Summary A 2‐D full wavefield inversion method is presented for the processing of wide‐aperture data. The diversity of information contained within such datasets may be handled in a complete manner by first matching the traveltimes of the main events and then progressing to waveform fitting of the data through explicit full wavefield modelling. Our wavefield inversion scheme is based upon a finite difference solution of the 2‐D elastic wave equation in the time distance domain. The strength of adopting such an approach is the ability to generate all possible wave types within a given 2‐D model (multiples, converted waves, etc.) and thus to simulate and accurately model complex seismic wavefields. The aim of the inversion is to find the 2‐D P‐wave velocity model that minimizes the least squared difference between the observed and synthetic data across the full range of offsets. Following extensive testing on synthetic data, the wavefield inversion scheme has been applied to wide‐aperture real marine seismic streamer datasets. We present results from the synthetic testing and the wavefield inversion of wide‐aperture real data out to 12 km offset that was recorded on a single streamer. Even though current computational restrictions allow only a small subsection of the data to be analysed, these examples demonstrate the potential value of wide‐aperture 2‐D full wavefield inversion.

A crosshole experiment was carried out in a layered sedimentary environment in which a normal fault is known to cut through the section. Initial traveltime inversions produced stable but low-resolution images from which the fault could be only vaguely inferred. To image the fault, wavefield inversion was used to produce a velocity model consistent with the detailed phase and amplitude of the data at a number of frequencies. Our wavefield inversion scheme uses a classical, descent-type algorithm for decreasing the data misfit by iteratively computing the gradient of this misfit by repeated forward and backward propagations. Our propagator is a full-wave equation, frequency-domain, acoustic, finite-difference method. The use of the frequencyspace domain yields computational advantages for multisource data and allows an easy incorporation of viscous effects.By running wavefield inversion on the field data, a quantitative velocity image was produced that yielded

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