Earthquakes track subduction fluids from slab source to mantle wedge sink

Abstract

Subducting plates release fluids as they plunge into Earth’s mantle and occasionally rupture to produce intraslab earthquakes. It is debated whether fluids and earthquakes are directly related. By combining seismic observations and geodynamic models from western Greece, and comparing across other subduction zones, we find that earthquakes effectively track the flow of fluids from their slab source at >80 km depth to their sink at shallow (<40 km) depth. Between source and sink, the fluids flow updip under a sealed plate interface, facilitating intraslab earthquakes. In some locations, the seal breaks and fluids escape through vents into the mantle wedge, thereby reducing the fluid supply and seismicity updip in the slab. The vents themselves may represent nucleation sites for larger damaging earthquakes.

Coupled Evolution of Deformation, Pore Fluid Pressure, and Fluid Flow in Shallow Subduction Forearcs

“…Numerous studies of fault friction suggest that (1) enhanced consolidation (and hence higher rigidity) favors the buildup of elastic strain energy in the wall rocks and (2) an increase in fault‐normal stress should promote frictional instability (e.g., Scholz, 1998; Marone & Saffer, 2007; Leeman et al, 2016). This is consistent with observations at some margins indicating megathrust downstepping, and that earthquake or tremor behavior changes abruptly where it is intersected by upper plate splay faults (Bangs et al, 2004; Bécel et al, 2017; Halpaap et al, 2019; Ranero et al, 2008; Wallace et al, 2009; Wells et al, 2017). This localized fault‐drainage effect appears to be more pronounced when the sediment‐matrix k is higher (e.g., model MK2); this is expected because the extent of drainage around the fault conduits should be primarily limited by the ability of fluids to access the faults via intergranular flow in the sediment matrix (Saffer, 2015).…”

“…Deformation and faulting, in turn, influence fault and sediment permeability—and therefore affect drainage and pore pressure—as well as the evolution of stress and mechanical loading. For example, interconnected fractures near fault zones form effective pathways that accommodate volatile fluxes and focus fluid seepage (drainage), enhancing the rates of consolidation and dewatering at depth (e.g., Lauer & Saffer, 2012, 2015) and potentially affecting megathrust slip behavior within the seismogenic and tremor zones (Halpaap et al, 2019; Ranero et al, 2008; Wells et al, 2017). In this study, we systematically investigate these processes and their fundamental feedbacks, using a numerical approach that fully couples mechanical loading, deformation, and fluid drainage.…”

Seismic Evidence for Water Transportation in the Forearc off Northern Japan

“…One explanation is that the slab dehydration has started to occur at a depth of <50 km. Another possibility is that a considerable amount of water, released from dehydration of the subducted oceanic crust in the deep part, migrates upward to the shallow part of the slab (Halpaap et al, ; Shiina et al, ). Therefore, we propose that the inferred dry forearc mantle is more affected by the possible low permeability of the slab interface (Halpaap et al, ; Katayama et al, ) than the possible low slab hydration.…”

“…Another possibility is that a considerable amount of water, released from dehydration of the subducted oceanic crust in the deep part, migrates upward to the shallow part of the slab (Halpaap et al, ; Shiina et al, ). Therefore, we propose that the inferred dry forearc mantle is more affected by the possible low permeability of the slab interface (Halpaap et al, ; Katayama et al, ) than the possible low slab hydration. In future tomographic studies, detailed images of S wave velocity and Poisson's ratio should be determined to clarify the fine structure and properties of the subducted oceanic crust in the study region.…”

“…The seismicity in the forearc mantle wedge (Figure ) may be triggered by fluids escaping through vents on the sealed slab interface (Halpaap et al, ; Nakajima & Uchida, ), which may also lead to the generation of slow‐slip events (Audet & Bürgmann, ). This interpretation is consistent with our result that large megathrust earthquakes ( M w ≥ 6.0) are mainly located near the low‐V anomalies at the slab interface (Figures e, , S7i, and S7l), which may reflect fluids released from the slab dehydration (Liu et al, ).…”