The role of elasticity in slab bending

Loic Fourel (1) , Saskia Goes , Gabriele Morra

1 IPGP - Institut de Physique du Globe de Paris

Previous studies showed that plate rheology exerts a dominant control on the shape and velocity of subducting plates. Here, we perform a systematic investigation of the role of elasticity in slab bending, using fully dynamic 2-D models where an elastic, viscoelastic, or viscoelastoplastic plate subducts freely into a purely viscous mantle. We derive a scaling relationship between the bending radius of viscoelastic slabs and the Deborah number, De, which is the ratio of Maxwell time over deformation time. We show that De controls the ratio of elastically stored energy over viscously dissipated energy and find that at De>10-2, substantially less energy is required to bend a viscoelastic slab to the same shape as a purely viscous slab with the same intrinsic viscosity. Elastically stored energy at higher De favors retreating modes of subduction via unbending, while trench advance only occurs for some cases with De<10-2. We estimate the apparent Deborah numbers of natural subduction zones and find values ranging from 10-3 to > 1, where most zones have low De<10-2, but a few young plates have De > 0.1. Slabs with De<10-2 either have very low viscosities or they may be yielding, in which case our De estimates may be underestimated by up to an order of magnitude, potentially pointing towards a significant role of elasticity in ∼60% of the subduction zones. In support of such a role of elasticity in subduction, we find that increasing De correlates with increasing proportion of larger seismic events in both instrumental and historic catalogues.

Mots clés: elasticity; subduction; Deborah number; energy dissipation; b-values

Domaines: Planète et Univers [physics]

Loic Fourel, Saskia Goes, Gabriele Morra. The role of elasticity in slab bending. Geochemistry, Geophysics, Geosystems, 2014, 15, pp.4507-4525. ⟨10.1002/2014GC005535⟩. ⟨insu-03581064⟩