Asymptotic Ray Theory for Seismic Surface Waves in Laterally Inhomogeneous Media

A recurrence procedure is outlined for constructing asymptotic series for surface wave field in a half-space with weak lateral heterogeneity. Both horizontal variations of the elastic parameters and of the wave field are assumed small on the distances comparable with the wavelength. This is equivalent to the condition that the frequency is large. The Surface Wave Asymptotic Ray Theory (SWART) is an analog of the asymptotic ray theory (ART) for body waves. However the case of surface waves presents additional difficulty: the rate of amplitude variation is different in vertical and horizontal directions. In vertical direction it is proportional to the large parameter . To overcome this difficulty the transformation equalizing vertical and horizontal coordinated is suggested, Z = z. In the coordinates x,y,Z the wave field is represented as an asymptotic series in inverse powers of . The amplitudes of successive terms of the series are determined from a recurrent system of equations. Attention is paid to similarity and difference of the procedures for constructing the ray series in SWART and ART. Applications of SWART to interpretation of seismological observations are discussed.     

基于散射理论的外源干扰压制法研究

外源干扰在地震道集上表现为符合时距双曲线规律的倒抛物线形状,与震源信号在频谱域内几乎完全重叠,且在其它特征方面无显著差异,因此,常规的噪音压制法无论在时间域或是在频率内都无法实现.本文提出的基于散射理论的外源干扰压制法,是运用观测系统计算和特定点信息,通过外源定位原理,求出外源干扰的位置,通过散射理论模拟任意位置的地震...     

小波理论及其在地震数据处理中的应用

小波理论已成为一个新的数学分支，小波分析已成为地球物理、信号处理、图象处理、理论物理等诸多领域的强有力工具，本文综述了小波理论在地震数据预处理、反演、偏移成像、解释四方面应用研究的最新进展。     

小波理论及其在地震监测中的应用

对小波变换的基本理论和小波分析（多分辨分析、小波包分析）方法做了简要的阐述,介绍了国内外当前小波理论在数字地震监测中的应用研究现状,并在此基础上分析了小波技术在未来数字地震监测中的应用前景。     

基于分块字典学习理论的地震数据去噪

随着油气勘探观测环境愈发复杂,采集的地震数据常常掺杂各种噪声信号,导致勘探目标引起的有效微弱信号被覆盖,严重影响高精度的地震勘探数据解译,因而有效的压制地震勘探数据噪声显得越发重要。本文采用字典学习策略,将复杂地震数据进行分块,通过分块数据的字典学习获取字典原子,构建高精度的字典学习地震数据稀疏表示,通过两次迭代更新字典原子,进行数据去噪。将本文的字典学习算法应用于含随机噪声的模拟数据和实测地震勘探数据处理,验证该算法的可行性及有效性。结果表明,本文算法有效去除了随机噪声,保留了有效信号同相轴,提高了信噪比,可为复杂含噪地震数据的去噪处理提供新的技术手段。     

基于球体位错理论的地震形变分析

地震形变分布特征主要取决于地震断层破裂特征, 不同震级的地震引起的形变响应范围存在差异。 本文中, 我们基于球体位错理论, 以5 mm的形变测量值为基准, 针对逆冲型和走滑型地震断层, 分析了M_W6.0~M_W8.5地震在跨断层法方向上的形变响应范围, 提出了地震震级和响应范围的经验公式, 并与实际地震(2001年昆仑山口西地震、 2013年芦山地震等)结果进行了比较。 比较结果显示, 经验公式计算结果和实际观测值相符合, 可以用于估算M_W6.0~M_W8.5地震在跨断层法方向的形变响应范围, 同时为地震远场形变特征分析与同震、 震后形变测量点布设等方面提供参考数据。     

由同震形变理论计算地震烈度分布的讨论

本文以海地7.3级地震和汶川8.0级地震为例,介绍了同震位移烈度方法,即在已知地震三要素、断层走向、倾向和滑动方向的情况下,可通过计算绝对同震位移来确定地震烈度分布. 研究表明,由绝对同震位移计算的地震烈度分布与实际地震烈度有很好的一致性,特别是在极震区其对应效果更好. 尽管这种计算结果有时与实际情况有一定出入,但这对...     

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.     

