Dehydration-induced instabilities at intermediate depths in subduction zones

Nicolas Brantut (1) , Ioannis Stefanou (2) , Jean Sulem (2)

1 UCL - University College of London [London]
2 navier umr 8205 - Laboratoire Navier

We formulate a model for coupled deformation and dehydration of antigorite, based on a porosity-dependent yield criterion and including shear enhanced compaction. A pore pressure and compaction instability can develop when the net volume change associated with the reaction is negative, i.e., at intermediate-depth in subduction zones. The instability criterion is derived in terms of the dependence of the yield criterion on porosity: if that dependence is strong, instabilities are more likely to occur. We also find that the instability is associated with strain localisation, over characteristic length scales determined by the hydraulic diffusivity, the elasto-plastic parameters of the rock, and the reaction rate. Typical lower bounds for the localisation length are of the order of 10 to 100 m for antigorite dehydration and deformation at 3 GPa. The fluid pressure and deformation instability is expected to induce stress build-up in the surrounding rocks forming the subducted slab, which provides a mechanism for the nucleation and propagation of intermediate-depth earthquakes.

Domaines: Sciences de la Terre; Mécanique [physics]

Nicolas Brantut, Ioannis Stefanou, Jean Sulem. Dehydration-induced instabilities at intermediate depths in subduction zones. Journal of Geophysical Research : Solid Earth, 2017, ⟨10.1002/2017JB014357⟩. ⟨hal-01568176⟩