震CT数据和施测孔的逆向VSP数据体.如井中排列多点激发,地面各接收点构成多偏移距逆向VSP道集,并可组成关于孔中各炮点的变偏移距逆向VSP道集.这种高分辨技术组合在近地表大中型岩土洞室工程测试环境中更易于实现.本文简述了工程VSP与地震CT数据一体化观测系统,介绍了联合速度反演初始模型的建立与成像处理流程,给出VSP和CT联合成像方法应用于三峡大坝工程物探检测中的一个实例简介,最后得出相关结论并提出建议. 相似文献
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Prony filtering is a method of seismic data processing which can be used to solve various geological and production tasks, involving an analysis of target horizons characteristics and a prediction of possible productive zones. This method is based on decomposing the observed seismic signals by exponentially damped cosines at short-time intervals. As a result, a discrete Prony spectrum including values of four parameters (amplitude, damping factor, frequency, phase) can be created. This decomposition occurs at many short-time intervals moving along an observed trace. The combined Prony spectrum of the trace can be used to create images of the trace through a selection of some values of the parameters. These images created for all traces of a seismic section provide an opportunity for locating zones of frequency-dependent anomalous scattering and absorption of seismic energy. Subsequently, the zones can be correlated with target seismic horizons. Analysis and interpretation of these zones may promote understanding of the target horizons features and help to connect these features with the presence of possible reservoirs. 相似文献
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In seismic tomography the observed traveltimes or amplitudes of direct waves are inverted to obtain an estimate of seismic velocity or absorption of the section surveyed. There has been much recent interest in using cross-well traveltime tomography to observe the progress of fluids injected into the reservoir rocks during enhanced oil recovery (EOR) processes. If repeated surveys are carried out, then EOR processes may be monitored over a period of time. This paper describes the results of a simulated time-lapse tomography experiment to image the flood zone in an EOR process. Two physical models were made out of epoxy resins to simulate an essentially plane-layered sedimentary sequence containing a reservoir layer and simple geological structure. The models differed only in the reservoir layer, which was uniform in the ‘pre-flood’ model and contained a flood zone of known geometry in the ‘post-flood’ model. Data sets were acquired from each model using a cross-well survey geometry. Traveltime and amplitude tomographic imaging techniques have been applied to these data in an attempt to locate the extent of the flood zone. Traveltime tomography locates the flood zone quite accurately. Amplitude tomography shows the flood zone as a region of higher absorption, but does not image its boundaries as precisely. This is primarily because of multipathing and diffraction effects, which are not accounted for by the ray-based techniques for inverting seismic amplitudes. Nevertheless, absorption tomograms could complement velocity tomograms in real, heterogeneous reservoirs because absorption and velocity respond differently to changes in liquid/gas saturations for reservoir rocks. 相似文献
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Attenuation of random noise and enhancement of structural continuity can significantly improve the quality of seismic interpretation. We present a new technique, which aims at reducing random noise while protecting structural information. The technique is based on combining structure prediction with either similarity‐mean filtering or lower‐upper‐middle filtering. We use structure prediction to form a structural prediction of seismic traces from neighbouring traces. We apply a non‐linear similarity‐mean filter or an lower‐upper‐middle filter to select best samples from different predictions. In comparison with other common filters, such as mean or median, the additional parameters of the non‐linear filters allow us to better control the balance between eliminating random noise and protecting structural information. Numerical tests using synthetic and field data show the effectiveness of the proposed structure‐enhancing filters. 相似文献
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Source side seismic tomography(3STomo):A novelmethod to image the subsurface structure beneath seismically active region 
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下载免费PDF全文 We propose a novel seismic tomography method,Source Side Seismic Tomography(3STomo),which is designed particularly to image the subsurface structure beneath seismically active regions.Unlike the teleseismic tomography,in which the data are relative traveltime residuals between closely spaced stations for each teleseismic event,3STomo uses relative traveltime shifts between earthquakes within the study region for each distant station.Given the relatively evener distribution of global seismic stations,this method has unique advantages for imaging the structure beneath regions that have numerous earthquakes but lack of dense seismic stations,for example,some subduction zones and spreading ridges in the ocean.In addition,3STomo has potentially better vertical resolution at shallow depths than the traditional teleseismic tomography.The effect of the inaccurate source parameters on its resolution can be minimized by using depth phases and the technique of joint source and structure inversion.Numerical experiments and application to Luzon Island,Philippines show that 3STomo can be a valuable tool to investigate the subsurface structure beneath some areas where the traditional method cannot be applied to,or at least it can be used as a complementary component of conventional teleseismic tomography to obtain better back-azimuth coverage and achieve higher resolution at shallow depths in the inversion. 相似文献
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Crosshole ultrasonic tomography is referred to ray tracing by gilding method and image reconstruction by combining the successively linearized iteration with damping least-squares QR decomposition, with which the result has better precision than that with crosshole seismic tomography by using the same inversion method in engineering geological investigation. It has been proved in practice that the investigation with crosshole ultrasonic tomography can clearly show the location and shape of the abnormal geological unit with the volume more than 60 cm when the crosshole distance exceeds 30 m. The result of investigation has been confirmed by the drilling. The crosshole ultrasonic tomography method will be extensively used in the engineering geological investigation. 相似文献