Predicting the geodetic signature of M W ≥ 8 slow slip events

Elastic dislocation models of geodetic measurements above subduction zones have led to the identification of M W ≈ 6.0–7.2 slow slip events (SSEs) that release elastic strain over periods of days to months, but great (M W ≥ 8) SSEs have remained unidentified. We extrapolate observations of SSE duration and slip magnitude to show that slip velocity decreases with event magnitude and predict that the slip velocity of M W ≥ 8 SSEs is ≤50 mm/yr. The slip velocity for great SSEs may never exceed the plate convergence rate and thus never produce a reversal in trench perpendicular motion. Instead, geodetically constrained estimates of apparent partial elastic coupling on subduction zone interfaces worldwide may be direct observations of ongoing M W ≥ 8 silent earthquakes with durations of decades to centuries.