Near Surface Modelling by Interactive Refraction Analysis

Abstract

An accurate estimate of the shallow near surface structure, and the static corrections for its compensation, has become more important as seismic exploration objectives become more difficult to attain. The static correction profile must be 'broadband' in the sense of containing good estimates of short, medium, and long wavelength components. In most modern seismic surveying, the short wavelength components (up to one spreadlength), which affect the signal-to-noise ratio of the stacked section, are usually determined by an automatic residual static analysis of the refraction data; while the long wavelengths (greater than about five spreadlengths), which affect structures and velocity estimates, are estimated from uphole survey information. This leaves the medium wavelengths, which also affect structures and velocity estimates: these cannot be reliably estimated from the reflection data, and would require an uphole survey spacing of half a spreadlength for complete resolution ? an expensive proposition.