Elastic Transmitted Wave Reverse Time Migration for Imaging Earth?s Interior Discontinuities: A Numerical Study

Seismic imaging is crucial in investigating Earth's interior structures and understanding its tectonics and evolution. The reflected, converted, and scattered waves have attracted considerable attention in the previous studies, whereas the directly transmitted waves are less used in seismic imaging. In this study, we present a novel passive source elastic transmitted wave reverse time migration (T-RTM) method to characterize major discontinuities in Earth's interior using transmitted P or S waveforms. By extrapolating and then cross correlating the wavefields from the sources with the transmitted wavefields from the receivers using flood velocity models, the velocity discontinuities can be clearly imaged. The advantages and potential applications of the proposed T-RTM method are demonstrated with three synthetic imaging experiments. First, with distributed acoustic sensing using submarine cables, we show that the proposed method can be used to image the Moho with teleseismic S waves recorded in a single axial component, which is difficult for other imaging methods. Second, using direct P waveforms with a single P-wave velocity model, we show that the proposed method can be used to image 3D Moho topography without relying on the VP= VS ratio like in the traditional receiver function imaging. Third, the proposed method can also be used to image a fault plane with a sharp velocity contrast using local earthquakes. We discuss the limitations of the proposed method and some potential issues in field-data applications with additional numerical experiments. The proposed TRTM method could provide many new opportunities for utilizing transmitted waveforms in the study of oceanic and continental structures.