Towards High Resolution Localised Elastic Full Waveform Inversion

We present a methodology to invert seismic data for a localised area by combining source-side wavefield injection and receiver-side extrapolation method. Despite the high resolving power of seismic full waveform inversion (FWI), the computational cost for practical scale elastic FWI remains a heavy burden. This can be much more severe for time-lapse surveys, which require real-time seismic imaging on a daily or weekly basis. Besides, structure changes during time-lapse surveys are likely to occur in a small area rather than the whole region, such as oil reservoir. We thus propose an approach that allows to image effectively the localised structure changes far deep from both source and receiver arrays. We perform both forward and back propagation only inside the target region. We present 2D elastic numerical examples of the proposed method and quantitatively evaluate the inversion errors, in comparison to those of conventional full-model inversions. The results show that the proposed localised waveform inversion is not only efficient and robust but also accurate even under the existence of errors in baseline models. Besides, the proposed strategy has the potentiality in determining highresolution imaging of reservoir by inverting higher frequencies (above 30 Hz) at relatively low computational cost.