CRS-stack-based residual static correction

In the case of onshore data sets, the acquired reflection events can be strongly impaired due to rough top‐surface topography and inhomogeneities in the uppermost low‐velocity layer, the so‐called weathering layer. Without accounting for these influences, the poor data quality will make data processing very difficult. Usually, the correction for the top‐surface topography is not perfect. The residuals from this correction and the influence of the weathering layers lead to small distortions along the reflection events. We integrated a residual static correction method into our data‐driven common‐reflection‐surface‐stack‐based imaging workflow to further eliminate such distortions. The moveout‐corrected traces and the stacked pilot trace are cross‐correlated to determine a final estimate of the surface‐consistent residual statics in an iterative manner. As the handling of top‐surface topography within the common‐reflection‐surface stack is discussed in a separate paper in this special issue, the corresponding residual static correction will be explained in more detail. For this purpose, the results obtained with a data set from the Arabian Peninsula will be presented.     

Path-integral seismic imaging

A new type of seismic imaging, based on Feynman path integrals for waveform modelling, is capable of producing accurate subsurface images without any need for a reference velocity model. Instead of the usual optimization for traveltime curves with maximal signal semblance, a weighted summation over all representative curves avoids the need for velocity analysis, with its common difficulties of subjective and time‐consuming manual picking. The summation over all curves includes the stationary one that plays a preferential role in classical imaging schemes, but also multiple stationary curves when they exist. Moreover, the weighted summation over all curves also accounts for non‐uniqueness and uncertainty in the stacking/migration velocities. The path‐integral imaging can be applied to stacking to zero‐offset and to time and depth migration. In all these cases, a properly defined weighting function plays a vital role: to emphasize contributions from traveltime curves close to the optimal one and to suppress contributions from unrealistic curves. The path‐integral method is an authentic macromodel‐independent technique in the sense that there is strictly no parameter optimization or estimation involved. Development is still in its initial stage, and several conceptual and implementation issues are yet to be solved. However, application to synthetic and real data examples shows that it has the potential for becoming a fully automatic imaging technique.     

地震干涉技术被动源地震成像

被动源地震成像是基于地下反射波响应和透射波响应之间的关系,通过在地表接收由地下非人工震源发出的透射波响应,利用互相关运算来合成反射波响应的方法.合成的反射波响应,又称虚炮集记录等价于地表地震剖面记录.本文研究了由地下随机分布的被动源发出的透射波记录来合成虚炮集记录的基本原理,推导了反射波记录和透射波记录的关系公式;并通过数值模拟方法,分析了被动源成像的可行性.结果表明:利用被动源地震信息进行成像是可行的.     

利用背景噪声进行地震成像

利用长时序列背景地震噪声进行地震成像是最近的一项创新成果,它摆脱了传统方法须依赖地震获取地壳上地幔高分辨率信息的限制。新方法被称为背景噪声层析成像（ANT）,主要用于地震面波。随着背景噪声层析成像技术在最新部署的地震台阵（如美国台阵地球透镜项目）资料解释中的应用,更高分辨率的地壳上地幔地震模型已赫然显现。     

三维复杂山谷地形SV波垂直输入地震反应分析

本文基于显式有限元法研究了地震波垂直入射时三维复杂山谷地形对地震地面运动的影响,在数值分析中应用了三维化二维的解法和黏弹性人工边界的处理方法,实现了地震波垂直输入下三维复杂场地地震动数值模拟,并验证了该方法的合理性.以四川桃坪地区一山谷地形作为研究对象,基于地表高程数据分别建立了二维和三维场地模型,对比研究表明：在复杂地形情况下考虑二、三维模型时具有明显差异,三维模型能更真实地反映地形变化对地震动的影响,复杂地形条件下有必要考虑三维实际场地模型.本文对边界自由场的处理方法也可用于处理三维复杂场地地震动斜入射问题,为三维复杂地形场地地震效应研究提供参考.

