Ongoing tectonic subsidence in the Lesser Antilles subduction zone

Abstract

Geological estimates of vertical motions in the central part of the Lesser Antilles show subsidence on timescales ranging from 125.000 to 100 yr, which has been interpreted to be caused by interseismic locking along the subduction megathrust. However, horizontal GNSS velocities show that the Lesser Antilles subduction interface is currently building up little to no elastic strain. Here, we present new present-day vertical velocities for the Lesser Antilles islands and explore the link between short- and long-term vertical motions and their underlying processes. We find a geodetic subsidence of the Lesser Antilles island arc at 1-2 mm yr-1, consistent with the ∼100-yr trend derived from coral micro-atolls. Using elastic dislocation models, we show that a locked or partially locked subduction interface would produce uplift of the island arc, opposite to the observations, hence supporting a poorly coupled subduction. We propose that this long-term, margin-wide subsidence is controlled by slab dynamic processes, such as slab rollback. Such processes could also be responsible for the aseismic character of the subduction megathrust.