Plate-Scale Strike-Slip Fault System in the Barbados Accretionary Wedge of the Lesser Antilles Subduction Zone

Abstract

Fault systems of various geometries develop into accretionary wedges to accommodate slip partitioning of plate convergence in oblique settings. However, how they form, evolve and contribute to the segmentation of the megathrust is still poorly understood. The Barbados accretionary wedge, which results from the subduction of the American plates beneath the Caribbean Plate at 2 cm/yr in a southwesterly direction, is one of the largest on Earth. Here we present a comprehensive morphotectonic study of this wedge based on a new marine geophysical data set acquired during the recent CASEIS marine experiment combined with legacy data sets. From a joint analysis of high-resolution bathymetry and seismic reflection profiles, we characterize a regional-scale left-lateral strike-slip fault system in the wedge, which began to form in Pliocene times and is still active today. It may relay, via a diffuse complex deformation system, to the Bunce left-lateral strike-slip fault in the north and may join the conjugate Kitridge right-lateral fault to the south. Both Bunce and Kitridge faults are themselves linked via relay zones to the main strike-slip fault systems bounding the Caribbean plate. They likely developed along the toe of the backstop and may mark a segmentation of the Lesser Antilles megathrust. The main segment of this system is the newly identified ∼580-km-long Seraphine fault, which is long enough to rupture during magnitude class 8 earthquakes. The kinematics of the entire fault system is incompatible with present-day NE-SW compression inferred at the Caribbean/American plate boundary and raises questions about the current geodynamics of the region.