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Composite Refraction-Reflection Stack Sections: Imaging Shallow Subsurface Features
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, 8th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems, Apr 1995, cp-206-00100
Abstract
Seismic data sets are gcncrally processed to intcrprct subsurface features using either refracted or reflected<br>arrivals, but not both. In processing seismic reflection data, refracted arrivals are commonly discarded<br>and considered to hc noise during the early stages of the processing flow. This paper addresses a<br>seismic data processing scheme that utilizes both reflected and refracted arrivals simultaneously to image<br>shallow subsurface geologic features. In addition to conventional reflection stack sections, refraction stack<br>sections are protluccd using split-spread and/or off-end data after applying a linear-moveout correction that<br>adjusts the refraction arrival times into modified intercept (delay) times that correspond to the related reflection<br>times. Velocities necessary for the adjustment arc obtained from constant-velocity display panels<br>that arc generated on the basis of the linear-movcout correction for the refracted first and later arrivals. It<br>is shown that the velocity obtainrd from the test panels is the actual velocity of a subhorizontal refractor<br>in which the critically refracted waves travel. In the case of a dipping refractor, the velocity obtained is an<br>apparent velocity. ‘I‘he refraction stacks produce cxtrcmcly good refracted signals representing horizons that<br>can be correlated with corresponding reflections and/or synthetic seismograms from well log data. This<br>correlation forms the justification for constructing composite refraction-reflection stack sections by combining<br>the reflection and refraction arrivals in common midpoint gathers. This procedure minimizes loss<br>of seismic data and yields composite refraction and rcflcction stack sections that recover additional images<br>of shallow subsurface features.