摘要:

AbstractBy using two components of anomalous magnetic fields and a formulation including complex numbers it is possible to calculate the position parameters of thick plates and both magnetization and position of thin plates directly from any two or three points of anomaly profiles. The formulae (interpretation operators) allow automatic topographic corrections to be made. The new two‐component operators give more reliable results than the conventional methods of interpretation. The variance of the parameter values obtained with subsequent points of an anomaly measures directly, the total error of interpretation.The application of infinite thin plate operators to a long profile results in characteristic patterns, from which the estimation of the number of plates and their approximate position is possibl

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1976.tb00381.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

AbstractResults of a gravity survey conducted over Raniganj coalfield, one of the Gondwana basins of Damodar Valley in north‐eastern part of India, are presented. The gravity field was separated into regional and residual components. The residual Bouguer anomaly map shows that the coalfield is characterized by a gravity low of about—32 mGal associated with Gondwana sediments. The deepest part of basin is found to be located near Asansole (23° 40’N, 86° 55’E), where the maximum thickness of sediments is estimated to be about 1.3 miles (2.08 km). The faults along the northern as well as the southern boundaries are found to be normal. The Gondwana sediments appear to continue eastward beneath alluvium and laterite of Bengal basin as far as

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1976.tb00382.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

AbstractAn analysis is made of the propagation of the measuring error in the different stages of the interpretation by the linear filter and reducing method.This analysis leads to an understanding of the range of possible values of the layer parameters and of the nature of the relation between them.It is shown that this relation is not always adequately described by the equivalence expressions of Maillet.

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1976.tb00383.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

AbstractNone of the processes of estimation currently available is fully acceptable to the geophysicist. Firstly, they all assume that the variable, be it seismic reflection time, rms velocities, Bouguer anomaly, etc.… is random, amenable to pure statistical considerations, and the processes all disregard the relationships which link the values of the variable in the different points of the domain under investigation. Secondly, they do not provide the geophysicist with any guideline for smoothing his data, as smoothing and estimation are considered two separate operations. Thirdly, they fail to offer a valid criterion of estimation and a measure of the estimation error.The krigeage process overcomes the above mentioned difficulties. It synthesizes the structural or “geostatistical’ characteristics of the variable by using a function called the variogram (variances of the increases of the variable with respect to distance and direction). It smoothes the variable, when necessary, as a function of the “nugget effect’ (value at the origin of the experimental variogram). It yields an optimum estimation of the variable by minimizing the estimation error, and it computes a measure of the reliability of the estimation, the variance of krigeage.The process is demonstrated herein with three examples of variograms on seismic and gravity data and an example of contouring of velocities, reflection times and depths of a productive layer in an oil field, with detection and correction of irregular data, smoothing of velocities, migration of depth points, and display of estimat

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1976.tb00384.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

AbstractA new scheme for continuing aeromagnetic data along a profile with constantly changing elevation to a horizontal level is presented in this paper. It only requires some modifications of the conventional methods which are designed to continue potential field data from one horizontal level to another level.The new scheme procedes in the following steps: (1) digitization of anomaly along flight level, thus giving distance and elevation to the desired horizontal level at each station. (2) upward continuation at each digitized point from the corresponding elevation to a desired horizontal level. The validity and usefulness of the scheme is shown with theoretical and real data.

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1976.tb00385.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

AbstractAn offshore self‐potential array, towed behind a small boat, has recorded anomalies of up to −300 mV. These anomalies were related to conductive onshore deposits, and appear to be caused by offshore extensions of the deposits. Along with locating onshore deposits and their offshore extensions, the system may be useful for locating offshore deposits with no onshore extension. The background noise level of the system typically is a few tenths of a millivolt, allowing reliable recording of one millivolt gradient anomalies under average sea conditi

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1976.tb00386.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

AbstractIt is well known that interval velocities can be determined from common‐reflection‐point moveout times. However, the mathematics becomes complicated in the general case ofnhomogeneous layers with curved interfaces dipping in three dimensions.In this paper the problem is solved by mathematical induction using the second power terms only of the Taylor series which represents the moveout time as a function of the coordinate differences between shot and geophone points. Moreover, the zero‐offset reflection times of thenth interface in a certain area surrounding the point of interest have to be known. Then—I upper interfaces and interval velocities are known too on account of the mathematical induction method applied. Thus, the zero‐offset reflection raypath of thenth interface can be supposed to be known down to the intersection with the (n—1)th interface.The method applied consists mainly in transforming the second power terms of the moveout time from one interface to the next one. This is accomplished by matrix algebra.Some special cases are discussed as e.g. uniform strike and small

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1976.tb00387.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

AbstractThe solution for the potential distribution about a point source of current placed at the surface of a continuous half‐space is obtained for two cases: (1) the resistivity increases linearly with depth; (2) the conductivity increases linearly with depth. In each case, an expression for the apparent resistivity is established and master curves are presented for both the Wenner and the Schlumberger configurations. The results can be used in the interpretation of electrical sounding data in specified geologic situations. Furthermore, they may be used as a first step in the development of solutions for the more complex electric sounding problem

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1976.tb00388.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

AbstractThis paper is an experimental extension of the theoretical investigations by Roy (1975) on the relative performances of the Laterolog 7, normal and some other sondes in logging of resistive formations. Only infinitely resistive formations have been simulated and placed in a tank containing tap water (true resistivity 27 Ωm) as electrolyte—representing both the mud column and the adjacent formations.Two sets of laboratory results (Doll 1951, NN 1958, 1969), have been repeated and we find that, for both these sets, the performance of the normal device is by far the superior of the two. In addition, we have studied the effect of varying the spacingsA1A2,O1O2andAMof Laterolog 7, normal, and two new sondes—Laterolog 4 and modified unipole—for two bore hole diameters in each case. For formation thicknesses less thanA1A2orAM, the Laterolog 7 is unsuitable because its response is flat and close to the base‐line value. The normal device is more diagnostic, although, in such a case, it registers a trough or a resistivity low even against a resistive formation.For bed thicknesses clearly greater thanA1A2orAM, the normal sonde is decidedly superior to Laterolog 7, since its anomalies are sharper and larger. When the formation thickness is equal to or only slightly larger thanA1A2orAM, Laterolog 7 is somewhat better as it records a readable positive deflection while the normal does not. However, one must remember that a single run of the conventional resistivity log includes two normals and a lateral at different spacings. Laterolog 4 and modified unipole can in many instances produce better logs than normal, other considerations apart.The results are consistent with our own theoretical predictions and experience in surface resistivity profiling. They do not, however, agree with the prevalent concepts on Laterolog 7 vis‐a‐vis

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1976.tb00389.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

AbstractThe least squares estimation procedures used in different disciplines can be classified in four categories:a. Wiener filtering,b. b. Autoregressive estimation,c. c. Kalman filtering,d. d. Recursive least squares estimation.The recursive least squares estimator is the time average form of the Kalman filter. Likewise, the autoregressive estimator is the time average form of the Wiener filter. Both the Kalman and the Wiener filters use ensemble averages and can basically be constructed without having a particular measurement realisation available.It follows that seismic deconvolution should be based either on autoregression theory or on recursive least squares estimation theory rather than on the normally used Wiener or Kalman theory. A consequence of this change is the need to apply significance tests on the filter coefficients.The recursive least squares estimation theory is particularly suitable for solving the time variant deconvolution

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1976.tb00390.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY