消除强震加速度记录数字化误差的方法和处理软件

本文详细地分析了用数字化仪和激光扫描仪对模拟加速度记录进行数字化时所产生的误差及消除这些误差的方法，并开发了相关处理软件。数字化误差由数字化设备的系统误差和读数员在操作过程中的随机误差迭加而成，随机数字化误差是具有各态历经性质的、其振幅按高斯规律分布的平稳随机过程。利用激光扫描仪做强震记录数字化，工作效率很高。本文给出了激光扫描仪分析处理软件和消除数字化噪声实例。     

Brief history of computation of earthquake response spectra

The methods for computation of response spectrum amplitudes are reviewed for the period preceding the modern digital computer age. The mechanical and electrical analog methods that preceded the modern digital calculations were time consuming, inaccurate, and difficult to verify. Modern studies of response and of the nature of strong ground motion became possible after mid-1960 with accumulation of strong-motion records and with accurate digitization and digital data processing.     

Creation of a Digital Database for XXth Century Historical Earthquakes Occurred in the Iberian Area

—The problems of recovering the seismic information contained in the old seismograms through their digitization and processing by computer methods are discussed. We present the main principles of a simple manual technique for digitization of early seismic records of the Wiechert seismograph. Detrending of the zero-line slope, circular arc removal, smoothing and interpolation treatment of the digital data are made. The accuracy of the digitizing process is assessed and its reliability is tested by a comparison with automatically obtained digital data and their spectral amplitudes. The deconvolution of the seismograph response has allowed us to obtain the time variation of ground motion which is then contrasted with direct measurements of ground motion displacement amplitudes given in the old-time bulletins. We have created a digital database for historical earthquakes which occurred in the Iberian area during the period 1912–1940 and recorded by the Wiechert seismograph at the Geophysical Observatory of Toledo, Spain. It contains the following output data the digitized original records; the geometrically corrected and interpolated data; the time variation of ground motion; maximum amplitudes and corresponding periods; total duration of the seismic oscillations and amplitude spectra. We carry out magnitude estimates and give formulae for magnitude classification based on the signal duration and on the maximum ground displacement amplitude. We also perform seismic moment determinations by spectral analysis of waveforms and propose a new seismic moment-magnitude relation.     

CBMD磁照图数字化软件的研制

介绍了图像处理技术在模拟磁照图数字化中的应用，使用该方法研制的CBMD软件通过二值化、细线化等关键图像处理技术对磁照图进行处理，最终实现模拟图纸的数字化。     

数字化噪声对强震记录的影响及其消除方法

本文详细地分析了强震加速度记录的数字化噪声。分析表明:数字化噪声由数字化设备的系统误差和操作者的随机读数误差迭加而成,随机数字化误差是具有各态历经性质的,其振幅按高斯规律分布的平稳随机过程,在其频谱组成中,长周期分量占明显的优势,因此将对二次积分加速度记录的位移曲线产生严重的影响。 研究表明:随机数字化噪声位移主要分布在周期大于25秒的频段,对加速度记录来说,分布在周期小于25秒的频段内,其随机噪声是相当小的(假定记录纸速为1厘米/秒)。因此,利用数字滤波技术,可以除去数字化加速度记录中的大部份随机数字化噪声。 作为实例,对一个典型的强震加速度记录进行了滤波,给出了低噪声的加速度记录和由此算出的位移曲线,且和未经滤波的相应记录及其位移进行了比较。      

Determination of noise spectra from strong motion data recorded in Greece

A large number of strong ground motions inGreece have been recorded by analogaccelerographs. The processing of analogstrong motion recordings and conversion toa digital form introduces noise in thesignal, due to the digitization andprocessing whichsignificantly affects the record. In thepresent paper a unified processing anddetermination of digitization andprocessing noise for the Greek strongmotion records is presented. Moreover,appropriate relations are proposed for thelower cut-off frequency with respect tothe epicentral distance and earthquakemagnitude for record filtering.     

