Statics Applied To Shallow Seismic Reflection Data

The proper handling of static corrections is an issue that is of critical importance to shallow<br>seismic reflection surveys because of the high frequencies used, the large velocity variations that<br>frequently exist in the near surface, and the shallow depths of investigation. The adaptation of<br>conventional methods of determining static corrections is often inadequate for shallow seismic<br>reflection data. This paper presents a method of handling static corrections which addresses the<br>problem in terms of long-, medium-, and short-wavelength variations in topography and nearsurface<br>velocity variations. An analysis of first-arrival data at intervals along the survey line is<br>used to estimate a layered, near-surface, velocity structure. First-break picking is then used to<br>align the first arrivals to a laterally-interpolated, near-surface, velocity function. This process<br>corrects for medium- (i.e. within spread length), and long-wavelength (>spread length), nearsurface<br>velocity variations, as well as most of the static contributions related to individual<br>geophone locations and elevations (i.e. short-wavelength corrections). Accurate residual statics<br>correct any remaining short-wavelength errors. Finally, topographic variations (longwavelength)<br>are corrected post-stack. Both model results and application of this method to actual<br>shallow seismic reflection data show this to be a robust and effective method of correcting for<br>statics.