SIGNIFICANCE OF INFORMATION UNCERTAINTY IN SETTING UP THE INTERPRETATIVE PATTERNS OF GEOPHYSICAL DATA*

Geophysical interpretation consists of the identification of geological parameters carried out in the state of uncertainty. From this follows that the identificative model must correspond to the degree of uncertainty. As uncertainty measure of the surveyed material the informative distance between different interpretive models is introduced. The influence of the measurement noise and the accuracy of measurement devices as well as the number of measurement sets worked out simultaneously for this survey is analyzed. Numerical examples indicate that the material considered to be not interpretable from the point of view of a certain accurate model may be interpreted by the use of a less accurate model.     

A NOTE ON THE LINEAR FILTER METHOD OF INTERPRETING RESISTIVITY SOUNDING DATA*

In the linear filter method of interpreting resistivity sounding data, as developed by Ghosh (1971), it appears that the filter function in the x-domain approaches an oscillating function for both large positive and large negative abscissa values. In the present note the reason for this oscillating behaviour is derived, and a possible practical application is indicated.     

GEOPHYSICAL CATEGORIZATION OF THE PRECAMBRIAN IN SOUTH INDIA*

The ground follow-up of a magnetic and radiometric air survey had to cope with the usual dilemma to check a great number of anomalies within a short time. A limited aggregate of magnetic anomalies, expected to correspond to magnetite quartzites was statistically selected for ground identification by this method: the ratios length/width times amplitude were listed for all coherent contours and the calculation of the standard deviation per unit area resulted in different key-numbers for a new lithological “Salem Unit” and for the charnockitic or gneissic environment. The ground work thus directed and reduced by 85% yielded a substantial potential of iron ore. This was supported by by abundant determinations of the magnetic susceptibilities, confirming the sources of anomalies and revealing the amenabilities of iron ores for the magnetic separation process. The lines of truncation of anomalies were found to represent a system of local and regional faults and shear zones, which segregated the area into different tectonic blocks. These sutures have also provided the ways of intrusion for alkaline and basic magmae in the style of a “Rift” structure, housing several carbonatites and impregnations of metal sulphides. The airborne radiometrics obtained many uranium indications by gamma ray spectrometry. However, they led only to disseminated uranium-silicates, associated with syenites, granites and pegmatites, each emanating a characteristic photon energy spectrum. But in general the radiation of thorium prevails, marking northern Madras as a “Thorium Province”.     

DQ-87型地球物理数据采集和处理系统

在地球物理学领域内经常遇到各种观测资料,其信号频率范围属于甚低频和超低频。例如地磁脉动,由电离层反射的无线电波频率的多普勒偏移,哨声,声重力波以及一般的地磁、地电、地震资料,大气参量的变化及其湍动等等,它们的频率范围从千分之几赫兹到数千赫兹。这些资料的收集和整理通常是分开的,由于记录的资料通常并不是数据化的,     

DQ-87型地球物理数据采集和处理系统

在地球物理学领域内经常遇到各种观测资料,其信号频率范围属于甚低频和超低频。例如地磁脉动,由电离层反射的无线电波频率的多普勒偏移,哨声,声重力波以及一般的地磁、地电、地震资料,大气参量的变化及其湍动等等,它们的频率范围从千分之几赫兹到数千赫兹。这些资料的收集和整理通常是分开的,由于记录的资料通常并不是数据化的,     

THE USE OF THE CONTINUOUS SEISMIC PROFILER TO SOLVE HIDDEN LAYER PROBLEMS*

Integration of the continuous seismic reflection profiler with the marine refraction method on engineering surveys offers a solution to hidden layer problems, allowing both layer velocity and thickness to be computed.     

