弱各向异性介质弹性波的准各向同性近似正演模拟

准各向同性(QI)近似可用于弱各向异性介质的正演模拟.本文通过运用QI方法的零阶和一阶近似,计算了VTI介质模型的地震记录.得出的地震记录与标准各向同性射线理论(IRT)和基于伪谱法的三维地震正演模拟得出的地震记录作了比较,可以认为是精确的合成地震记录.     

模拟地震图纸数字化存储信息录入的设计与实现

本文针对中国地震局正在实施的模拟地震资料抢救项目,对我国现存各类模拟地震图纸进行分类,设计实现了适用于模拟地震图纸扫描基础信息录入软件。首先,通过对图纸图章的分析设计了软件的需求功能,并确定了界面风格;其次,根据图纸扫描工作的保密属性,设计运用xml文件格式将扫描图纸的信息保存在本地文件中;最后,设计了图纸信息录入校验规则以及图纸的命名规则,并实现了异常自动提取和一键生成报表等功能,而且易于使用。本文开发设计的软件不仅降低了大量信息人工录入的错误率,而且显著提升了模拟地震图纸扫描录入与校验的工作效率。通过这项工作所获得的成果数据,便于地震科研工作效率的提高。      

频率域中的合成地震记录

波动理论的合成地震记录是地震资料处理和解释中的重要研究课题。 目前,制作波动理论的合成记录主要是用Trorey的克希霍夫方法,正在研究的有有限差分法和有限元素法。本文提出一种新的方法,在频率域中制作波动理论的合成记录,给出了与克希霍夫绕射波方程等价的频率域中的绕射波方程。在国产DJS-11型计算机上,应用两种绕射波方程实现了合成地震记录,并且进行了比较,认为频率域方法是有效的,可以用于波动方程偏移和地震资料解释,进一步工作有可能获得多层变速模型的波动理论记录。     

The optimum source－time function for generating finite－difference synthetic seismograms

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火山地震的理论地震图计算方法

本文首先分析了不同类型火山地震的波形,提出了相应的震源模型.然后发展了计算层状介质理论地震图的部分分离变量—有限差分方法,其最重要的环节是引用了吸收边界条件,使计算工作得以简化.这种方法特别适用于火山地震的理论地震图计算.最后,本文给出了计算实例.     

The strain seismograms of P- and S-waves of a local event recorded by four-gauge borehole strainmeter

At a sampling rate of 100 samples per second,the YRY-4 four-gauge borehole strainmeters(FGBS) are capable of recording transient strains caused by seismic waves such as P and S waves or strain seismograms. At such a high sampling rate, data from the YRY-4 strainmeters demonstrate fairly satisfactory self-consistency. The strain tensor seismograms demonstrate the senses of motion of P waves, that is, the type of seismic wave travels in the direction of the maximum normal strain change. The observed strain patterns of S waves significantly differ from those of P waves and should contain information about the source mechanism. Spectrum analysis shows that the strain seismograms are consistent with conventional broadband seismograms from the same site.     

TheoreticalPKP seismograms near the caustic calculated by sum of reflected waves

Summary This paper gives some examples of theoretical seismograms of PKP waves near the caustic. Seismograms of refracted waves for the original medium are compared with seismograms composed as a sum of the reflected waves, generated at boundaries of a substitute medium. All seismograms are calculated by zero approximation of the ray theory. The influence of some parameters of the source function and of the substitute medium on the results is shown.     

Digitized Database of Old Seismograms Recorder in Romania

The aim of this paper is to describe a managing system for a unique Romanian database of historical seismograms and complementary documentation (metadata) and its dissemination and analysis procedure. For this study, 5188 historical seismograms recorded between 1903 and 1957 by the Romanian seismological observatories (Bucharest-Filaret, Foc?ani, Bac?u, Vrincioaia, Câmpulung-Muscel, Ia?i) were used. In order to reconsider the historical instrumental data, the analog seismograms are converted to digital images and digital waveforms (digitization/ vectorialisation). First, we applied a careful scanning procedure of the seismograms and related material (seismic bulletins, station books, etc.). In a next step, the high resolution scanned seismograms will be processed to obtain the digital/numeric waveforms. We used a Colortrac Smartlf Cx40 scanner which provides images in TIFF or JPG format. For digitization the algorithm Teseo2 developed by the National Institute of Geophysics and Volcanology in Rome (Italy), within the framework of the SISMOS Project, will be used.     

