摘要:

AbstractOne of the basic parameters of the rock formation surrounding a fluid‐filled borehole to be estimated is the shear‐wave velocity. In the present contribution a novel method for carrying out this estimate, based on the use of linear prediction techniques, is proposed. It is assumed that the shape and energy content of each wave can be accurately modelled by an ARMA (Auto Regressive Moving Average) impulsive process and by an appropriate delay. The overall seismogram is then considered to be a multiple impulsive ARMA process and the estimation is carried out by using the residual at the output of an extended version of the Burg lattice predictor. The resulting algorithm is very effective as illustrated by several examples performed on synthetic and real seismogr

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1990.tb01856.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractThe pioneering work of E. T. Jaynes in the field of Bayesian/Maximum Entropy methods has been successfully explored in a number of disciplines. The principle of maximum entropy (PME) is remarkably powerful and versatile and leads to results which are devoid of spurious structure. Minimum relative entropy (MRE) is a method which has all the important attributes of the maximum‐entropy (ME) approach with the advantage that prior information may be easily included. These ‘soft’ prior constraints play a fundamental role in the solution of underdetermined problems. The MRE approach, like ME, has achieved considerable success in the field of spectral analysis where the spectrum is estimated from incomplete autocorrelations. In this paper we apply the MRE philosophy to 1D inverse problems where the model is not necessarily positive, and thus we show that MRE is a general method of tackling linear, underdetermined, inverse problems. We illustrate our discussion with examples which deal with the famous die problem introduced by Jaynes, the question of aliasing, determination of interval velocities from stacking velocities and, finally, the universal problem of band‐limited extrapolation. It is found that the MRE solution for the interval velocities, when a uniform prior velocity is assumed, is exactly the Dix formulation which is generally used in the seismic i

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1990.tb01857.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractRecent years have seen an increasing need for high‐precision gravity meters. A widely used and the most accurate one is the LaCoste‐Romberg, model D (LCR‐D) meter, equipped with electronic readout. According to the manual the reading accuracy is 5 μGal. A way of reducing most of the instrumental factors limiting the accuracy is the use of an electronic feedback system.We have fitted the LCR‐D 34 with a Schnüll‐Röder‐Wenzel, model D (SRW‐D) feedback. After installation the readout voltage was calibrated, the instrumental behaviour tested, and the accuracy of the system determined. By repeat readings in the laboratory without moving the meter, the standard deviation for a single reading is better than 4 μGal in normal mode and better than 1 μGal in feedback mode. The accuracy of gravity differences ‐ this is usually observed in field practice ‐ is the mean value of the repeat errors of several sets of differences observed in a short time to avoid any corrections. This accuracy is better than 9 μGal in normal mode and better than 5 μGal in feedback mode. With this, the accuracy of a single reading becomes more than 6 μGal and more than 3 μGal, respectively.As the described improvement of accuracy was found to be not as good as expected, additional improvements should centre on the use of electronic levels instead o

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1990.tb01858.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractA fundamental step in the solution of most non‐linear inverse problems is to establish a relationship between changes in a proposed model and resulting changes in the forward modelled data. Once this relationship has been established, it becomes possible to refine an initial model to obtain an improved fit to the observed data. In a linearized analysis, the Fréchet derivative is the connecting link between changes in the model and changes in the data. In some simple cases an analytic expression for the Fréchet derivative may be derived. In this paper we present three techniques to accomplish this and illustrate them by computing the Fréchet derivative for the ID resistivity problem. For more complicated problems, where it is not possible to obtain an expression for the Fréchet derivative, it is necessary to parameterize the model and solve numerically for the sensitivities ‐ partial derivatives of the data with respect to model parameters. The standard perturbation method for computing first‐order sensitivities is discussed and compared to the more efficient sensitivity‐equation and adjoint‐equation methods. Extensions to allow for the calculation of higher order, directional and objective function sensitivities are also presented. Finally, the application of these various techniques is illustrated for both the 1D and 2D resisti

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1990.tb01859.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractGeoelectrical sounding profiles were collected on the southern part of the Fraser River delta, to provide a geophysical estimate of the subsurface structure and geotechnical properties. The differences between emergent and intertidal areas were assessed, and the geoelectric technique was found to be a viable one in an intermittently exposed tidal‐flat environment. The subsurface geoelectric structure provides a link between reflection seismic data sets for Georgia Strait and the lower mainland. The survey was intentionally designed to complement the conventional exploration information for this basin and the shallow high‐resolution seismic and drilling which focused on the unconsolidated Quaternary section. The electrical models consist of three layers: (I) electrically‐conductive, porous, saturated and under‐saturated marine silts, sands and gravels, overlying (II) less conductive and more consolidated marine clays, and variably reworked glaciomarine deposits together with weathered clastic sedimentary bedrock, which in turn overlies (III) less porous, more resistive, relatively unweathered bedrock. Estimates of thickness and geotechnical properties are obtained for shallow layers which are not available from either the short boreholes or shallow high‐resolution seismic lines. This information is particularly useful in appraising the liquefaction potential of the unconsolidated layers due to earthq

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1990.tb01860.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractIn the linear digital filter theory for calculation of Hankel transforms it is possible to find explicit series expansions for the filter coefficients. A method is presented for optimizing the Hankel filters calculated in this way. For a certain desired accuracy of computation, the sampling density and filter length are minimized by choosing the parameters determining the filter characteristics according to the analytical properties of the input function. A new approach to the calculation of the filter coefficients has been developed for these optimized filters. The length of the filters may be further reduced by introducing a shift in the sampling scheme.

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1990.tb01861.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1990.tb01862.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1990.tb01863.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY