Imaging the Twin Fault System Along the Northern Boundary of the Caribbean Plate

The northern plate boundary of the Caribbean tectonic plate is a complex tectonic zone. After the collision of Cuba with the Bahamas Carbonate Platform in the Eocene, several strike-slip faults accommodated the eastward movement of the Caribbean plate with the initiation of the westward dipping subduction at the Lesser Antilles arc. From the Miocene onwards, a twin fault system developed at Hispaniola with two major sinistral transform fault zones bounding the intervening and debated Gonâve microplate: the Septentrional- Oriente Fault Zone (SOFZ) to the north and the Enriquillo-Plantain Garden Fault Zone (EPGFZ) to the south. At present, these faults are associated with significant geohazards to the region, and their offshore segments are still poorly understood. Given the geometry of the plate boundary system, one would expect that only the SOFZ branch would be active and linked by the mid-Cayman ultra-slow spreading center to the Swan Island FZ that bounds the Cayman Trough to the south, further west. Instead, both the SOFZ and EPGFZ are active and have similar displacement rates, accumulating a 17-19 mm/yr left-lateral motion between the Caribbean and North American Plates. Following up on earlier scientific cruises that notably explored the sedimentary basins in the area of the faults, a recent multi-disciplinary scientific cruise investigated both deep and shallow structures in the area. The Haiti-TWiST (TWIn faults Seismic Transects) campaign took place on the R/V “Pourquoi pas?” from 30 May to 21 July, offshore Haiti, Cuba, Jamaica, and Navassa Island. The cruise was organized in two legs, and more than 40 scientists from many nationalities participated, as well as eight Master-1 students in the framework of a floating University (see blog on UMR Geo-Ocean Website). This presentation will highlight some of the preliminary results and will focus mainly on the bathymetry data acquired with the Reson Seabat 7150 Multibeam echosounder.