Prestack Depth Migration of Deep Reflection Data at Chinese Continental Scientific Drilling Site

Application of prestack depth migration methods has some difficulties owing to low signal‐to‐noise ratio and wide recording coverage of deep seismic reflection data. We have developed a depth migration method suitable for processing deep seismic data. It includes the following procedures. The upwind finite‐difference method is used for calculation of traveltime. Velocity analysis with high resolution employs a combination of co‐variance analysis, joint inversion of RMS velocity and reflection two‐way times, and a Kirchhoff prestack depth migration scheme sequentially. After using these velocity analysis methods on semblance gathers, the finite‐difference reverse depth migration is applied for imaging the crust. This prestack depth migration scheme has been used to process 2D deep seismic reflection data obtained in Donghai County for site selection of Chinese Continental Scientific Drilling Program. The resultant migration produces a good‐resolution profile for imaging the crustal structures and a velocity model for locating lithology of the ultrahigh pressure metamorphic rocks.