历史地震图数据库及共享平台

历史地震图纸是记录历史地震的重要资料,在进行电子化之前,图纸的唯一性限制了其大范围共享的可能。电子化处理是抢救和保护历史地震图纸的重要手段,可以有效发挥其使用及研究价值,具有重要意义。为此研制历史地震图数据库及共享平台,对北京国家地球观象台现存的60万张历史地震图纸进行高精度(600 dpi)扫描和规则化命名,利用数据库和FastDFS分布式文件系统进行统一存储,并采用多级缩略图和网络服务方式提供数据共享服务。     

Predictive deconvolution applied to long-range seismic refraction observations

Summary The method of predictive deconvolution is described and applied to seismograms from the 1963 Lake Superior experiment. The process is successful in removing shot-generated reverberations and sometimes reveals seismic phases which are not easily identifiable on the original seismograms.     

使用地面单台三分向地震记录资料评估场地效应方法的研究

利用唐山强震观测台阵提供的井下和地面数字测震资料，研究了用单台地震记录评估场地效应的方法。利用井下基岩地震记录作参考台，用地面和井下的记录求取经验传递函数。同时应用Nakamura单台评估方法求解Nakamura谱比率。通过对比，证实了对场地效应的评估可以使用地面单台测震资料进行，不必参考基岩台的资料。因此，该方法是评估重要工程场地效应的一种简便可行的方法。使用该方法可以降低地震小区划的成本。     

Cross-correlation Coefficients for the Study of Repeating Earthquakes: An Investigation of Two Empirical Assumptions/Conventions in Seismological Interpretation Practice

For the identification and analysis of ‘repeating earthquakes,’ there are two empirical concepts. The first is the assumption that the cross-correlation coefficient of the filtered seismograms of closely spaced ‘repeaters’ depends exponentially on the inter-event separation distance. The second is the convention that in processing regional seismograms, a 0.5–5.0-Hz band pass filter is used. In this article, using a simple layered structure model, we investigated the cross-correlation coefficient of the filtered synthetic seismograms of two closely located events, that is, a ‘doublet.’ We investigated the relation between the cross-correlation coefficient and the inter-event separation distance. Simulation shows that in the 0.5–5.0-Hz frequency band, even if for simple synthetic seismograms without considering lateral heterogeneity or scattering, the exponential dependence is only a first order approximation concept. To check the frequency dependence of the cross-correlation coefficient, we analyzed a group of seismograms of a ‘multiplet’ in Xiuyan, Liaoning, northeast China, recorded by the Regional Seismographic Network of Liaoning Province. The cross-correlation coefficients were observed to be relatively stable against frequency for the 0.5–5.0-Hz frequency band.     

Seismogram Synthesis in Multi-layered Half-space Part Ⅰ. Theoretical Formulations

In the past two decades numerous studies were made to develop and improve the theory and practical computation techniques of synthesizing theoretical seismograms for the model of multi-layered half-space. Today, synthesizing theoretical seismograms in multi-layered half-space is an important tool for understanding the structure of the Earth's interior as well as the seismic source process from well-recorded seismograms data. As part of a review of the state-of-the-art, in this article I shall present a systematic and self-contained theory of elastic waves in multi-layered half-space media based on the developments in the past two decades.     

Study on the Method for Obtaining Acceleration Waveform Records from Velocity Type Seismograms of the Digital Seismograph Network

The authors proposed a method for obtaining high-quality acceleration seismograms from velocity type seismograms of digital Seismographic network, and took as an example the analysis and processing of the seismograms of a same earthquake that was simultaneously recorded by velocity seismograph CTS1-EDAS24 and strong motion seismograph EST-Q4128 installed in Jixian Station, Tianjin. The calculation steps and the processing method have been discussed in detail. From the analysis and the comparison of the obtained results, it is concluded that the proposed method is simple and effective, and it broadens the application of digital seismographic network.     

