On the reliability of lithospheric constraints derived from models of outer‐rise flexure

SUMMARY We evaluate the common practice of utilizing elastic models of outer‐rise flexure to constrain lithospheric parameters, such as mechanical thickness and ambient in‐plane force. We numerically compute ‘synthetic’ flexural profiles consistent with empirically determined constraints on lithospheric rheology and representative trench‐type boundary conditions, and misfit minimization is utilized to determine the analytical solution to elastic‐plate flexure that most closely resembles each synthetic profile. We then determine if it is possible to use the best‐fitting elastic solutions to recover the lithospheric mechanical thickness and level of in‐plane force that were assumed during the numerical computation of the synthetic profiles. This methodology is analogous to the common practice of estimating lithospheric parameters by modelling bathymetric profiles with analytical descriptions of elastic‐plate flexure. Our results unequivocally indicate that in‐plane force cannot be reliably constrained in this manner. Such an approach does not even allow the qualitative nature of in‐plane force to be distinguished (i.e. compressional versus tensional). Although, in principle, elastic‐plate models may provide reliable constraints on the mechanical thickness of oceanic lithosphere, in practice uncertainties associated with bathymetric noise and the level of in‐plane force may, in some instances, render such constraints unreliable.