ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1995.tb00121.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractA generalized diffraction tomography algorithm is developed, which in principle can handle irregularly spaced data, curved acquisition lines and non‐uniform background models. By direct comparison with medical diffraction tomography, it is shown that the generalized method involves the same two processing steps: data filtering and back‐propagation. The filter handles the irregular sampling of the model space and the uneven energy coverage, while the back‐propagation operator removes the wave propagation effects. Paraxial ray‐tracing techniques are employed to compute both these quantities.In medical diffraction tomography, the resolution vector (i.e. the Fourier vector of the model space) is defined by the incident and scattered plane‐wave directions. It is shown here that a similar relationship exists for a non‐uniform background, where the resolution vector at a particular image point is defined by the incident and scattered ray directions. Consequently, the impulse response of the generalized algorithm becomes space variant.Finally, a general processing procedure for transmission mode seismic data, based on this generalized algorithm, is proposed. The potential of the method is demonstrated using synthetic cros

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1995.tb00122.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractVarious applications of a new geophysical reconstruction method, generalized acoustical diffraction tomography (GADT), which is based on transmission data as input are considered. Conventional diffraction tomography methods normally require linearization with respect to a uniform reference medium and regular sampling along a straight line. Thus, these methods will not work well when the background is strongly non‐uniform and/or the acquisition geometry is arbitrary. However, GADT can, in principle, handle both irregularly spaced data, curved acquisition lines, and non‐uniform background models.A number of controlled model tank and field experiments, where the model and the test object(s) are known a priori, have been carried out. After acquiring the tomographic data in each experiment, these are used to compute a reconstruction of the model, which can then be compared with the actual, known model. The method's ability to yield high‐quality images of the different targets is demonst

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1995.tb00123.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractA new method of numerical computation of elastic wavefields in regions containing caustics is tested. The method is an extension of the asymptotic ray theory (ART). The essential features of the method consist of the application of expressions which are well defined at caustics and expressed in terms of ray tracing combined with complex ray tracing in caustic shadows. The method and an outline of the underlying theory are briefly presented, followed by a comparison with finite differences on a test model involving a caustic cusp. The comparison reveals the unexpectedly high degree of accuracy of the new method.

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1995.tb00124.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThe Belvedere Spinello salt mine is located in the Catanzaro Province of Calabria in Southern Italy. An extensive mining program has caused the development of Underground cavities filled with brine and the migration of this brine has been of great environmental concern to the mine owners. This paper presents the results of a multidimensional interpretation of a two‐phase resistivity and magnetotelluric (MT) survey that was performed in an attempt to determine the complex conductivity structure of the mine area and to gain information on brine development and migration pathways. Key resistivity soundings were interpreted using a 2.5D algorithm based on the Polozhii decomposition method. The MT data were interpreted using a 2D finite‐element code. A conductivity model was developed, integrating available geological and drill‐hole information. The interpretation of the MT data, collected five years after the acquisition of the resistivity data, shows a conductive feature of depth that is not resolved in the resistivity interpretation. This feature has been interpreted as a thick brine zone that has developed as a result of mining during the interval between the resistivity and the MT measure

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1995.tb00125.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractNone of the standard porosity‐velocity models (e.g. the time‐average equation, Raymer's equations) is satisfactory for interpreting well‐logging data over a broad depth range. Clays in the section are the usual source of the difficulty through the bias and scatter that they introduce into the relationship between porosity and P‐wave transit time. Because clays are composed of fine sheet‐like particles, they normally form pores with much smaller aspect ratios than those associated with sand grains. This difference in pore geometry provides the key to obtaining more consistent resistivity and sonic log interpretations.A velocity model for Clay–sand mixtures has been developed in terms of the Kuster and Toksöz, effective medium and Gassmann theories. In this model, the total pore space is assumed to consist of two parts: (1) pores associated with sand grains and (2) pores associated with clays (including bound water). The essential feature of the model is the assumption that the geometry of pores associated with sand grains is significantly different from that associated with clays. Because of this, porosity in shales affects elastic compliance differently from porosity in sand‐Stones. The predictive power of the model is demonstrated by the agreement between its predictions and laboratory measurements and by its ability to predict sonic logs from other logs over large depth intervals where formations vary from unconsolidated to consolidated sandsto

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1995.tb00126.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstracrAn amplitude‐preserving migration aims at imaging compressional primary (zero‐or) non‐zero‐offset reflections into 3D time or depth‐migrated reflections so that the migrated wavefield amplitudes are a measure of angle‐dependent reflection coeffcients. The principal objective is the removal of the geometrical‐spreading factor of the primary reflections. Various migration/inversion algorithms involving weighted diffraction stacks proposed recently are based on Born or Kirchhoff approximations. Here, a 3D Kirchhoff‐type zero‐offset migration approach, also known as a diffraction‐stack migration, is implemented in the form of a time migration. The primary reflections of the wavefield to be imaged are describeda prioriby the zero‐order ray approximation. The aim of removing the geometrical‐ spreading loss can, in the zero‐offset case, be achieved by not applying weights to the data before stacking them. This case alone has been implemented in this work. Application of the method to 3D synthetic zero‐offset data proves that an amplitude‐preserving migration can be performed in this way. Various numerical aspects of the true‐amplitude zero

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1995.tb00127.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY