Seismic elastic RTM with vector-wavefield decomposition

摘要

The advanced seismic imaging technology is reverse-time migration (RTM), which generates Earth's structural image by cross-correlating the forward-propagated source wavefield and the back-propagated receiver wavefield. Both these wavefields conventionally are assumed to be acoustic waves. When applying this RTM technology to seismic elastic waves, which are the multi-component rather than the single-component data, the cross-correlation procedure will suffer from a crosstalk effect between different wave modes. Therefore, prior to RTM imaging, both the source and receiver wavefields need to be decomposed into the pure P-wave mode and the pure S-wave mode. This paper envisages the advanced features of a vector-wavefield decomposition method that presents either the P- or the S-wave mode as a vector wavefield. This vector-wavefield decomposition method is based on a group of decoupled wave equations. The two separated vector wavefields preserve the true amplitude and phase information. Then, the associated RTM imaging condition is an inner-product of these two vector wavefields, rather than the cross correlation that is applicable to two scalar wavefields. The conventional elastic RTM approach uses the Helmholtz decomposition method to derive P- and S-waves and then implements cross correlation to produce the image. In comparison to this conventional combination, this paper demonstrates that the elastic RTM method using a combination of the vector-wavefield decomposition and the inner-product imaging condition is capable of producing seismic images with correct amplitudes and phases of various reflection modes.