摘要:

ABSTRACTPoint source reflection/transmission responses from planar interfaces based on the Sommerfeld‐Weyl integral are causal and are given in the form of a solution integral with an infinite integration limit. They can be simply transformed to integrals with a finite limit by an approach that takes into account causality as well as time‐symmetry aspects. To introduce the fundamental principles involved, the transformation is applied to the simple case of a point‐source response from a planar acoustic interface. For a point source above a planar interface separating an upper and lower acoustic half‐space of velocityc1andc2the inhomogeneous plane waves in the Sommerfeld‐Weyl source representation do not contribute to the final result ifc1≤c2and only a limited spectrum of inhomogeneous plane waves comes into

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1986.tb00449.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

ABSTRACTData from routine seismic surveys contain considerable information about the geo‐acoustic properties of the seafloor. Waves are reflected at a wide range of angles of incidence from near‐vertical reflections (higher multiples) to supercritical reflections (primary and lower multiples). The reflection coefficient is approximately constant for small angles of incidence (<10°) but varies greatly for larger angles of incidence. Near‐vertical reflections are used to determine the seafloor density. The P‐velocity in the seafloor is determined in advance from the critical distance using the amplitude variation of the primary as well as the multiples. TheVp/VSratio is determined by modeling the amplitude variation with the angle of incidence. The primary reflection from the seafloor and the first three multiples are included in the modeling.Seismic data obtained with both conventional and superlong airgun arrays have been modeled. Data collected from the Barents Sea show that even if the P‐velocity is the same at different sites, theVp/Vsratio, density and Poisson's ratio vary significantly. The most extreme example shows that for a P‐velocity of 2.80 km/s theVp/Vsratio varies between 1.9 and 6.0. The corresponding densities vary from 2.36 g/cm3to 1.80 g/cm3and the Poisson's ratio varies from 0.31 to 0.49.The acoustic modeling offers a method of assessing the mean geotechnical or mechanical properties of larger volumes of marine sediments in terms of incompressibility, shear modulus and Poi

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1986.tb00450.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractAn experimental cross‐hole and face‐to‐borehole in‐seam seismic survey was carried out at Invincible Colliery in the Western Coalfield of New South Wales. Objectives were to determine propagation characteristics of the Lithgow seam and to establish the infrastructure for seismic mapping hole‐to‐hole in Australia.The seam supports leaky P‐, S‐ and P‐SV‐modes. These modes propagate with group velocities (at 60 Hz) of 3.1, 1.5 and 1.2 km/s respectively. Particle motion polarization is well developed, as is dispersion of the SH‐mode. Attenuation rates are high. The seam is lossy (Qof approximately 20). Two prominent structures were mapped by mode conversion. One is believed to be a fracture zone, the other a zone of intense roof thrusting.The old workings and a minor strike‐slip fault, which intersected raypaths, were found to be relatively transparent to P‐ and S‐waves at 60 Hz.Telemetry delay and shot‐break timing errors of the exploder box are significant. The resulting traveltime scatter is reduced by means of a least‐squares “statics” procedure. The group velocity estimation algorithm (based on Fourier transform) yields dispersion characteristics which can be matched with theoretical results for a simple model of a coal seam waveguide.The experiment demonstrates the capability to retrieve in‐seam seismic data of diagnostic quality over an appreciable distance (2 km). The experience gained in both survey layout and data processing will be beneficial to future seam wa

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1986.tb00451.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

ABSTRACTBayesian statistics are applied to the problem of signal‐to‐noise ratio enhancement from a common‐midpoint gather. By maximizing the a posteriori probability distribution of the gather with respect to the minimum‐offset trace and suppressing multiples via a semblance criterion, a statistically biased stack is formed with signal‐to‐noise ratio comparable to that of the usual stack while preserving the resolution and registration of the original noisy trace.Application of the algorithm to real data reveals geologically significant features which are indistinct in the standard stac

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1986.tb00452.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

