Coulomb stress evolution in NE Caribbean over the past 250 years due to coseismic, postseismic and interseismic deformation

The northeastern Caribbean region marks the active boundary between the North American and Caribbean plates, accommodating ~20 mm/yr of oblique relative plate convergence distributed between the subduction interface and major strike-slip faults within the overriding plate. This heavily populated region has experienced eleven large (M≥7.0) earthquakes over the past 250 years. In an effort to improve our understanding of the location and timing of these earthquakes and to understand where current seismic hazards may be greatest, we calculate the evolution of Coulomb stress in the region since 1751 due to coseismic slip from all known large earthquakes, associated postseismic viscoelastic relaxation of a mobile mantle, and long-term interseismic deformation. The deformation field is calculated using spheroidal and toroidal modes of a spherically stratified viscoelastic earth, with interseismic deformation constrained by a block model based on geodetic, geologic and seismic observations. We find that the observed progressive westward propagation of earthquakes on major fault systems (i.e., the Septentrional and Enriquillo strike-slip faults and the megathrust) was encouraged by coseismic stress changes associated with prior earthquakes. For the strike-slip faults, the loading of adjacent segments was further amplified by postseismic relaxation of a viscoelastic mantle in the decades following each event. Furthermore, earthquakes on the Septentrional fault relieve a small level of Coulomb stress on the parallel Enriquillo fault to the south (and vice-versa), perhaps explaining the anti-correlated timing of events on these respective fault systems. The greatest net build-up of Coulomb stress changes over the past 250 years occurs along the central and eastern segment of the Septentrional and the Bowin strike-slip faults, as no recent earthquake has relieved stress in these regions. For oblique thrust faults, net stress build-up over the past 250 years is largest on the North American/Caribbean megathrust west of 70.5°W. High Coulomb stress has also developed east of 65.5°W, where no historic events have been inferred to have relieved stress, though limited GPS coverage in this region may have led to over-estimation of interseismic slip deficit rates in this area.