GNGTS 2024 - Atti del 42° Convegno Nazionale

Session 1.3 GNGTS 2024 Exploring Mantle Dynamics of the Cascadia Subducton System through Anisotropic Tomography with Transdimensional Inference Methods Brandon P. VanderBeek 1 , Gianmarco Del Piccolo 1 , Manuele Faccenda 1 1 Dipartmento di Geoscienze, Università degli Studi di Padova, Padova, Italia The Cascadia subducton system is an ideal locaton to investgate the nature of mantle fow and associated driving forces at a convergent margin owing to the dense network of on- and of-shore seismic instrumentaton. While numerous shear wave splitng and tomography studies have been performed with these data, they have produced confictng views of mantle dynamics collectvely referred to as the Cascadia Paradox. On the overriding plate, splitng observatons are consistent with large-scale 3D toroidal fow while of-shore splitng paterns are more easily explained by 2D plate-driven fow. Either geometry is difcult to reconcile with seismic tomographic models that image a fragmented Juan de Fuca slab descending beneath the Western USA. However, these observatons ofer only an incomplete image of Cascadia mantle structure. Shear wave splitng provides a depth integrated view of anisotropic fabrics making inferences regarding the 3D nature of mantle deformaton difcult. Prior high-resoluton body wave tomography typically neglects anisotropic efects which can in turn yield signifcant isotropic imaging artefacts that complicate model interpretaton. To overcome these limitatons, we invert P-wave delay tmes for a 3D hexagonally anisotropic model with arbitrarily oriented symmetry axes using the reversible jump Markov chain Monte Carlo algorithm. This stochastc imaging approach is partcularly well-suited to the highly non-linear and under-determined nature of the anisotropic seismic tomography problem. The resultng ensemble of solutons allows us to rigorously assess model parameter uncertaintes and trade-of between isotropic and anisotropic heterogeneity. We investgate whether the fragmented nature of the subducted Juan de Fuca slab is a well-resolved feature and to what extent its geometry trades of with anisotropic parameters. In light of our new 3D anisotropic model, we re-evaluate the Cascadia Paradox and atempt to reconcile disparate views of Western USA mantle dynamics. Corresponding author: brandonpaul.vanderbeek@unipd.it