固物研究生论坛 -Long-wavelength statics solutions for the near surface

The complexity in the near surface area can significantly affect land seismic data processing. If the near surface structures include a thin high-velocity layer above a weathering layer on top of the high-velocity bedrock, the first arrivals of a shot gather may exhibit a shingling pattern, where the first arrivals associated with the high-velocity layer are visible only within the near offset, and the bedrock refraction becomes a dominant arrival at the far offset. When this velocity reversal occurs, the effectiveness of conventional first-arrival traveltime tomography is limited. Nevertheless, the later refraction arrivals still contain substantial information about the weathering layer and the long-wavelength statics. In this study, we tested three different methods for statics and near surface velocity model estimation: the delay-time, generalized linear inversion (GLI), and combined traveltime tomography and refraction traveltime migration method using various synthetic models. Our goal is to assess the effectiveness of these methods in the areas with near surface velocity reversal. The test results suggest all three methods can recover reasonable statics solutions if the shallow velocity layers are simple and relatively flat. For more complex models with an undulated near surface high-velocity layer with variable thickness, better long-wavelength statics solutions are produced by the combined traveltime tomography and refraction traveltime migration method. In all tests, none of the derived near surface velocity models are entirely satisfactory. Nevertheless, the models derived from the combined traveltime tomography and refraction traveltime migration method are better and bear more resemblance to the true velocity model than the delay-time and GLI methods.