基于模糊理论的高铁连续梁桥地震风险评估

以某高速铁路线上一座连续梁桥为例,运用模糊综合评判法,结合基于位移的支座损伤分析和截面曲率的桥墩损伤分析,以全概率理论地震损失模型为基础,提出了基于模糊理论的桥梁系统地震经济风险评估方法。结果表明:综合考虑桥梁系统的模糊地震经济风险分析方法能更全面地计算出连续梁桥在地震作用下的经济损失,仅以桥墩构件代表全桥所得地震经济损失误差较大。基于模糊理论的年预期损失风险框架方法通过结构抗震性能的概率特征可对高速铁路连续梁桥的地震直接经济风险进行全面评估,为该类桥梁的抗震设计、维修加固和灾后重建等方案做出合理评价。     

频率-波数分析基础理论及上海地震台阵响应分析

自1960年开始,地震台阵技术迅猛发展,给地震学研究带来了新的冲击。作为一种新型的研究工具,它主要用来降低全球地震和核爆破的检测阈值和研究地球内部结构。     

深层地震勘探的地震波传传播理论研究前景

深层地震勘探为地震波传播理论研究提出了新的挑战和机遇。深层地震勘探的主要难点是上覆层的影响甚大，使后续的处理有隔靴挠痒之感，必须应用波场延拓消除上覆层影响。深层波速的高速性和横向不均匀性决定了大角散射和弹性波处理方法的重要性。本文具体评述了深层地震勘探的主要方法对策，深入探讨了波场延拓的李群方法和弹性反演的某些问题，目的在于为深化深层地震提供新的研究手段和方法。     

汾渭地震带地震趋势数学建模分析

按照中国大陆及邻近地区活动地块和地震带的划分方案, 使用Mapsis软件选取了汾渭地震带1000年以来M_S4.7以上地震, 这样的地震资料应具有地质单元的统一性。 使用数学中19阶多项式模型, 对地震资料进行最佳逼近拟合, 并递推未来1—2年时间尺度预测。 模型中的参数用最小二乘法求取。 引用一种数学方法来描述汾渭地震带的地震趋势规律。     

深层地震勘探的地震波传播理论研究前景

深层地震勘探为地震波传播理论研究提出了新的挑战和机遇.深层地震勘探的主要难点是上覆层的影响甚大,使后续的处理有隔靴挠痒之感,必须应用波场延拓消除上覆层影响.深层波速的高速性和横向不均匀性决定了大角散射和弹性波处理方法的重要性.本文具体评述了深层地震勘探的主要方法对策,深入探讨了波场延拓的李群方法和弹性反演的某些问题,目的在于为深化深层地震勘探提供新的研究手段和方法.     

重复反射理论在计算地表面地震波时的应用

以某沉淀池设计地震波的计算为例,根据重复反射理论提出一种由典型地震波和土层波阻抗计算场地设计地震波的方法,并证明该计算方法的必要性和可行性.场地覆盖土层假定为无限延伸的水平成层土,基岩面及以下按照线性半无限空间各向同性考虑,基岩面为全反射界面,采用Arkquake软件将初选地震波输入地层,运用等效线性化方法考虑土体非线性,并用傅里叶变换进行频域计算.考虑到各处场地覆盖土层的差异,选用多点分别计算基岩波和地表面地震波.这种方法计算出的地表面地震波能较好地考虑局部场地效应,一定程度上减小地震烈度异常现象,为今后实际工程中地震波的选取提供一种较为实用的参考方法.     

Seismic gaps and plate tectonics: Seismic potential for major boundaries

The theory of plate tectonics provides a basic framework for evaluating the potential for future great earthquakes to occur along major plate boundaries. Along most of the transform and convergent plate boundaries considered in this paper, the majority of seismic slip occurs during large earthquakes, i.e., those of magnitude 7 or greater. The concepts that rupture zones, as delineated by aftershocks, tend to abut rather than overlap, and large events occur in regions with histories of both long- and short-term seismic quiescence are used in this paper to delineate major seismic gaps.In detail, however, the distribution of large shallow earthquakes along convergent plate margins is not always consistent with a simple model derived from plate tectonics. Certain plate boundaries, for example, appear in the long term to be nearly aseismic with respect to large earthquakes. The identification of specific tectonic regimes, as defined by dip of the inclined seismic zone, the presence or absence of aseismic ridges and seamounts on the downgoing lithospheric plate, the age contrast between the overthrust and underthrust plates, and the presence or absence of back-arc spreading, have led to a refinement in the application of plate tectonic theory to the evaluation of seismic potential.The term seismic gap is taken to refer to any region along an active plate boundary that has not experienced a large thrust or strike-slip earthquake for more than 30 years. A region of high seismic potential is a seismic gap that, for historic or tectonic reasons, is considered likely to produce a large shock during the next few decades. The seismic gap technique provides estimates of the location, size of future events and origin time to within a few tens of years at best.The accompanying map summarizes six categories of seismic potential for major plate boundaries in and around the margins of the Pacific Ocean and the Caribbean, South Sandwich and Sunda (Indonesia) regions for the next few decades. These categories range from what we consider high to low potential for being the site of large earthquakes during that period of time. Categories 1, 2 and 6 define a time-dependent potential based on the amount of time elapsed since the last large earthquake. The remaining categories, 3, 4, and 5, are used for areas that have ambiguous histories for large earthquakes; their seismic potential is inferred from various tectonic criteria. These six categories are meant to be interpreted as forecasts of the location and size of future large shocks and should not be considered to be predictions in which a precise estimate of the time of occurrence is specified.Several of the segments of major plate boundaries that are assigned the highest potential, i.e., category 1, are located along continental margins, adjacent to centers of population. Some of them are hundreds of kilometers long. High priority should be given to instrumenting and studying several of these major seismic gaps since many are now poorly instrumented. The categories of potential assigned here provide a rationale for assigning prorities for instrumentation, for future studies aimed at predicting large earthquakes and for making estimates of tsunami potential.Lamont-Doherty Geological Observatory Contribution No. 2906.     

Seismic modelling for geological fractures

Based on knowledge of a commutative group calculation of the rock stiffness and on some geophysical assumptions, the simplest fractured medium may be regarded as a fracture embedded in an isotropic background medium, and the fracture interface can be simulated as a linear slip interface that satisfies non‐welded contact boundary conditions: the kinematic displacements are discontinuous across the interface, whereas the dynamic stresses are continuous across the interface. The finite‐difference method with boundary conditions explicitly imposed is advantageous for modelling wave propagation in fractured discontinuous media that are described by the elastic equation of motion and non‐welded contact boundary conditions. In this paper, finite‐difference schemes for horizontally, vertically, and orthogonally fractured media are derived when the fracture interfaces are aligned with the boundaries of the finite‐difference grid. The new finite‐difference schemes explicitly have an additional part that is different from the conventional second‐order finite‐difference scheme and that directly describes the contributions of the fracture to the wave equation of motion in the fractured medium. The numerical seismograms presented, to first order, show that the new finite‐difference scheme is accurate and stable and agrees well with the results of previously published finite‐difference schemes (the Coates and Schoenberg method). The results of the new finite‐difference schemes show how the amplitude of the reflection produced by the fracture varies with the fracture compliances. Later, comparisons with the reflection coefficients indicate that the reflection coefficients of the fracture are frequency dependent, whereas the reflection coefficients of the impedance contrast interface are frequency independent. In addition, the numerical seismograms show that the reflections of the fractured medium are equal to the reflections of the background medium plus the reflections of the fracture in the elastic fractured medium.     

Seismic hazard assessment for Cyprus

In the present study, probabilistic seismic hazard assessment was conducted for Cyprus based on several new results: a new comprehensive earthquake catalog, seismic source models based on new research, and new attenuation relationships. Peak ground acceleration distributions obtained for a return period of 475 years for rock conditions indicate high hazard along the southern coastline of Cyprus, where the expected ground motion is between 0.3 and 0.4 g. The rest of the island is characterized by values representing less severe shaking. Results of this study strongly indicate the inadequacy of the Turkish Earthquake Code that is being used in the northern part of the island and the Eurocode 8 that is in effect in the southern part of the island to approximate the uniform hazard spectra developed for the high hazard and moderate hazard regions of the island.     

隔震桥梁减震效果分析

本文根据隔震桥梁的设计特点，分别利用非线性水平和转动弹簧单元来模拟减、隔震支座的桥梁延性塑性铰的非线性性能，计及隔震器与减震器的作用对桥梁结构非线性弹塑性动力反应进行了研究。在把桥梁结构和减震器作为整体考虑的情况下，用算例分析了隔震桥梁的减震效果。