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Analysis of a seismic record in the frequency-wavenumber domain

Ismal M. A.

Acta Geophysica Polonica

1998

Vol. 46, nr 3

325-350

Multi-domain frequency-wavenumber (F-K) filtering has been developed to reduce the complex coherent noise and to solve problems inherent in the application of F-K filtering to down-dipseismic data that can occur in both land and marine data. The noises can be classified into coherent and uncoherent, multiples, ground roll and acoustic waves. The Fast Fourier Transform (FFT) is used two times to segregate a seismic record into two different half planes of frequency-wavenumber space (F-K) on the travelling direction of the events. The computation of both forward and inverse 2-D FFT is done to eliminate the unwanted waves. The F-K plots are periodic in both F and K with filters that are symmetric with respect to K only, in wchich the 2-D F-K spectrum is folded about the F-axis. Apparent-velocity filters can also be designed to remove a noise wedge rather than to pass a signal wedge, with a filter called 'butterfly'. For ideal processing, fine spatial sampling during the original recording is required. The aliasing noise is obviously clearer at shallower depths than deeper and at nearer offsets than at father ones. This technique is appplied to separate the upgoing and downgoig events of the Vertical Seismic Profiling (VSP), wanted and unwanted events of the VSP and surface seismics, and to enhance the signal-to-high velocity noise ratio. Three field examples were selected from varying locations to explain how the F-K processing ma be used.