Ongoing tectonic subsidence in the Lesser Antilles subduction zone

Abstract

It has been proposed that interseismic coupling along the Lesser Antilles subduction interface could be responsible for subsidence observed over the past 125,000 to 100 years inferred from geological data on Quaternary coral terraces and active micro-atolls in the central part of the arc. However, horizontal GNSS velocities show that the Lesser Antilles subduction zone is currently experiencing low interseismic coupling, meaning that little to no elastic strain currently builds up as the North-and South American plates subduct beneath the Caribbean plate. Here we show, using modern geodetic data, a general subsidence of the Lesser Antilles island arc at 1-2 mm/yr over the past 20 years, in agreement with the ~100-year trend of 1.3 ± 1.1 mm/yr subsidence derived from coral micro-atolls in eastern Martinique. Using elastic dislocation models, we show that a locked, or partially locked subduction interface would produce uplift of the island arc, opposite to present-day and recent geological observations, hence supporting a poorly-coupled subduction. This subsidence since at least 125 ka is in line with the extensional tectonics observed along the arc since the mid-Miocene. The margin-wide subsidence is therefore likely controlled by large-scale geodynamic processes that operate over the long-term. Such processes could also play a role in tuning the aseismic character of the subduction megathrust, which appears to be a long-term feature.