Fluid budgets of subduction zone forearcs: The contribution of splay faults

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Geochemical and geophysical evidence indicate that splay faults cutting subduction zone forearcs are a key hydraulic connection between the plate boundary at depth and the seafloor. Existing modeling studies have generally not included these structures, and therefore a quantitative understanding of their role in overall fluid budgets, the distribution of fluid egress at the seafloor, and advection of heat and solutes has been lacking. Here, we use a two‐dimensional numerical model to address these questions at non‐accretionary subduction zones, using the well‐studied Costa Rican margin as an example. We find that for a range of splay fault permeabilities from 10−16 m2 to 10−13 m2, they capture between 6 and 35% of the total dewatering flux. Simulated flow rates of 0.1–17 cm/yr are highly consistent with those reported at seafloor seeps and along the décollement near the trench. Our results provide a quantitative link between permeability architecture, fluid budgets, and flow rates, and illustrate that these features play a fundamental role in forearc dewatering, and in efficiently channeling heat and solutes from depth.