Subduction zone

The region containing a descending plate, its interface and the associated upper-plate and mantle wedge system.

A coupled phenomenon in which transient slow fault slip occurs with low-frequency seismic tremor, often near the downdip transition from locked to steadily creeping parts of a megathrust. Geodetic displacement and seismic signals provide complementary observations. Along-strike differences in recurrence, migration and cumulative slip help characterize subduction zone segmentation; tremor counts alone do not uniquely give fault slip or coupling.

Along-strike changes in the structure, deformation, coupling or thermal state of a subduction zone. Segments inferred from megathrust locking, episodic tremor and slip, past earthquake ruptures, slab dip and seismic tomography need not have identical boundaries. A common spatial pattern can motivate a physical hypothesis, but does not alone prove a persistent rupture barrier or identify a unique cause.

The subduction zone beneath the Pacific Northwest of North America, where the Juan de Fuca Plate and adjacent oceanic plates descend beneath the North American Plate.

An accreted basaltic terrane forming important parts of the forearc basement in the Pacific Northwest. Spatial variations in its thickness, stiffness and permeability can affect the interpretation of gravity anomalies and the fluid/stress environment above the megathrust. A proposed relation to central Cascadia creep uses gravity, geodetic and paleoseismic observations, rather than lithology alone.^[ref]

The wedge-shaped mantle above a descending slab, whose circulation and chemical modification influence arc magmas.

The upper-plate region between the subduction trench and volcanic arc.

A wedge of material transferred from the incoming plate to the overriding plate by offscraping or underplating.

The mantle of the overriding plate beneath the forearc, potentially hydrated by slab-derived fluids.

A sedimentary basin within the forearc.