As we approached Ocho Rios, Jamaica and the end of our expedition, the science team got together and summarized our new and exciting findings. We mapped the northern boundary of the Caribbean plate between Haiti and Jamaica across the Jamaica Passage. Here the submerged portion of the plate boundary is the Enriquillo-Plantain-Garden Fault. The fault is manifested by a deep trough. This trough contains three 2.5- to 3-kilometer-deep basins — the Motley, Navassa, and Moran basins — which were the focus of our study. We collected 50 seismic sub-bottom profiles and 47 sediment cores in the basins.
The Enriquillo-Plantain-Garden Fault is clearly “transpressional,” meaning it accommodates lateral and compressional motions. Evidence of compressional motions are generally manifested as folded sediment layers that increase in frequency and amplitude from south to north. This compression is shifting a 50-meter-high ridge from north to south. This ridge is the surface expression of the fault and suggests that interaction between compression and shortening along the fault is shifting the plate boundary to the south.
We anticipate that large earthquakes along the Enriquillo-Plantain-Garden Fault remobilized sediment and formed event deposits. The very different sediment types composed of calcareous microfossils and iron-rich mineral grains will help to identify the deposits and their sources — microfossils raining from the water column and minerals derived from exposed basalt outcrops. The ages of the event deposits will yield a record of historic and pre-historic earthquakes along the plate boundary and help to understand the geohazards for the populations that inhabit Jamaica and Haiti.