1 Introduction
Earthquake rupture forecasts rely in part on geologic deformation models
that combine fault geometries and long-term fault slip rates (Field et
al., 2014; Hatem et al., 2022). For subduction interfaces, deformation
models can be difficult to construct because simple notions of fault
slip rates do not apply to subduction systems. This is because geodetic
coupling varies along strike and downdip (Chlieh et al., 2008;
Freymueller & Beavan, 1999; Lay et al., 2012; Pacheco et al., 1993;
Scholz & Campos, 2012; Wang, 1995) and strain release along subduction
interfaces can be complicated by complex, overlapping patterns of
aseismic, coseismic, and postseismic slip and upper-plate structures
such as splay faults (Barnhart et al., 2016; Liberty et al., 2013).
Because aseismic slip is nearly ubiquitous in the subduction setting,
fault slip rates are replaced by the concept of slip deficit rates,
which represent the long-term plate convergence rate times the coupling
coefficient along the subduction interface determined geodetically
(Pacheco et al., 1993). The coupling coefficent ranges from 0 (or 0%)
when the interface is fully decoupled and the interseismic (aseismic)
slip rate is equal to the local plate convergence rate, to 1 (or 100%)
when the interface is fully locked and the slip deficit rate equals the
local plate convergence rate (Pacheco et al., 1993).
Recurrence estimates based on paleoseismic data are especially important
in subduction zones because the return times of the largest subduction
earthquakes greatly exceed the length of historical seismic catalogs and
slip deficit rates are not easily converted to earthquake rates (Nelson
et al., 2021; Satake & Atwater, 2007). Subduction paleoseismology
provides estimates of earthquake recurrence from abrupt changes in
relative sea level recorded by geologic archives, such as coastal marsh
stratigraphy (Atwater, 1987) and coral microatolls (Taylor et al.,
1987). Indirect proxies for subduction interface rupture include
turbidites (Adams, 1990; Goldfinger et al., 2012) and tsunami inundation
(Witter et al., 2016).