     

Effect of topography and subsurface inhomogeneities on seismic SV waves

The effect of topography and subsurface inhomogeneity on surface motion is investigated in the case of incident SV waves. Several types of topography, such as a cliff, a cliff with a soft layer and filled land, are considered. Computations are made using a new method combining a particle model with a finite element method. The accuracy of this method is discussed through comparisons with Wong's solutions, which are in good agreement. It is found that the surface displacement is very much influenced by surface irregularities when the incident wavelengths are comparable to the size of the topographic features. Rayleigh waves are strongly produced in the neighbourhoods of the slopes of a cliff and a cliff with a soft layer, the latter being a cliff adjacent to and covered at its foot by a soft layer. Thus, a zone of large amplification takes place near a slope, combining incident SV waves and Rayleigh waves. A large displacement also occurs at the upper corner of the slope. In filled land, vertical and horizontal displacements are produced, which are 3 times larger than those at a distance. The present results are considered to be significant from the viewpoint of engineering seismology.     

Numerical evaluation of slope topography effects on seismic ground motion

This paper presents results of numerical analyses for the seismic response of step-like ground slopes in uniform visco-elastic soil, under vertically propagating SV seismic waves. The aim of the analyses is to explore the effects of slope geometry, predominant excitation frequency and duration, as well as of the dynamic soil properties on seismic ground motion in a parametric manner, and provide qualitative as well as quantitative insight to the phenomenon. Among the main conclusions of this study is that this kind of topography may lead to intense amplification or de-amplification variability at neighboring (within a few tens of meters) points behind the crest of the slope, especially for high frequency excitations. Nevertheless, a general trend of amplification near the crest and de-amplification near the toe of the slope seems to hold for the horizontal motion. As a result of these two findings, it becomes evident that reliable field evidence of slope topography aggravation is extremely difficult to establish. Furthermore, this study highlights the generation of a parasitic vertical component of motion in the vicinity of the slope, due to wave reflections at the slope surface, that under certain preconditions may become as large as the horizontal. Criteria are established for deciding on the importance of topography effects, while approximate relations are provided for the preliminary evaluation of the topographic aggravation of seismic ground motion and the width of the affected zone behind the crest.     

2D surface topography boundary conditions in seismic wave modelling

New formulations of boundary conditions at an arbitrary two-dimensional (2D) free-surface topography are derived. The top of a curved grid represents the free-surface topography while the grid's interior represents the physical medium. The velocity–stress version of the viscoelastic wave equations is assumed to be valid in this grid. However, the rectangular grid version attained by grid transformation is used to model wave propagation in this work in order to achieve the numerical discretization. We show the detailed solution of the particle velocities at the free surface resulting from discretizing the boundary conditions by second-order finite-differences (FDs). The resulting system of equations is spatially unconditionally stable. The FD order is gradually increased with depth up to eighth order inside the medium. Staggered grids are used in both space and time, and the second-order leap-frog and Crank–Nicholson methods are used for time-stepping. We simulate point sources at the surface of a homogeneous medium with a plane free surface containing a hill and a trench. Applying parameters representing exploration surveys, we present examples with a randomly realized surface topography generated by a 1D von Kármán function of order 1. Viscoelastic simulations are presented using this surface with a homogeneous medium and with a layered, randomized medium realization, all generating significant scattering.     

The effect of local irregular topography on seismic ground motion

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Effect of topography and subsurface inhomogeneity on seismic rayleigh waves

The effect of topography and subsurface inhomogeneity on surface motion is investigated in the case of Rayleigh waves. In the previous paper, the same effect was investigated in the case of SV waves. Several types of topography, such as cliffs both with and without a soft layer at the foot of the slope, are considered. Computations are made using a new hybrid method combining a particle model with a finite element method. In cases of harmonic Rayleigh waves, surface motions with amplitudes as large as 1.5 to 5 times the horizontal surface displacement of the incident Rayleigh waves are produced near the slope and the sloping interface. When a Rayleigh wave propagating through a hard single-layered ground encounters a sloping interface where hard ground and soft ground make contact with each other, Rayleigh waves having two different, phase velocities are produced and they correspond to the fundamental mode, and the first mode determined by Haskell's method. In addition, the transient response when Rayleigh waves propagate through the cliff is also simulated. Assuming the vertical component of the Tokachi-oki Earthquake (1968) measured on the surface to be a Rayleigh wave, the incident Rayleigh wave can be obtained by a Fourier synthesis of eigenfunctions of Rayleigh waves.     