数字仪与模拟仪地震处理的对比分析及近震走时表的修改

利用都兰地震台数字地震仪记录资料，在地震处理中使用修改后的走时表，可以实现从模拟到数字的顺利过渡，更好的使用数字化食品进行地震观测。通过传递函数仿真计算震级的对比以及走时表修改后与修改前震中距的对比分析，找出了两的差异和结合点。     

如何提高磁照图数字化的精度

CBMD是一款针对CB-3模拟磁照图进行数字化处理的软件,利用专业图像处理技术,对模拟磁照图进行数字化,由于模拟仪器调试及存放因素造成了图纸状况不尽相同,使用者在数字化处理过程中,根据不同的图,纸采用相应的方法进行处理,才能保证数字化结果精确度.本文就主要的几种影响处理精度的情况展开讨论,并提出具体的解决方法.     

COMPUTER PROCESSING OF AIRBORNE ELECTROMAGNETIC DATA *

With the increasing number of channels in AEM systems, computer data handling is becoming a necessity. The experience gained in processing of seismic and aeromagnetic data cannot be applied directly to low-frequency (100-5000 Hz) AEM methods. A novel scheme has been designed for AEM data processing and tested on 2900 km (1800 miles) of Input surveys. In the first step, the digital flight tapes are merged with digitized flight path recovery to form the primary data set. The validity of the raw data is controlled by the computer, but the interpreter has an option of checking them in perspective plots of channel amplitudes. The primary data set is reduced by processors which determine the location and type of anomalies and discard noise. Unlike the widely used deconvolution, the sequential processor determines first the anomaly location and then estimates parameters, such as peak amplitude, base width, and excess area, which are used as acceptance criteria. Interpretation parameters, such as σt, conductor depth, and dip are estimated by comparison with quantitative models. The recorded channel amplitudes are plotted together with the selected interpretation parameters in a profile form. The secondary data set which includes only the interpretation parameters for selected anomalies is graphically displayed as a schematic map of apparent σt. Elongated features are traced by a fan strike recognition routine and a trend map is automatically compiled and plotted. Disk storage is essential for second pass processing during which parts of the primary data set are searched for undiscovered anomalies matching the analyzed trend. The suggested procedure for AEM data processing is demonstrated on an Input MK V survey, Southern Indian Lake, Manitoba.     

地下流体数字化改造中几个技术性问题的探讨

总结了地下流体前兆台站数字化改造中遇到的问题, 对出现的问题进行分析研究并探索解决方法。 介绍了井口、 脱气、 集气装置的原理和制作方法。 对比分析了数据传输中几种不同方法的优缺点, 为“十五”地下流体前兆台网数字化改造和未来地下流体台网的建设提供了科学依据。     

基于EMD的信号瞬时特征的小波分析方法

提出了一种基于EMD(Empirical Mode Decomposition)的信号瞬时特征的小波分析方法。用这种方法提取非平稳信号的瞬时频率和瞬时幅值分三个基本步骤：首先,用EMD把信号分解成IMF(Intrinsic Mode Function)分量;接着,对IMF分量进行小波分析,从小波系数的幅角函数中提取小波脊线;最后,从小波脊线中提取瞬时频率和瞬时幅值。通过对仿真信号的分析,验证了该方法能有效地分析非平稳信号。     

Fractured reservoir delineation using multicomponent seismic data

The characteristic seismic response to an aligned-fracture system is shear-wave splitting, where the polarizations, time-delays and amplitudes of the split shear waves are related to the orientation and intensity of the fracture system. This offers the possibility of delineating fractured reservoirs and optimizing the development of the reservoirs using shear-wave data. However, such applications require carefully controlled amplitude processing to recover properly and preserve the reflections from the target zone. Here, an approach to this problem is suggested and is illustrated with field data. The proposed amplitude processing sequence contains a combination of conventional and specific shear-wave processing procedures. Assuming a four-component recording (two orthogonal horizontal sources recorded by two orthogonal horizontal receivers), the split shear waves can be simulated by an effective eigensystem, and a linear-transform technique (LTT) can be used to separate the recorded vector wavefield into two principal scalar wavefields representing the fast and slow split shear waves. Conventional scalar processing methods, designed for processing P-waves, including noise reduction and stacking procedures may be adapted to process the separated scalar wavefields. An overburden operator is then derived from and applied to the post-stacked scalar wavefields. A four-component seismic survey with three horizontal wells drilled nearby was selected to illustrate the processing sequence. The field data show that vector wavefield decomposition and overburden correction are essential for recovering the reflection amplitude information in the target zone. The variations in oil production in the three horizontal wells can be correlated with the variations in shear-wave time-delays and amplitudes, and with the variations in the azimuth angle between the horizontal well and the shear-wave polarization. Dim spots in amplitude variations can be correlated with local fracture swarms encountered by the horizontal wells. This reveals the potential of shear waves for fractured reservoir delineation.     

Common problems in automatic digitization of strong motion accelerograms

Common problems encountered in automatic digitization of strong motion accelerograms, recorded on film, are presented and discussed. These include synchronization of the time scale for the three components of motion, non-uniform film speed, trace following in case of scratches or trace crossings, distortions from high contrast preprocessing of the scanned image, and trace “rotation” resulting from rotated position of the scanned film record. Procedures for correcting or eliminating these problems are suggested. The image processing hardware has developed so much during the past 20 years, that at present it exceeds the technical requirements for processing strong motion accelerograms. The problems described in this paper result from lack of training of the operators and lack of quality control in the process, which still seems to be esoteric and highly specialized. This situation may have been caused by the low demand by the engineering profession for high quality and large volume of strong motion data.     

基于共炮偏移的AVO反演

常规AVO多是利用CMP道集的振幅进行反演。主要有三个方面影响其精度:首先,CMP道集假设地下为水平层状介质,但是实际地下介质多为倾斜地层,地层倾角越大CMP道集的振幅所反映地下介质的位置与实际位置差距就越大。其次,NMO、DMO和反褶积等常规处理流程,都会造成振幅值失真。第三,反演所用的反射系数公式是与入射角有关的量,而欲从CMP道集得到准确的入射角与振幅之间的对应关系,则十分困难。波动方程叠前深度偏移除对复杂介质和陡倾角地层具有较强的成像能力,还可以最大限度的减少常规处理所带来的误差并使振幅归位。本文综合了保幅偏移、角度道集提取以及AVO反演等前人的工作,提出直接从炮集数据反演AVO属性的方法,以期显著减少上述三个因素对AVO反演精度的影响。     

CORRELATION PATTERNS IN CHARACTERISTICS OF SPATIALLY VARIABLE SEISMIC GROUND MOTIONS

A methodology for the investigation of the spatial variation of seismic ground motions is presented; data recorded at the SMART-1 dense instrument array in Lotung, Taiwan, during Events 5 and 39 are used in the analysis. The seismic motions are modeled as superpositions of sinusoidal functions, described by their amplitude, frequency, wavenumber and phase. For each event and direction (horizontal or vertical) analysed, the approach identifies a coherent, common component in the seismic motions at all recording stations, and variabilities in amplitudes and phases around the common component sinusoidal characteristics, that are particular for each recording station. It is shown that the variations in both the amplitudes and the phases of the motions at the station locations around the common component characteristics contribute significantly to the spatially variable nature of the motions, and, furthermore, they are correlated: increase in the variability of the amplitudes of the motions recorded at individual stations around the common amplitude implies increase in the variability of the phases around the common phase. The dispersion range of the amplitude and phase variability around their corresponding common components appear also to be associated with physical parameters. The spatially variable arrival time delays of the waveforms at the stations due to their upward travelling through the site topography, in addition to the wave passage delays identified from signal processing techniques, constitute another important cause for the spatial variation of the motions; their consideration in the approach facilitates also the identification of the correlation patterns in the amplitudes and phases. © 1997 by John Wiley & Sons, Ltd.     

A new direction for shallow refraction seismology: integrating amplitudes and traveltimes with the refraction convolution section

The refraction convolution section (RCS) is a new method for imaging shallow seismic refraction data. It is a simple and efficient approach to full‐trace processing which generates a time cross‐section similar to the familiar reflection cross‐section. The RCS advances the interpretation of shallow seismic refraction data through the inclusion of time structure and amplitudes within a single presentation. The RCS is generated by the convolution of forward and reverse shot records. The convolution operation effectively adds the first‐arrival traveltimes of each pair of forward and reverse traces and produces a measure of the depth to the refracting interface in units of time which is equivalent to the time‐depth function of the generalized reciprocal method (GRM). Convolution also multiplies the amplitudes of first‐arrival signals. To a good approximation, this operation compensates for the large effects of geometrical spreading, with the result that the convolved amplitude is essentially proportional to the square of the head coefficient. The signal‐to‐noise (S/N) ratios of the RCS show much less variation than those on the original shot records. The head coefficient is approximately proportional to the ratio of the specific acoustic impedances in the upper layer and in the refractor. The convolved amplitudes or the equivalent shot amplitude products can be useful in resolving ambiguities in the determination of wave speeds. The RCS can also include a separation between each pair of forward and reverse traces in order to accommodate the offset distance in a manner similar to the XY spacing of the GRM. The use of finite XY values improves the resolution of lateral variations in both amplitudes and time‐depths. The use of amplitudes with 3D data effectively improves the spatial resolution of wave speeds by almost an order of magnitude. Amplitudes provide a measure of refractor wave speeds at each detector, whereas the analysis of traveltimes provides a measure over several detectors, commonly a minimum of six. The ratio of amplitudes obtained with different shot azimuths provides a detailed qualitative measure of azimuthal anisotropy and, in turn, of rock fabric. The RCS facilitates the stacking of refraction data in a manner similar to the common‐midpoint methods of reflection seismology. It can significantly improve S/N ratios.Most of the data processing with the RCS, as with the GRM, is carried out in the time domain, rather than in the depth domain. This is a significant advantage because the realities of undetected layers, incomplete sampling of the detected layers and inappropriate sampling in the horizontal rather than the vertical direction result in traveltime data that are neither a complete, an accurate nor a representative portrayal of the wave‐speed stratification. The RCS facilitates the advancement of shallow refraction seismology through the application of current seismic reflection acquisition, processing and interpretation technology.     

香港数字化地震监测台网

香港天文台于１９９７年建立了一套设有８个短周期地震台站的地震监测网络。台网运用数字化及实时数据传送和处理等技术,增强地震数据接收及分析的效能和准确性。本文介绍了地震台站的选址和监测系统的特性与功能。     

地震监测模拟记录图纸数字化

大量地震监测模拟记录图纸面临腐烂和损坏,模拟记录资料数字化是挽救此成果的一种办法,在模拟记录图纸中,代表时点的纵轴线存在直线轴和曲线轴2种类型。为实现地震监测模拟记录图纸数字化,分析并提出轴线、记录曲线的数字化解决方法,基于Matlab实现影像读取、图像旋转、轴线匹配、曲线跟踪、数值转换、导出"时点—测量值"数据表等功能,并通过实例展现模拟图纸数字化成果,为验证成果的可靠性,将数字化与人工读取成果进行比较,发现二者具有一致性。     

VERTICAL SEISMIC PROFILING—SEPARATION OF P- AND S-WAVES*

In vertical seismic profile's (VSP's) shot with a large source offset, rays from shot to receiver can have large angles of incidence. Shear waves generated by the source and by conversions at interfaces are likely to be recorded by both the vertical and the horizontal geophones. Varying angles of incidence may give strong variations in the recorded amplitudes. Separation of P- and SV-waves and recovery of their full amplitudes are important for proper processing and interpretation of the data. A P-S separation filter for three-component offset VSP data is presented which performs this operation. The separation filter is applied in the k-f domain and needs an estimate of the P- and S-velocities along the borehole as input. Implementation and stability aspects of the filter are considered. The filter was tested on an 1800 m offset VSP and appeared to be robust. Large velocity variations along the borehole could be handled and results were superior to those obtained by velocity filtering.     

Preliminary empirical model for scaling fourier amplitude spectra of strong ground acceleration in terms of modified mercalli intensity and recording site conditions

This paper presents an empirical model for scaling Fourier amplitude spectra of ground acceleration during strong earthquake shaking in terms of the reported Modified Mercalli Intensity (MMI) and the simplified characteristics of the geologic environment at the recording station. This analysis shows that (i) for the intermediate and high-frequency motions the spectral amplitudes approximately double for every level of the MMI; that (ii) the uncertainties associated with estimation of Fourier spectral amplitudes in terms of MMI are not greater than the uncertainties associated with similar estimation in terms of earthquake magnitude and epicentral distance; that (iii) the high frequency spectral amplitudes tend to be greater on basement rock sites relative to alluvium sites, with this trend being reversed for the low-frequency spectral amplitudes; and that (iv) the spectral amplitudes of very high-frequency vertical shaking are equal to or higher than the corresponding spectral amplitudes for horizontal shaking.