西部地下水勘查的基础地质问题与关键地球物理技术

介绍了基础地质问题研究对西部深层地下水文地质研究的重要意义，就西部地下水研究的特殊性，针对性地提出了地球物理的解决方法和思路，在利用已有的地球物理资料研究基础地质问题的过程中，介绍重要的地球物理方法技术及研究工作步骤，针对这些方法技术在应用中面临的问题和技术本身存在的不足，提出了具体解决方案和研发部署，针对已有资料的局限性和西部地下水的特殊性，提出研究高精度地震静校正、全波处理等方法技术。     

TOWARDS UNIFICATION OF GEOPHYSICAL PROBLEMS FOR HORIZONTALLY STRATIFIED MEDIA*

Theorems and relations describing a system of horizontal layers are considered as the elements of a meta-system having a layered structure. This implies a layered structure of a solution of geophysical problems for horizontally stratified medium. Wave equation, Laplace's equation, and Maxwell's equations are the special cases of a more general differential equation. By separation of variables the basic equation for layered structures is obtained. A multi-layer medium may result from accumulation of successive layers. The descending or ascending accumulation is possible, depending whether the successive layers are inserted at the top or at the bottom of the medium. The discretization of a basic equation provides two sets of formulas for descending or ascending accumulation, respectively. The relationship between the mathematical expressions of the seismic transfer function and the magnetotelluric input impedance is derived. The deduction leads to the possibility of converting the magnetotelluric observations into an equivalent synthetic seismogram.     

磁激发极化法探矿理论的几个问题

本文对磁激发极化法当前存在的几个探矿理论问题进行了讨论,指出了某些著作中的错误及不完善之点,提出了作者的观点,给出了新的理论公式和异常剖面曲线以及某些条件下的室内模型实验结果和野外实际资料。     

磁激发极化法探矿理论的几个问题

本文对磁激发极化法当前存在的几个探矿理论问题进行了讨论,指出了某些著作中的错误及不完善之点,提出了作者的观点,给出了新的理论公式和异常剖面曲线以及某些条件下的室内模型实验结果和野外实际资料。     

THE USE OF COMPUTER GRAPHICS IN GRAVITY INTERPRETATION*

Computer-Graphics, the visual display of data in digital and analog form, allows immediate interaction between man and machine. This interaction facility is valuable when the user is engaged in model design. By using such a device in gravity interpretation, the geophysicist can overcome the slow process of model simulation constrained by the conventional input/output devices, also maximum control over running programmes can be exerted if needed.     

STATISTICAL MULTIVARIATE ANALYSIS OF AIRBORNE GEOPHYSICAL DATA ON THE SE BORDER OF THE CENTRAL LAPLAND GREENSTONE COMPLEX*

Statistical multivariate methods for the integrated processing of airborne geophysical data were tested. The data consisted of magnetic, electromagnetic and gamma radiation measurements, to which cluster analysis, principal components analysis and discriminant analysis were applied. Also, auxiliary variables were derived from the original ones and their value was tested. Although the frequency distributions of the data do not favour statistical analysis, the practical results are acceptable. Principal component analyses show geological and technical aspects that are difficult to obtain from the original observations. In cluster analyses, the sources of measured fields control the grouping of variables. Discriminant analysis was applied to the automatic identification of rocks by geophysical data. The rocks investigated are metasediments and metavolcanics, some magnetic and others conductive. When all available geophysical data were included, correct identifications were made in more than 60% of cases. In particular, gamma ray observations were found to improve the discrimination of non-magnetic and non-conductive rocks. The geophysical similarity of rocks studied by cluster analysis depends on electrical and magnetic properties as well as on their origin; the content of radioactive elements in turn is related to the origin.     

INTERPROFILE CORRELATION AND SELF-SETTING FILTRATION METHODS OF ANALYSIS OF GEOPHYSICAL DATA *

Application of statistical methods of analysis of geophysical data is often helpful for the detection of weak anomalies against a noisy background. The processing and analysis of areal geophysical data by two such methods are presented. The advantage of these methods are illustrated with the help of two field examples.     

GEOPHYSICAL DATA BASES: SYSTEM CONSIDERATIONS*

The use of data file systems within the areas of geological well log and reservoir analysis is now accepted as a necessity in the storage and correlation of large volumes of diverse information. Multi-channel and three-dimensional seismic recording techniques of various types result in a situation where the amount of processing parameters and derived seismic properties of a trace are rapidly approaching the amount of the recorded data themselves. The requirement to access these statistics efficiently has introduced the problems of data management to the seismic processing community. Much software effort has been expended in the design of algorithms for cross reference and indexing of the statistics required in signal processing. These efforts, however, are generally in the direction of a localized solution to a specific requirement and tend to ignore the data base concepts well developed within the commercial data processing community. This paper examines the applicability of commercial data base concepts to the problems of data handling in the area of geophysical exploration, sets forth some basic definitions and organizational characteristics, and describes a system for the integration of several earth disciplines within a single data base from which parameters and mapped information may be derived and indexed for the purpose of processing and interpretation.     

THE POTENTIAL OF SHEAR-WAVE OBSERVATIONS*

Shear waves can today be generated and observed, though not with the flexibility and the technical standard of compressional waves, and they can be identified in seismograms by various means. Their potential lies not so much in their lower velocity (corresponding—for the same frequency—to shorter wavelength and higher resolution) but in the fact that they probe the earth with stresses and strains that differ from those of compressional waves. Full utilization of the information potential of shear waves, therefore, requires combined use of P-and S-waves. Complications in the combined use of different wave types should be regarded as opportunities to obtain additional information. A typical example is the observation that the depth of one and the same interface estimated on the bases of P- and SH-reflections, respectively, can differ significantly. This discrepancy may be due to the anisotropy of a finely layered medium. Under favorable circumstances some of the parameters describing this anisotropy can be deduced from the different depth estimates and the curvature of the squared-offset/squared-time representation of the different reflections. Since in anisotropic media vertically polarized shear waves are significantly different from horizontally polarized ones, the combined observation of all three waves opens up additional possibilities.     

宁夏跨断层水准测量资料震前异常指标分析

通过分析宁夏跨断层水准测量资料,总结了水准资料在宁夏及其临区中强地震前的异常指标,并分析了贺兰山东麓断裂带的活动性。     

中国地震历史资料的信息开发与利用

本文对全国历史地震资料的有用信息作了进一步的开发和利用，按统一方法处理了大量有感以上地震的文字记载，确字每个独立地震的时间与地点；分区求得地震的有感区长半径与震级的关系式；确定了历史有感地震的最低震级为４；取得了８０００余次有感地震垢基本参数；用等震线测定了巨大地震的参数；将有感强震目录统编成全国与几个大区Ｍ≥４．０地震目录，按《地震学地震预报实用程序系统》（ＥＰＳＥＩＳ）的格式要求建库；同时编制     

THE USE OF A SQUARE CONFIGURATION IN RESISTIVITY PROSPECTING *

Consideration is given to the use of a configuration of four electrodes set in a square array for resistivity measurements. It is found that, by passing current successively between different pairs of electrodes, an apparent resistivity can be determined which is both more sensitive to the position of the array centre and less dependent on orientation than the measures usually obtained with colinear arrays of electrodes. At the same time the observations made enable the degree of the departure of local conditions from conditions of lateral homogeneity to be assessed. Theoretical and practical examples of the use of this electrode system are given and the use of the system both as a tool in mapping and in depth investigations is considered. It is shown that provided electrode spacings are suitably arranged the results of a probe carried out using the square array can be interpreted by conventional methods. The system is shown to have particular advantages in the investigation of lateral resistivity variations and the reduced dependence on orientation makes possible the recasting of interpretation data in an orientationally invariant form with a consequent drastic reduction in the number of type curves required for a particular problem.     

THE USE OF OBSERVATIONAL SPACE IN SEISMIC REFRACTION TECHNIQUES *

Attention is given in this paper to the display of intensive seismic refraction information in a convenient form similar to spatial display techniques being developed for resistivity methods. An observational space for first arrivals is defined and illustrated with respect to some simple structures and the possible use of such a representation in diagnosis is discussed. The spatial display is suitable both for steeply dipping and gently dipping structures. In the latter case, the low relief space may be subjected to further operations to produce apparent velocity distributions and values simply related to plus times. A practical example of the latter process and the subsequent interpretation is given.