模型扩展和地形平化起伏地形处理方案在地震走时层析成像中的对比研究

中国大陆中西部普遍具有强烈的地形起伏,起伏地形会对地震资料的处理分析产生严重干扰.精细处理起伏地形成为高精度地震成像的必然要求.传统方法通过填充低速介质将不规则模型扩展为规则模型来处理起伏地形.近年来,借助坐标变换将物理空间不规则模型转换为计算空间规则模型的地形平化方法,为解决起伏地形问题提供了新思路.本文基于经典的模型扩展和新发展的地形平化方法分别处理起伏地形,从走时正演、射线追踪和反演成像三个方面,全面细致地评判了两种地形处理方法在起伏地形层析成像中的适用性和有效性.结果表明,模型扩展中阶梯状近似和填充介质速度参与计算,会造成起伏地形走时计算精度损失,出现虚假射线路径和错误出射角,导致反演分辨率降低,成像结果模糊甚至失真;地形平化中采用贴体网格参数化,能够保证离散模型完全匹配起伏地形,并且保持起伏地形在物理空间和计算空间中均为自由表面.在此基础上发展的层析成像技术具有高度的保真性,有效地处理了地形起伏效应,为起伏地形区域精细速度成像提供了有力的技术保障.

     

A macro-level global seismic damage model considering higher modes

For modal pushover analysis procedures, the model proposed by Ghobarah et al. (called the G model hereafter, 1999) has been extended to account for the contributions of transient higher modes to global seismic damage of structures excited by strong ground motions. The proposed model has physically and perfectly bridged the G model and the final softening model proposed by DiPasquale and Cakmak (1988). Modal damage indexes corresponding to all considered vibration modes are combined by the CQC rule or the SRSS rule. Incremental dynamic analysis (IDA) is performed on three example RC frames to validate the proposed model, and a comprehensive comparison is carried out. The demonstration indicates that the proposed model is easy to implement and reflects the influence of the transition in transient vibration periods and modes on structural damage evolution. Some limitations associated with the proposed model are also addressed. Further experimental validations are needed to improve the model in the future.     

Transverse seismic response of beam aqueduct considering fluid-structure coupling

Based on the theory of Housner, the transverse seismic response of beam aqueduct considering fluid-structure cou-pling is established. With the variation of aqueduct cross-section ratio of depth to width, the aqueduct transverse seismic response change. The transverse seismic response of a large-scale aqueduct in several work condition are calculated. It shows that the transverse seismic response is greatly influenced by the water mass in the aqueduct, but the shaking water play a TLD role. If the whole water is appended aqueduct body, it will magnify seismic iner-tia action. When aqueduct cross-section is selected, the influence of ratio of depth and width to pier seismic re-sponse should be considered in order to reduce seismic action.     

土与结构相互作用对储罐地震响应的影响

为了研究土与结构相互作用对储罐地震响应的影响,基于Haroun-Housner模型,将地基土考虑为平动和转动的弹簧阻尼体系,将储罐结构体系简化为三质点四自由度力学模型,来研究储罐的地震响应受地基土弹性的影响。分析结果表明:与刚性基础相比,考虑土与结构的相互作用时储罐的基底剪力、倾覆力矩和晃动波高均有放大效应,且与储液高度与半径比相关,为获得理想的地震响应储液高度与半径比存在优化取值区间。     

带地形高频大地电磁法有限元数值模拟

随着中深度地球物理勘探的迫切需要,以美国EH-4电导率成像系统为代表的高频大地电磁法在我国地球物理勘探行业应用越来越广泛,其勘探深度在地下1000 m以浅,频率范围10 Hz～100 KHz.本文研究了带地形的高频率大地电磁法有限元高精度、快速数值模拟.首先利用广义变分原理推导出电磁场的有限元方程,编制了双线性和双二次插值有限元程序,对典型山谷和山脊地形的数值模拟结果进行了分析,得出了一些有意义的结论.     

利用背景噪声进行地震成像的新方法

利用背景地震噪声提取格林函数，即通过一对台站记录的地震噪声进行互相关计算，来近似台站间的格林函数，并进一步通过地震成像获取地下结构的认识，成为最近跨学科研究的热点问题之一.本文首先叙述了其发展背景及过程，然后分别从四个角度，简要介绍了目前对其物理原理的解释.如果该方法能得到进一步的发展，将不再依赖于天然地震以及人工地震，而仅仅利用地震台站记录的地震噪声便可获取高分辨率的地下成像.该方法将会大大促进地震学的发展.     

Multi-criteria decision making for seismic intensity measure selection considering uncertainty

Seismic intensity measure (IM) selection is associated with consideration of multiple criteria, and there are uncertainties within the selection process. In this paper, a novel multi-criteria decision making (MCDM) approach by incorporating stochastic multi-criteria acceptability analysis (SMAA) with technique for order preference by similarity to ideal solution (TOPSIS) is proposed to solve the stochastic decision making problem of IM selection. TOPSIS provides an alternative rank function, and the SMAA is used to address the uncertainties within the IM selection. The performance criteria (e.g., efficiency, proficiency, practicality, sufficiency, and correlation) are evaluated for the investigated structural components, and the decision matrix is formulated based on the criteria of each IM alternative. Furthermore, the importance of the component to system reliability is quantified in a probabilistic manner using nonlinear time history analysis and serves as the weighting factors in MCDM stage. The holistic acceptability indices indicating the overall acceptability levels of IM alternatives are computed by the proposed approach. Additionally, the effects of different IMs (e.g., average spectral acceleration, peak ground velocity, and spectral acceleration) on probabilistic seismic loss and resilience are investigated to further support the IM selection. The proposed approach is illustrated on a highway bridge, and the results are presented.     

Unification of single-configuration seismic imaging processes

In this paper we derive an integral formula that encompasses all linear processes on seismic data. These include migration, demigration and residual migration, as well as data mapping procedures such as transformation to zero offset, inverse transformation to zero offset, residual transformation to zero offset and offset continuation. The derivation of the equation is different from all previous approaches to unification. Here we do not use a cascaded operation between two operators, but rather the superposition principle. In this regard, the derivation is not only more fundamental, but also simpler and more general. We study the kinematics and the dynamics of these processes and show that the signals can be reconstructed asymptotically either by finding the envelope of particular surfaces or by stacking energy along “adjoint” surfaces. For example, in the case of migration, the first set of surfaces are isochrons, while the “adjoint” surfaces are diffraction responses. In practice, the distinction between these two types of surfaces is equivalent to choosing the order of the computational loops with regard to the input and output seismic traces.     

考虑地震动持时效应的输电塔-线体系响应研究

研究了地震动持时效应对输电塔-线体系动力响应的影响。基于能量持时的定义方法,选取了一组包括20条长持时和20条短持时的地震动作为输入。地震动调幅至0.2g和1.2g来分别研究地震动持时效应对结构弹性和塑性响应的影响,并选取输电塔的塔顶峰值加速度、位移、主材应力以及节间位移角作为评价指标。结果表明:地震动持时效应对所选取的评价指标具有不同的影响规律,在输电塔-线体系动力响应研究中持时效应不容忽视。可以为输电塔的抗震设计提供有益的参考。     

Crooked line, rough topography: advancing towards the correct seismic image

Seismic exploration in mountainous areas imposes serious compromises on both acquisition and processing. Access restrictions usually result in profiles that are not straight and are not recorded along the true dip direction (if there is a true dip direction!). Processing constraints often result in very poor approximate corrections for elevations and for deviations from a straight line. Most fundamentally, 2D acquisition and processing assumes that the earth is 2D; this assumption is often seriously violated in mountainous areas. While we cannot efficiently correct 2D seismic data for the effects of a fully 3D subsurface, we can improve the data quality in thrust areas where the assumption of 2D subsurface variation is reasonable. We do this in a series of small steps, which improves the accuracy of several approximations made in processing 2D land data.