摘要:

ABSTRACTHigh resolution seismic reflection exploration for minerals places severe demands on field practice so as to maximize the signal‐to‐noise bandwidth. In particular, all horizontally propagating coherent noise, especially ground roll, must be attenuated.The blocking effect of a trench between source and receiver has been investigated by means of two‐dimensional physical seismic model experiments. Rectangular, circular and wedge‐shaped saw‐cuts of various dimensions were studied. The results show that thin rectangular cuts of depth equal to one‐quarter of the Rayleigh wave noise wavelength produce a 12 dB or better improvement in the signal‐to‐noise ratio. Rayleigh wave attenuation is greater than 30 dB at a cut depth of one wavelength. In the field applications envisaged, this corresponds to trenches up to a few metres deep. The trenches should be filled with foam or loose sand to dampen out mode conversion and diffraction noise. There are obvious practical difficulties of implementing such a technique in routine CMP operations.The technical effectiveness of the saw‐cut is illustrated by imaging a deeply‐buried small hole (diffractor) in an aluminium plate. Without the saw‐cut between source and receiver, the seismic record is dominated by Rayleigh wave noise, masking P‐wave arrivals from the target diffractor. However, with a saw‐cut of depth three‐quarters of a Rayleigh wave wavelength, the improvement is dramatic, making it easy to detect and identify the hole. When scaled to the field situation, this is equivalent to imaging a 6 m tunnel at a depth of 400 m, using a surface trench of dep

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1989.tb02224.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

ABSTRACTThe use of cables with a large number of closely spaced receivers has become increasingly common in marine seismic acquisition; this gives geophysicists the opportunity to improve data quality in processing centres. In particular, arrays need not be fixed in the field, but instead can be flexibly simulated in the computer.The paper defines a strategy to optimize the application of receiver‐array simulation, based on the requirement that signal resolution should not be compromised. The approach consists in the design ofk‐domain filters through the use of Chebyshev polynomials that define the spatial response of the desired array, with array length that varies with time according to spatial and vertical resolution constraints set by the interpreter.An example, taken from a marine 240‐channel seismic line, ties the underlying ideas to practical application and shows that appropriate array processes can contribute to improving the quality of seismic data, especially in areas with complex geology and strong coherent

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1989.tb02225.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

ABSTRACTDEKORP 2‐S is the first profile carried out in the German continental reflection seismic programme. Besides numerous reflections in the lower crust, the seismic section is characterized by strongly curved events that are interpreted as diffractions. These diffractions occur as clusters, mainly in two areas of the profile: the Dinkelsbühl and the Spessart area. This paper deals with the Dinkelsbühl diffractions where three‐dimensional control is available. The control is provided by two additional profiles P‐1 and Q‐40 which run parallel and perpendicular to the main line, DEKORP 2‐S. The type and the location of the diffractors are determined by traveltime‐modelling using crustal velocity functions derived from in‐line wide‐angle observations. A model with inclined line diffractors provides the best fit to the data for all three profiles. Projections of these line diffractors to the surface show that they are aligned parallel to the strike direction of the Variscides. This suggests that the diffractions are associated with the suture zone between the Saxothuringian and Moldanubian geo

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1989.tb02226.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

ABSTRACTAn accurate, fast, and simple algorithm for 3D modelling of seismic edge diffractions is presented. It is based on a generalized Kirchhoff theory that applies also to inhomogeneous (non‐uniform) media. Both the boundary values and the Green functions in the Kirchhoff diffraction integral are determined by dynamic ray tracing, and each ray event is treated separately to obtain a description with clear physical interpretation. For each event the resulting Kirchhoff diffraction integral is evaluated by means of a uniform asymptotic technique that remains valid for receiver points near shadow boundaries. Since all parameters needed in the computations are obtained from dynamic ray tracing, the algorithm can readily be incorporated in existing software packages for 3D seismic ray modellin

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1989.tb02227.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

ABSTRACTTwo geophysical methods [resistivity soundings and spontaneous potentials (SP)] are used to investigate aquifers in the Quaternary volcanic formations of the Chaîne des Puys (France). The interpretation of the resistivity soundings required a specific work of determination of the resistivity of the formations concerned. The basement topography, characterized by axial horst and graben structures and perpendicular palaeovalleys, was revealed. SP was developed experimentally in the field and theoretically. It is shown that the SP anomalies can be considered as double‐layer potentials, with their source on the aquifers' interfaces. The most significant of them is the water table, which creates an SP anomaly of similar but inverted form. SP anomalies due to flows in unconfined aquifers, in palaeovalleys, and in volcanic ranges are computed and compared with the observed ones. These two methods have determined the extent and the boundary conditions of the different hydrogeological basins and have determined the major drainage axes and the groundwater flow patte

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1989.tb02228.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractThe inverse problem of magnetotellurics over a horizontally stratified earth is described, with emphasis on practical application. The inversion is divided into basically two steps. The construction of some best solution, and the analysis of that solution with regard to uncertainty and complexity. For the construction of best solutions a robust non‐linear solver was developed, and for the estimation of parameter errors a modified eigenvalue‐eigenvector analysis is performed to better describe non‐linear effects. The choice of the number of layers is shown to be intimately connected with the structure of data errors and the misfit between model and data. An example from the Siljan impact structure in Sweden illustrates the power of the tech

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1989.tb02229.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

ABSTRACTThe analytical solution, for the H‐polarization magnetotelluric impedance, of a series of multiple, vertical, conducting slabs (dikes) embedded in a host medium is extended to an infinite array in order to model an anisotropic layer. The solution is used to study the effects of such strongly anisotropic media on the surface impedance. At low frequencies such vertically laminated structures behave as a bulk material. It is shown that the effective bulk parameters are those expected from d.c. theory. However, practical electrode separations may not be long enough or adequately positioned to correctly obtain these bulk parameters from the measured impedance. Thus, such structures can masquerade as quite different one‐dimensional structures. A haphazard use of long electrode spacings will not necessarily produce correct resu

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1989.tb02230.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY