基于弹性反射波正演表达的转换波逆时偏移与反偏移

A primary reflected wave equation with the subsurfaces reflectivity function was proposed to solve the problem that conventional mathematical and physical formula can t simulate the linear elastic reflected wave propagation very well. Under the scattering wave propagation theory, the linear simulation method is used to refine the reflectivity function by approximating the spatial change of velocity perturbation with the high-frequency approximation. Then the primary reflected wave equation was extracted from scattering wave equation. Based on the linear expression of elastic reflection seismic data, reflection coefficient of the converted S wave can be approximately estimated by the adjoint of the linear operator and realize reflected converted wave reverse time migration. According to this linear expression, the paper realizes angle domain demigration and reconstructs the upward converted S wave. And then derives the gradient of image with respect to velocity by adjoint state method. Numerical test results show that the reverse time migration imaging based on elastic reflected seismic data could overcome polarity reversal and the imaging results contain reflected angle information. The primary reflected wave simulation method is precise and stable, and the reflected wave s amplitude and phase information are close to theoretical results, which effectively ensures the stability of solution of gradients of the migrated image with respect to velocity.