How to Detect Water in the Mantle Wedge of a Subduction Zone Using Seismic Anisotropy

E. Kaminski (1) , D. A. Okaya

1 IPGP - Institut de Physique du Globe de Paris

In approximately one fourth of worldwide subduction zones, seismic observations indicate a rotation from trench-normal to trench-parallel fast axis orientations in the mantle wedge. To interpret this observation we predict the evolution of crystal lattice preferred orientation in mantle wedge material as a function of the amount of water by using a model of polycrystal deformation (D-Rex) coupled with an analytical corner flow. The resulting seismic signature is obtained from synthetic seismic wave propagation through this mantle wedge. We identify that progressive hydration produces the rotation of fast axis orientations and can generate between the two zones of trench-parallel and trench-normal fast axis orientations a morph zone with very small anisotropy and a related decrease in P and S wave velocities. Such a morph zone is not produced by trench-parallel flow, hence this signature can be used to detect water in the mantle wedge.

Keywords: Subduction zones; Seismic anisotropy; Trench parallel flow; Water induced anisotropy; Lau Basin

Domains: Sciences of the Universe [physics]

E. Kaminski, D. A. Okaya. How to Detect Water in the Mantle Wedge of a Subduction Zone Using Seismic Anisotropy. Geophysical Research Letters, 2018, 45, pp.13,298-13,305. ⟨10.1029/2018GL079571⟩. ⟨insu-03589304⟩