Vertical tectonic motions in the Lesser Antilles: linking short- and long-term observations

Horizontal GPS velocities show that the Lesser Antilles subduction zone is currently experiencing low interseismic coupling, meaning that little to no elastic strain is building up as the North- and South American plates subduct beneath the Caribbean plate. However, geological data on Quaternary coral terraces and active micro-atolls in the central part of the arc reveal slow subsidence over the past 125,000 to 100 years, likely tectonic in origin. It has been proposed that coupling along the subduction interface could be responsible for this geological subsidence. We use forward elastic models with a realistic slab geometry to show that a locked subduction interface would actually produce uplift of the island arc, which contradicts these geological observations. We also show that vertical GPS data in the Lesser Antilles indicates a subsidence of 1-2 mm/yr of the entire arc. This short-term subsidence is in agreement with the ~100-year trend of 1.1 mm/yr subsidence derived from coral micro-atolls in eastern Martinique. Since locking of the subduction interface is inconsistent with this observed subsidence of the arc, we explore other mechanisms that could this observation, such as postseismic effects of historical earthquakes, slab retreat, tectonic erosion, accretionary wedge collapse or extension in the overriding plate.