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

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) m(2) to 10(-13) m(2), 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 decollement 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. Citation: Lauer, R. M., and D. M. Saffer (2012), Fluid budgets of subduction zone forearcs: The contribution of splay faults, Geophys. Res. Lett., 39, L13604, doi:10.1029/2012GL052182.