SUMMARY An efficient algorithm of the network shortest path calculation of rays and traveltimes of the first arrivals is described. The traveltime error of such computations is estimated. The rough estimate of the relative traveltime error is evaluated locally at all network nodes prior to network ray tracing, and is minimized by means of a proper choice of the sizes of forward stars. In this way, the structure of the network is adjusted for a particular model and for a particular computer memory. After network ray tracing, the error estimate is refined and the absolute error bounds of the calculated traveltimes are evaluated. The method and its accuracy are demonstrated on numerical examples.

3-D network ray tracing

Summary. Several important applications of the paraxial ray approximation (PRA) to numerical modelling of high-frequency seismic body wavefields are discussed. The PRA can be used to evaluate the displacement vector not only directly on the ray, as in the standard ray method. but also approximately in the vicinity of this ray. The PRA also offers simple ways of approximate evaluation of paraxial rays, situated in the vicinity of the central ray, and of two-point ray tracing. A very important application of the PRA consists in a simple, fast and effective Computation of body-wave synthetic seismograms in general, 3-D, laterally inhomogeneous, layered structures. Examples of synthetic seismograms for 3-D structures, computed using the PRA, are presented.

Paraxial ray approximations in the computation of seismic wavefields in inhomogeneous media

The seismic ray method has found broad applications in the numerical calculation of seismic wavefields in complex 3-D, isotropic and anisotropic, laterally varying layered structures and in the solution of forward and inverse problems of seismology and seismic exploration for oil. This chapter outlines the basic features of the seismic ray method, and reviews its possibilities and recent extensions. Considerable attention is devoted to ray tracing and dynamic ray tracing of S waves in heterogeneous anisotropic media, to the coupling ray theory for S waves in such media, to the summation of Gaussian beams and packets, and to the selection of models suitable for ray tracing.

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Seismic ray method: Recent developments

The paper outlines the most important results of the paraxial complex geometrical optics (CGO) in respect to Gaussian beams diffraction in the smooth inhomogeneous media and discusses interrelations between CGO and other asymptotic methods, which reduce the problem of Gaussian beam diffraction to the solution of ordinary differential equations, namely: (i) Babich’s method, which deals with the abridged parabolic equation and describes diffraction of the Gaussian beams; (ii) complex form of the dynamic ray tracing method, which generalizes paraxial ray approximation on Gaussian beams and (iii) paraxial WKB approximation by Pereverzev, which gives the results, quite close to those of Babich’s method. For Gaussian beams all the methods under consideration lead to the similar ordinary differential equations, which are complex-valued nonlinear Riccati equation and related system of complex-valued linear equations of paraxial ray approximation. It is pointed out that Babich’s method provides diffraction substantiation both for the paraxial CGO and for complex-valued dynamic ray tracing method. It is emphasized also that the latter two methods are conceptually equivalent to each other, operate with the equivalent equations and in fact are twins, though they differ by names. The paper illustrates abilities of the paraxial CGO method by two available analytical solutions: Gaussian beam diffraction in the homogeneous and in the lens-like media, and by the numerical example: Gaussian beam reflection from a plane-layered medium.

Gaussian beams in inhomogeneous media: A review

An integral expansion which expresses a plane monochromatic wave as a superposition of Gaussian beams is found. The expansion can be used to solve many wave propagation problems in complicated structures, including laterally inhomogeneous media with curved interfaces.

Expansion of a Plane Wave into Gaussian Beams

A system of three ordinary non-linear first order differential equations is proposed for the computation of the geometrical spreading of the wave front of a seismic body wave in a three-dimensional medium. The variables of the system are the parameters which provide a second order approximation of the wave front.

A wave-front curvature approach to computing ray amplitudes in inhomogeneous media with curved interfaces

Among the various dynamic ray tracing systems described by Cervený and Hron[1] is one particular linear system of second order that readily provides identical parameters (in the ray centred coordinate system) to those that fall out of the system by Popov and Psencik[3, 4]. Hence the initial conditions of the latter system for sources and interfaces can easily be used to provide those for the linear system of second order.

On dynamic ray tracing in three dimensional inhomogeneous media

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A wave-front curvature approach to computing ray amplitudes in inhomogeneous media with curved interfaces

On dynamic ray tracing in three dimensional inhomogeneous media