ABSTRACTHigh‐resolution seismic surveys were performed on an underground gas storage of Gaz de France at Gournay‐sur‐Aronde (Oise) in order to obtain information about gas bubble boundaries within the reservoir. For that purpose, a light seismic source Soursile and spreads with small spacing between geophone groups (10 m) and small geophone group extension (10 m or 20 m) were used. In December 1982, a line recorded on the top of the anticline structure of the gas reservoir provided an estimation of the lateral extension of the bubble based on an amplitude anomaly (dim spot) associated with reservoir seismic horizons. In order to estimate the displacement of the gas bubble within the reservoir, three lines were recorded on the southeastern part of the anticline at different time periods (April 1981 and January 1982) with different volumes of gas in the reservoir. It is assumed that a variation of gas volume introduces a seismic velocity variation and as a result a travel‐time variation for the seismic waves that pass through the reservoir. A method based on the residual time shifts observed on reflectors below the reservoir from one survey to the other was developed and implemented. This method permitted a detection of a movement gas bubble boundary between April 1981 and January 1982 which agrees with drill hole data (water level measur

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1986.tb00453.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

ABSTRACTA number of authors in the exploration literature have written about anisotropy, but have restricted their discussions to wave propagation through rock having transverse isotropy with a vertical symmetry axis. This note shows that there are fundamental differences between transverse isotropy when the symmetry axis is vertical (normal to the free surface) and more general anisotropy with an azimuthal variation of properties. These differences are important now that effective azimuthal shear‐wave anisotropy resulting from aligned cracks and pores is becoming recognized as a significant property of crustal rock

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1986.tb00454.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

ABSTRACTDuring development of theoretical methods to compute synthetic seismograms, a new type of wave called S*‐wave was discovered by Hron and Mikhailenko. This wave propagates with the shear‐wave velocity and can be interpreted as a non‐geometrical wave arrival with large amplitudes strongly depending on the depth of a pure P‐point source.In this first experimental verification of the existence of S*‐waves by means of two‐dimensional model‐seismics it is demonstrated that:1. the S*‐wave exists and depends on the source distance from the free surface; 2. the S*‐wave is generated as an ordinary shear wave on the free surface at the point located directly above the P‐source, as illustrated in the synthetic seismograms. The measured seismograms agree remarkably well wit

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1986.tb00455.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

ABSTRACTA contribution is given to the solution of the problem of filtering noise‐degraded Schlumberger sounding curves. It is shown that the transformation to the pole‐pole system is actually a smoothing operation that filters high‐frequency noise. In the case of residual noise contamination in the transformed pole‐pole curve, it is demonstrated that a subsequent application of a conventional rectangular low‐pass filter, with cut‐off frequency not less than the right‐hand frequency limit of the main message pass‐band, may satisfactorily solve the problem by leaving a pole‐pole curve available for interpretation. An attempt is also made to understand the essential peculiarities of the pole‐pole system as far as penetration depth, resolving power and selectivity

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1986.tb00456.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

ABSTRACTThe basic principles of the application of the linear system theory for smoothing noise‐degraded d.c. geoelectrical sounding curves were recently established by Patella. A field Schlumberger sounding is presented to demonstrate first their application and validity. To achieve this purpose, firstly it is pointed out that the required smoothing or low‐pass filtering can be considered as an intrinsic property of the transformation of original Schlumberger sounding curves into pole‐pole (two‐electrode) curves. Then we sketch a numerical algorithm to perform the transformation, opportunely modified from a known procedure for transforming dipole diagrams into Schlumberger ones. Finally we show a field example with the double aim of demonstrating (i) the high quality of the low‐pass filtering, and (ii) the reliability of the transformed pole‐pole curve as far as quantitative interpretation i

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1986.tb00457.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

ABSTRACTThe resistivity and induced polarization responses due to a number of IP targets for a down‐hole three‐array have been calculated numerically. The IP targets are approximated by triangle‐faceted polyhedra; number and size of the facets are limited by the numerical procedure. Despite this limitation a number of profiles have been obtained for a sphere, lens, prolate spheroid and thin dipping slab. The profiles obtained do not differentiate between the shapes of the IP targets, but depend upon the vertical extent of the target within the search‐radius of the borehole. The type curves produced could be of use for preliminary interpretation and in the field for planning the next stages of a geophysical survey.The lateral and vertical search radii of the borehole are increased by the use of such an array. For the bodies used it is estimated that the search radii are extended by 2.0 dipol

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1986.tb00458.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY