An Adaptive Wavenumber Sampling Strategy for 2.5D Seismic-Wave Modeling in the Frequency Domain

Simulation of seismic waves from a 3D point-source in a 2D medium may be performed in the frequency-wavenumber domain (called 2.5D modelling). It involves computing the Fourier-transformed Green's function for a number of frequency (ω) and strike direction wavenumber (k_y) values and doubly inverse transforming to convert to the traveltime and distance space. Such modeling produces a wavefield with 3D features but the computation becomes pseudo 2D (i.e., in the xz-plane) rather than 3D (in the xyz-frame). The common sampling strategy for the wavenumber is inefficient for 2.5D wave modeling because it employs a large number of wavenumbers (k_y). This leads to a high cost of computer time in the linear-equation-solving processing, which detracts from the advantages of 2.5D modeling. In this paper, we use two analytic frequency-wavenumber-domain solutions for seismic waves in a homogeneous medium and an inhomogeneous media (two semi-infinite media in contact) to investigate the properties of the solutions and an efficient sampling strategy for choosing the wavenumbers. We have carried out analytic and numerical experiments with these solutions, and present adaptive Gauss–Legendre abscissae for the wavenumber sampling in terms of a modeling situation. We show that the effective range and the number of sampling points of the wavenumber define the adaptive sampling strategy, and they can be estimated in terms of the wavelength and the maximum source-receiver offset. We apply this sampling strategy to the finite-element method and demonstrate that the range and number of sampling points may be adapted for obtaining significant computational efficiency and satisfactory accuracy for every frequency component. Such 2.5D wave modeling can be readily applied for frequency-domain full-waveform inversion for seismic surface measurements and crosshole seismic waveform tomography.     

震害预测中抽样方法的研究

本文阐述了在震害预测中采用分块抽样方法的一般原理,对于确定抽样样本总额的方法和样本总额在分块抽样中的理想分配进行了讨论,文中以乌鲁木齐市钢筋混凝土房屋的震害预测为对象,说明了分块抽样法的实际应用及其对于随机抽样法的优越性。文中对逐栋调查和分块抽样调查所得到的震害预测结果进行了对比,论述了这一抽样方法的可行性。     

Seismic analysis of underground tunnels by the 2.5D finite/infinite element approach

A procedure for the seismic analysis of underground tunnels using recorded free-field earthquakes based on the 2.5D finite/infinite element approach is presented. The near and far fields of the half space are modeled by finite and infinite elements, respectively. Using the 1D wave theory, the nodal force and displacement on the near-field boundary are computed for each spectral frequency of the earthquake. Then, equivalent seismic forces are computed for the near-field boundary for the earthquake spectrum. By assuming the soil-tunnel system to be uniform along the tunnel axis, the 2.5D approach can account for the wave transmission along the tunnel axis, which reduces to the 2D case for infinite transmission velocity. The horizontal and vertical components of the 1999 Chi-Chi Earthquake (TCU068) are adopted as the free-field motions in the numerical analysis. The maximal stresses and distribution patterns of the tunnel section under the P- and SV-waves are thoroughly studied by the 2.5D and 2D approaches, which should prove useful to the design of underground tunnels.     

CPU/GPU协同计算在频率域二维全波形反演中的应用

全波形反演利用波场的运动学和动力学信息重建地下物理参数,是建立高精度速度模型的有效手段,巨大的计算量是制约其实用化的瓶颈之一。本文针对全波形反演中频率域正演的复杂计算问题,采用粗细结合的并行策略,将MPI技术应用于多炮间并行计算,同时利用GPU技术加速正演过程中大型稀疏线性代数方程组的求解,以提高频率域全波形反演的计算效率。通过理论模型验证本文方法的正确性和有效性,给出不同数据量与GPU计算效率的相关分析结论,提出频率域全波形反演CPU/GPU协同并行计算的制约瓶颈和发展方向。     

Modelling Seismic Waves Around Underground Openings in Fractured Rock

—?The potential for large excavation-induced seismic events may be recognised, even if the timing of an event may be inherently unpredictable. In this case, modelling the wave propagation from a potential event could allow the dynamic motions around an excavation to be projected, and for areas of danger to be anticipated. However, the above and other potential applications require accurate models of wave interaction with the openings, as well as with the fractured rock which surrounds such excavations. This paper considers real recorded waveforms and how well these waveforms are modelled by explicit mechanical models of the source, the medium and the excavation. Models of experiments at three different scales of the problem are presented: small and large amplitude waveforms recorded around a deep-level mining tunnel in a synthetic rockburst experiment; waveforms from laboratory experiments of waves through plates of steel representing fractures; waveforms from active pulses in an acoustic emission experiment in a small volume of fractured rock at the surface of an underground excavation. The results show that elastic wave propagation around an excavation was a first approximation for small amplitude waves, but was less successful for modelling large amplitude waves and more fractured rock. Fractures in the models were represented explicitly with displacement discontinuities. Waveforms through known fracture geometries were particularly well-reproduced, and indicate the importance of fracture stiffness, the in situ stress state, and stress-dependence of the fractures in such models. Overall, the models are sufficiently successful at representing recorded behaviour, to be encouraging for the goal of representing accurate wave motions around excavations.     

Modelling of Seismic Ground Motion in Santiago de Cuba City from Earthquakes in Oriente Fault Seismic Zone

— We present the results of complete P-SV and SH waves modelling, up to a maximum frequency of 1?Hz, along two profiles in Santiago de Cuba city. The seismic sources are located in the depth range from 10 to 40?km on the Oriente fault zone at distances of several tens of kilometres from the city. The calculation has been made by a hybrid method: Modal summation in the regional anelastic model (one-dimensional) where the source is buried, and finite differences in the local sedimentary anelastic models (two-dimensional). The analysis of the influence of the depth and of the distance of the source on the site effects shows that standard traditional methods, based on the deconvolution analysis of the rock outcrop motion, can lead to erroneous results.     

Modelling Seismic Hazard in Earthquake Loss Models with Spatially Distributed Exposure

The prediction of possible future losses from earthquakes, which in many cases affect structures that are spatially distributed over a wide area, is of importance to national authorities, local governments, and the insurance and reinsurance industries. Generally, it is necessary to estimate the effects of many, or even all, potential earthquake scenarios that could impact upon these urban areas. In such cases, the purpose of the loss calculations is to estimate the annual frequency of exceedance (or the return period) of different levels of loss due to earthquakes: so-called loss exceedance curves. An attractive option for generating loss exceedance curves is to perform independent probabilistic seismic hazard assessment calculations at several locations simultaneously and to combine the losses at each site for each annual frequency of exceedance. An alternative method involves the use of multiple earthquake scenarios to generate ground motions at all sites of interest, defined through Monte–Carlo simulations based on the seismicity model. The latter procedure is conceptually sounder but considerably more time-consuming. Both procedures are applied to a case study loss model and the loss exceedance curves and average annual losses are compared to ascertain the influence of using a more theoretically robust, though computationally intensive, procedure to represent the seismic hazard in loss modelling.An erratum to this article can be found at     

台站地震资料的时频域自适应极化分析和滤波

提出一种自适应协方差的时频域极化滤波方法。该方法在广义S变换时频方法的基础上,构造时频域自适应协方差矩阵,通过特征分析计算时频域瞬时极化参数,设计极化滤波器,实现多分量地震极化分析和滤波。其优势在于协方差矩阵的分析时窗的长度由多分量地震数据的瞬时频率确定,可以自适应于有效信号的周期,在每个时频点计算极化参数不需要进行插值处理;结合时间频率信息,解决在时间域或频率域波形或频率重叠的信号具有明显的直观性。模型数据及实际三分量台站地震数据处理结果表明,该极化滤波方法在台站地震资料分析和处理方面具有很好的直观性和较高的分辨率。     

曲波域不规则地震数据提高分辨率技术研究

受野外观测条件的限制,采集的地震数据体通常不规则,并缺失一部分数据道。传统的单道提高分辨率方法无法兼顾横向地震信息,处理结果存在空间一致性问题。为此,本文提出在曲波域内进行不规则地震数据,通过曲波变换实现对地震数据的稀疏表征,将提高分辨率问题转化为曲波域1-范数约束的稀疏促进求解,得到规则化的高分辨率地震数据体。该方法避免传统单道提高分辨率方法存在的局限性,在提高分辨率的同时,能够恢复缺失的地震数据、压制随机噪声,进而提高地震数据的完备性,模型和实际资料试算,验证了该方法的正确性、有效性和适用性。     

一种基于频域外推的不完全角度CT重建算法

不完全角度重建问题一直是CT图像重建领域研究的重点和难点。目前,通常的不完全角度重建方法是基于空域的迭代方法,但由于正反投影的高计算复杂度,空域迭代方法存在计算耗时,对硬件资源需求大等问题。本文提出了一种基于外推的邻近网格迭代算法(INNG-TV)。首先,平行束采样的数据通过傅里叶变换和样条插值到频域空间,然后在迭代的过程中,傅立叶空间投影已知部分的数据始终不变,缺失部分数据通过对重建图像进行INNG外推得到,同时在图像空间对重建图像做非负、最小化总变分等先验及优化约束。     

频率域波动方程的双参数识别方法

利用反射波地震记录恢复波动方程的两个系数以研究地球内部构造，是当前应用地球物理研究的热点之一，本文在波动方程反演方法的理论基础上，导出了频率域识别介质的密度波速两个重要参数的新算法，从而把当前的波动方程单参数反演双参数反演方法，通过理论模型及实际测井资料的反演试算对比，均藜得良好效果，在算法中还省去了Ｇｒｅｅｎ函数的繁杂计算，节省了计算量，增加实用性。     

Review of Ray Theory Applications in Modelling and Imaging of Seismic Data

Throughout the last twenty years, 3D seismic ray modelling has developed from a research tool to a more operational tool that has gained growing interest in the petroleum industry. Various areas of application have been established and new ones are under development. Many of these applications require a modelling system with flexible, robust and efficient modelling algorithms in the core. The present paper reviews the basic elements of such a system, based on the open model concept and the wavefront construction technique. In the latter, ervený's dynamic ray tracing is an intrinsic part. The modelling system can be used for generating ray attributes and synthetic seismograms for realistic 3D surveys with tens of thousands of shots and receivers. Moreover, some other types of application areas are illustrated: Production of Green's functions for prestack depth migration and hybrid modelling (combined ray and finite-difference modelling), attribute mapping and illumination analysis, both for survey planning and interpretation. Finally, the concepts of isochron rays and velocity rays related to seismic isochrons have been introduced recently, with very interesting future applications.     

2.5维非均匀介质中的地震波数值模拟

目前,完全的3D弹性波数值模拟计算仍然需要庞大的计算资源,而2D弹性波数值模拟,又不能准确地近似3D数值模拟.因此,本文在较高数值精度的一阶应力一速度弹性波动方程的基础上,采用时间错格差分拟谱方法在2D模型介质中计算3D弹性波场,即2.5D数值模拟.并将3D计算结果与2.5D和2D结果进行比较,发现2.5D模拟结果在波场形态和振幅方面比2D模拟结果更接近3D模拟结果,从而证实了2.5D数值模拟比2D数值模拟可以更好地近似3D波场数值模拟,同时证实了时间错格差分拟谱方法是一种高精度、高效率的正演模拟方法.     

