Table 1.

Basic definitions of common terms used herein

phenomenon	definition and notes
slow slip and tremor (SST)	General term used here for plate boundary slip transients that are commonly associated with observable surface deformation over days to years and that are illuminated by low intensity seismic emissions known as tectonic tremor
slow slip events (SSEs)	Aseismic fault slip transient with durations ranging from minutes to decades. Also referred to as slow earthquakes, silent earthquakes and creep events.
episodic tremor and slip (ETS)	SSEs with abundant tremor, typically months or less in duration, found at and around the mantle wedge corner of some subduction zones. More narrowly defined type of periodic slow slip transients with tremor based on the characteristics found in southwest Japan and Cascadia-type localities.
low frequency earthquakes (LFE)	Small and short low frequency (2–8 Hz) seismic events contained in tectonic tremor signal indicative of fault slip. See table 2 for details.
very low-frequency Earthquakes	Similar to LFEs but lower frequency (less than 0.1 Hz), longer duration (10–200 s) and larger (M 3–4).
subduction interface	The region between the subducting slab and the overriding plate in subduction zones that accommodates differential motion between the two plates. It can be a fault, an anastomosing fault zone or a finite-width shear zone.
tectonic underplating	The progressive transfer of material from the top of the subducting slab to the upper plate, and the associated down-stepping of the subduction interface into deeper levels of the downgoing plate. Underplated material may derive originally from the downgoing slab, but can also be eroded updip from original or previously accreted material in the overriding plate.
asperity	Defined here as a feature on a fault that exhibits different rheological properties from surrounding regions. Often used to describe areas that will eventually fail by seismic rupture.
melange belt	A general term used here to refer to a fault- or shear- zone with rock types that exhibit strong competency contrasts such that a ‘block-in-matrix’ texture is visible at the outcrop or larger scale. Does not necessarily require the presence of exotic blocks or large-scale mechanical mixing.
pressure solution creep	A deformation mechanism common in rocks in subduction (and other fluid-rich) environments. It involves dissolution of minerals along grain boundaries in areas of relatively high differential stress, accompanied by mass transfer within the fluid phase and eventual deposition of minerals in regions of relatively low differential stress. Produces strong foliations at high strains, known as pressure solution cleavages or cleavage microlithon fabrics. Also referred to as dissolution-precipitation creep or volatile-assisted diffusion creep.