层状介质中内源引起的地震波理论地震图的部分分离变量——有限差分计算方法

文献〔1〕给出了震源在地表时计算理论地震图的部分分离变量——有限差分方法。本文继〔1〕讨论了震源在介质内部时,特别是震源在介质分界面上时理论地震图的计算方法。含贝塞尔函数的数值积分是用FiLon方法完成的,它具有精度高,运算速度快的特点。作为例子,本文最后给出了利用所述计算方法得到的不同内源在含两个高速夹层地壳模型中的理论地震图。     

噪声水平上的爆炸余震信号提取

文中采用窄带滤波、傅里叶反变换及小波分析在噪声水平上提取弱余震信号。窄带滤波能够在背景噪声水平上以及（－10）－（20）dB记录中提取有用信息，但是往往产生截断误差，如果数字序列具有较大的初始幅值，所提取的波形在截断处发生畸变。傅氏反变换从负信噪比的记录中提取的信号质量较差，伴有高频干扰成分，对于信噪比为正数的记录，傅氏反变换提取的波形是良好的，该种方法同滤波方法一样，也存在截断误差。小波分析从信噪比为负数的记录中提取的信号不理想，而从信噪比为正数的记录中提取的信号质量最好，波形完整，首尾清晰，基线平直，无截断误差。窄带滤波，傅氏反变换及小波分析有两个共同点，基一，都能够从强背景噪声中提取有用信息；其二，信噪比越大，获取的信号质量越高。     

LEVINSON INVERSION OF EARTHQUAKE GEOMETRY SH-TRANSMISSION SEISMOGRAMS IN THE PRESENCE OF NOISE*

The Kunetz-Claerbout equation for the acoustic transmission problem in a layered medium in its original form establishes the relation between the transmission and the reflec tion response for P-waves in an horizontally layered medium and with vertical incidence. It states that the reflection seismogram due to an impulsive source at the surface, is one side of the autocorrelation of the seismogram due to an impulsive source at depth and a surface receiver. By adapting Claerbout's formulation to the transmission of SH-waves, the Kunetz-Claerbout equation also holds for reflection and transmission coefficients dependent on the incident angle. Thus, earthquake geometry SH-transmission seismograms can be used to caculate corresponding pseudoreflection seismograms which, in turn, can be inverted for the impedance structure using the Levinson algorithm. If the average incidence angle is known, a geometrical correction on the resulting impedance model can improve the resolution of layer thicknesses. In contrast to the inversion of reflection seismograms, the Levinson algorithm is shown to yield stable results for the inversion of transmission seismograms even in the presence of additive noise. This noise stabilization is inherent to the Kunetz-Claerbout equation. Results of inverted SH-wave microearthquake seismograms from the Swabian Jura, SW Germany, seismic zone obtained at recording site Hausen im Tal have been compared with sonic-log data from nearby exploration drilling at Trochtelfingen. The agreement of the main structural elements is fair to a depth of several hundred metres.     

SYNTHESIS OF ACOUSTIC WELL-LOGGING WAVEFORMS ON AN IRREGULAR GRID*

The need for synthetic seismograms arises in several acoustic well-logging contexts. We propose a numerical algorithm for computing the seismograms, characterized by a very reduced computational cost. Unlike previous contributions appearing in the technical literature, the proposed algorithm is based on a non-uniform sampling step and on linear interpolation for computing the integrals involved in the synthesis.     

单台识别核爆的方法初探

根据乌鲁木齐地震台记录的国外６个主要核试验基地的核爆地震记录资料，通过对振动波形、首波振幅Ｐ１、最大纵波振幅Ｐｍ、最大横波振幅Ｓｍ及体波震级ｍｂ、面波震级Ｍｓ之间一些关系的研究，找出了核爆记录与天然地震记录的差别，为单台正确识别核爆提供了基本方法。     

Synthetic P-wave seismograms for the Kinnaur (Himachal Pradesh,India) earthquake of January 19, 1975

Long-period P-wave seismograms are computed for the Kinnaur earthquake of January 19, 1975, using a bilateral-bidirectional propagating rectangular fault model. Comparison of computed and observed P-wave seismograms shows good agreement. Hence, it is inferred that a bilateral-bidirectional fault is a suitable model for this earthquake.