by J. Gazdag, G. Radicati, P. Sguazzero, H.-H. Wang
Seismic prospecting aims at determining the structure of the earth from indirect measurements. Acoustic wave fields are generated at the surface, penetrate the earth, and are backscattered by the earth's inhomogeneities. The data recorded at the surface are processed in a complex sequence of steps among which seismic migration plays an important role. This is a wave depropagation process that permits the localization in depth of the origin of the diffraction events measured (in time) at the surface. This paper presents an overview of the major wave-equation migration methods. The most frequently executed algorithms or kernels on which the execution speed depends most crucially are given particular attention. The speedup resulting from scalar-to-vector formulation is presented over wide ranges of dimensionality for linear tridiagonal equation solvers, Fourier Transforms, and convolution operations. The vectorizability and resulting speedup are also addressed in the case of migration schemes known as the Phase-Shift Method and the Phase Shift Plus Interpolation (PSPI) Method. It is shown that Fourier domain migration based on the phase-shift concept lends itself conveniently to multilevel parallelism on the 3090 Vector Facility (VF): vectorization of the innermost loops and concurrent processing in the outer loops by means of the VS FORTRAN Version 2 Multitasking Facility.