城市轨道交通高架桥梁抗震设计中的关键问题

伴随我国城市轨道交通建设的快速发展,轨道交通抗震安全已成为我国大中型城市和地区生命安全、交通秩序、正常的经济和社会活动的重要保障。本文针对城市轨道交通高架桥梁结构和线路运行特点,结合国内外地震中铁路和轨道交通桥梁破坏特征,参照桥梁抗震设计思想和国内外桥梁抗震设计规范内容,综合论述了轨道交通抗震设计中抗震设防分类、设防标准与性能目标的确定,结构安全和行车安全指标的选取,桩-土相互作用、轨道系统和车辆作用的模拟等关键问题,并结合设计工作特点,对研究工作与设计工作的结合提出了建议。     

中国海域地震区划及关键问题研究

国家重点研发计划项目《海域地震区划关键技术研究》已实施3年,进入项目结题阶段,已形成海域地震区划方法与技术体系,研究成果为即将开展的中国海域地震区划图编制工作提供技术支撑.项目组分析和探讨了海域地震区划研究基础与存在的问题,结合所关注的关键科学和技术问题,介绍和分析了主要研究成果和进展,包括海域断裂活动性探测和地震构造...     

Computing the Sensitivity Kernels for 2.5-D Seismic Waveform Inversion in Heterogeneous,Anisotropic Media

2.5-D modeling and inversion techniques are much closer to reality than the simple and traditional 2-D seismic wave modeling and inversion. The sensitivity kernels required in full waveform seismic tomographic inversion are the Fréchet derivatives of the displacement vector with respect to the independent anisotropic model parameters of the subsurface. They give the sensitivity of the seismograms to changes in the model parameters. This paper applies two methods, called ‘the perturbation method’ and ‘the matrix method’, to derive the sensitivity kernels for 2.5-D seismic waveform inversion. We show that the two methods yield the same explicit expressions for the Fréchet derivatives using a constant-block model parameterization, and are available for both the line-source (2-D) and the point-source (2.5-D) cases. The method involves two Green’s function vectors and their gradients, as well as the derivatives of the elastic modulus tensor with respect to the independent model parameters. The two Green’s function vectors are the responses of the displacement vector to the two directed unit vectors located at the source and geophone positions, respectively; they can be generally obtained by numerical methods. The gradients of the Green’s function vectors may be approximated in the same manner as the differential computations in the forward modeling. The derivatives of the elastic modulus tensor with respect to the independent model parameters can be obtained analytically, dependent on the class of medium anisotropy. Explicit expressions are given for two special cases—isotropic and tilted transversely isotropic (TTI) media. Numerical examples are given for the latter case, which involves five independent elastic moduli (or Thomsen parameters) plus one angle defining the symmetry axis.     

多分量地震记录P和SV波场的τ-p域分离方法

多分量地震观测记录到来自地下介质的全波场,利用分离的P和SV波场联合反演可以提供地下介质岩性、孔隙度、孔隙流体、裂隙和各向异性的重要信息.     

南海岛礁场地地震稳定性研究中的关键问题探讨

目前我国针对陆域地区的建筑物和构筑物已建立了比较完备的抗震设计理论和技术体系,但对于海洋工程的抗震研究工作开展得不充分,尤其是海洋岛礁场地的地震反应分析尚属空白。伴随着近年来我国南海地区的迅速开发建设,有必要对南海岛礁的地震危险性分析和抗震设计展开研究。介绍南海岛礁场地的特殊工程地质条件和地震活动性特征,通过比较目前国内外常用的场地地震反应分析方法,针对岛礁这一特殊工程地质体,提出岛礁场地地震反应分析中需要考虑的四个显著因素,包括(1)南海岛礁体的特殊地形;(2)南海岛礁特殊的岩土工程材料;(3)海水-岛礁体动力相互作用;(4)南海地区海底输入地震动的确定,并探讨解决这些问题的思路。为分析地震作用下岛礁场地的稳定性、场地反应分析提供研究思路,同时为南海岛礁建设中的地震危险性分析提供参考。