A Kosloff/Baysal method, 3D migration program implemented on the CYBER 205 supercomputer



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Conventional finite-difference migration has relied on approximations to the acoustic wave equation which allow energy to propagate only downwards. Although generally reliable, such approaches usually do not yield an accurate migration for geological structures with strong lateral velocity variations or with steeply dipping reflectors. An earlier study by D. Kosloff and E. Baysal examined an alternative approach based on the full acoustic wave equation. The 2D, Fourier-type algorithm, which was developed by Kosloff and Baysal, was tested against synthetic data and against physical model data. The results indicated that such a scheme gives accurate migration for complicated structures. This thesis describes the development and testing of a vectorized, 3D migration program for the CYBER 205 using the Kosloff/Baysal method. The program can accept as many as 65,536 zero-offset (stacked) traces. In order to efficiently process a data cube of such magnitude (65 million data values), data motion aspects of the program employ the CDC supplied subroutine, SLICE4. SLICE4 provides high speed input/output, taking advantage of the CDC Q7BUFIN and Q7BUF0UT routines and of the parallelism achievable by distributing data transfer over four input/output channels. The results obtained are consistent with those of Kosloff and Baysal. These results, viewed from the perspective of an accurate, 3D, variable velocity migration technique, appear to justify additional investigations, building upon the work reported in this thesis.



CYBER computer, Fourier transformations