| Abstract: | Deformation along the margin of the Caribbean Plate is the principal cause of the tsunami threat in the Caribbean. That margin parallels the northern coast of South America, the Lesser Antilles, and extends along the Greater Antilles from Puerto Rico through Jamaica. The eastern boundary of the Caribbean plate near the Lesser Antilles is the locus of subduction of Atlantic seafloor. At least three distinct, shallow tectonic regimes parallel the margin. They are: an outer tectonic belt where the North America Plate bends to enter the subduction zone, the main interface or zone of contact between the plates, and an inner zone of intraplate activity in the overriding Caribbean Plate. The level of seismic activity and tsunami potential in each of these zones is influenced by the presence of aseismic ridges on the downgoing plate. Ridges may increase the probability of tsunami or slow earthquakes, by reactivating thrust faults in the accretionary prism. The northeastern corner of the Caribbean Plate margin has a smooth transition from the relatively simple subduction zone in the Northern Lesser Antilles into a region of oblique convergence. It is a complex margin dominated by microplate tectonics from near Puerto Rico through Hispaniola. Here too the same three tectonic zones can be defined, but the third zone, “intraplate activity in the Caribbean Plate”, is more clearly delineated as microplate deformation in a wide plate boundary zone. Strike-slip tectonics dominates the region from Haiti westward to the northern coast of Honduras. Local bends in the transcurrent fault systems lead to vertical tectonics in the form of push-ups and pull-aparts. Some convergence is absorbed along the southernmost margin of Cuba. Either the tsunamigenic events in this region had source mechanisms with significant vertical components, or they triggered submarine landslides that generated the tsunami. Other potential sources lie along the northern coast of South America ands off the east coast of Central America. Manipulation of gridded bathymetric data to produce maps of seafloor slope, slope direction, and roughness as defined by the curvature of contours, can aid the identification of potential slides/slumps, or reveal portions of subduction zones more likely to produce tsunami earthquakes. A survey of the Caribbean Basin reveals several regions of high slope. Many of these are found where great earthquakes have or are likely to occur, possibly triggering submarine landslides. Regions such as the southern Lesser Antilles have steeper seafloor slopes in the backarc region than in the accretionary prism of the subduction zone. It has been suggested that subduction of rough seafloor highs such as seamounts and fracture zones leads to dewatering and stiffening of the accretionary prism and, as the high enters the deeper portions of the subduction zone, activation of thrust faults within the accretionary prism i.e. above the main decollement. If this were the case, it would enhance the possibility of tsunami or slow earthquakes. The subduction of rough bathymetric highs and its corresponding increasing roughness of the accretionary prism would then be another parameter to determine the likelihood of tsunami earthquakes. Using these criteria, several regions of the NE Caribbean stand out as more likely source for tsunami earthquakes. |
