Elastic imaging with OBS receiver-side multiples

Receiver-side water-column multiples acquired with ocean-bottom seismic sensors can be used for elastic imaging of the subsurface, which can provide additional information relative to more conventional acoustic imaging. These multiples can be separated from primaries contained in ocean-bottom seismic data using techniques such as up/down decomposition. In elastic imaging, the down-going wavefield consists of only P-waves because multiples propagate through the water-column. Receiver-side water-column multiples can be imaged by backpropagation from virtual receivers located at symmetric positions relative to the ocean surface, thereby increasing the imaging aperture. We perform imaging in the angle domain, which enables us to reverse the reflection polarity change at normal incidence. In addition to physical reflections, a strong solid/liquid interface at the ocean bottom generates unwanted mode conversions which are present in the images in the form of cross-talk between physical and non-physical events. However, this cross-talk can be easily identified in shot-domain or image-domain commonimage gathers, and can therefore be removed after imaging. In the end, our procedure leads to a collection of images accounting for different combinations of incident and reflected P and S waves. These images exploit surface-related multiples, and are therefore the expression of different subsurface illumination relative to the analogous reflections using primary reflections only. Such elastic images can be used to infer accurate lithological information about the subsurface using angle-dependent reflectivity for different combinations of incident and reflected waves.