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Article Dans Une Revue Seismica Année : 2022

Bayesian approach to the tomographic problem with constraints from geodynamic modeling: Application to a synthetic subduction zone

Résumé

Geodynamic tomography, an imaging technique that incorporates constraints from geodynamics and mineral physics to restrict the potential number of candidate seismic models down to a subset consistent with geodynamic predictions, is applied to a thermal subduction model. The goal is to test its ability to recover structures harboring complex deformation patterns. The subduction zone is parameterized in terms of four unknown parameters that define its thermal structure: slab length L, thickness R, temperature Tc, and dip angle θ. A temperature-dependent viscosity is prescribed with an activation coefficient E controlling the sensitivity. Using the full forward approach to geodynamic tomography, we generate anisotropic surface wave dispersion measurements as synthetic data. We retrieve the five unknown parameters by inverting the synthetics corrupted with random uncorrelated noise. The final output is an ensemble of models of L, R, θ, Tc, and E cast in a posterior probability distribution with their uncertainty limits. Results show that the parameters are tightly constrained with the apparent existence of a single misfit minima in each of them, implying the implicit retrieval of the complete patterns of upper mantle deformation, and the 21-independent coefficients defining elastic anisotropy. Each model realization, however, fails to swarm around its true value. Such results are attributed to the inability of the surrogate model to accurately replicate the correct forward model for computing anisotropy due to the complexity of the deformation patterns considered. Nevertheless, this proof of concept shows a self-consistent method that incorporates mantle flow modeling in a seismic inversion scheme. Non-technical summary Seismic tomography is an active area of research in seismology that primarily deals with the imaging of the Earth interior. Here, seismic data are used to recover the heterogeneous structure of the Earth at a given resolution in a process known as inversion. However, seismic inversion methods have to be constantly improved to accurately map these heterogeneities in order to correctly interpret them in terms of recent deformation mechanisms within the Earth. We introduce geodynamic tomography; a new imaging technique that infers the present-day temperature and mantle flow patterns from the inversion of surface wave measurements. We demonstrate this method in a subduction zone setting (an earthquake prone area where materials making up a tectonic plate are recycled into the mantle) by recovering some properties that define its thermal structure: length, thickness, angle of subduction, and slab core temperature.
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Dates et versions

hal-04313028 , version 1 (28-11-2023)

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John Keith Magali, Thomas Bodin. Bayesian approach to the tomographic problem with constraints from geodynamic modeling: Application to a synthetic subduction zone. Seismica, 2022, 1, ⟨10.26443/seismica.v1i1.201⟩. ⟨hal-04313028⟩
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