In this report, the truncated Newton (TN) method and its application to anacoustic FWI is investigated. Larger problems are shown to be efﬁciently solvable when using TN FWI instead of full Newton FWI. It is also found that stricter forcing terms are required in anacoustic FWI to achieve results comparable to acoustic TN FWI, due mostly to cross-talk effects. This additional cost can partly mitigated by using effective preconditioning and a CG inner solver, or better mitigated using a BFGS inner solver. Even with these strategies, signiﬁcant cost is incurred to accurately recover Q. If only velocity is desired, it can be effectively recovered for a lower cost.
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