Reverse Time Migration Using Excitation Amplitude Imaging Condition Based on Accurate First-Arrival Traveltimes Calculation

Reverse time migration (RTM) can provide high-quality seismic images and is one of the most advanced migration methods. Imaging condition method is a crucial component in RTM. Different imaging conditions show different abilities to obtain image amplitude, physical validity, and resolution. The cross-correlation imaging condition can achieve high imaging accuracy for complex structures. Nevertheless, this approach necessitates the storage of almost the entire source wavefields, which demands a substantial amount of storage space and consequently reduces the computational efficiency of reverse time migration. In contrast, the excitation amplitude imaging condition, which relies solely on wavefield information at the imaging time, eliminates the necessity for extensive storage, thereby enhancing the computational efficiency of reverse time migration. However, conventional methods determine the imaging time by identifying the maximum amplitude of the source wavefield at each grid point. In scenarios involving large offsets or strong reflection interfaces, this approach can lead to inaccuracies in determining the imaging time. In this paper, we utilize an advanced adaptive finite-difference operator method to solve the eikonal equation for determining imaging time. This approach markedly enhances the accuracy of first-arrival traveltimes calculations at near offsets, which is especially critical for seismic imaging. Numerical examples from simple model, the Marmousi model, and field seismic data demonstrate the effectiveness of our proposed method.