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10 st / September 2017 www.sea-technology.com ally demanding processes are now becoming economically feasible, even if currently reserved for the most challenging of sites. This ready availability of computing resources has also coincided with recent growing interest in applying similar inversion techniques to the foundation and top-hole drilling zones (tens of meters to circa 1.5 km below the seabed). Al- though being used by some, the inversion of site-survey data is a long way from being a standard tool. Typically, within the site-survey community, there remain fundamental un- answered questions surrounding: What exactly is seismic inversion; how does one go about using/applying it; where is it most effectively employed in a site survey or ground- modeling workflow; what can realistically be achieved for geotechnical engineering applications today; and what might be possible to achieve in the near future (i.e., over the next five years)? In this article, we attempt to address some of these questions and propose some, but far from all, of the answers. Finally, we outline some of what we consider to T he inversion of seismic reflection data to derive quan- titative information about the subsurface has become a much-valued and regularly used tool for reservoir char- acterization. The term "inversion" is used because the fun- damental objective is to derive the subsurface conditions that created the observed seismic reflection response (i.e., reverse or "invert" the seismic reflections). There are a vari- ety of inversion methods, but the majority can be grouped under the umbrella term "seismic inversion." Seismic inver- sion covers everything from the computationally fast, but limited, post-stack acoustic impedance inversion to the ex- tremely computationally demanding, but highly detailed, anisotropic elastic full-waveform inversion. With the emergence of easily accessible high-perfor- mance computing, the less computationally demanding in- version processes are today considered standard, run-of-the- mill tools, with most reservoir interpretation now carried out on inverted impedance data, rather than the recorded seis- mic reflection amplitude data. Even the most computation- An Emerging Tool In the Site Investigation Toolbox Seismic Inversion Reduces Uncertainties in Site Characterization By Dr. Mark E. Vardy • Andrew W. Hill • Kerry J. Campbell Flow chart illustrating the seismic inversion process. Orange boxes represent inputs and outputs of the workflow, while blue boxes are key stages within the looped workflow.