Abstract Intermediate‐depth intraslab earthquakes in the Philippine Sea Plate occur at depths of 100–200 km beneath the Ryukyu Arc and are widely interpreted as manifestations of slab dehydration; however, the spatial variability in continuity of the volcanic front and the asymmetric distribution of volcanic activity are poorly explained by existing models. We demonstrate that spatial variations in the intraslab stress field control anisotropy in the permeability of the subducted slab, influencing the up‐dip migration of fluids and therefore the distribution of arc volcanism. By inverting the stress tensors of 184 focal mechanism solutions ( M w > 3.3) of earthquakes between 1997 and 2007, we identified heterogeneous intraslab stress regimes and evaluated how their mechanical expression, particularly the orientation of the intermediate principal stress axis ( σ 2 ), influences the direction of fluid flow. Our results show that regions characterized by down‐dip extensional stress regimes, in which σ 2 is oriented approximately perpendicular to the slab dip, coincide with enhanced permeability and efficient dehydration pathways toward the mantle wedge. These results highlight the pivotal role of intraslab stress in shaping fluid migration pathways and arc magmatism in the Ryukyu subduction zone.
Otsubo et al. (Fri,) studied this question.