THE CARIBBEAN PLATE: A NATURAL LABORATORY FOR THE STUDY OF THE STRUCTURE AND SEISMIC POTENTIAL OF ACTIVE STRIKE-SLIP FAULTS

Although the Caribbean is a relatively small plate, over 5100 km of its plate edges are bounded by strike-slip faults ranging from single continental-style plate boundaries to broader zones of transpressional or transtensional strain partitioning. Steadily-improving GPS data from the Caribbean margins allow for quantitative comparisons between the structure of individual fault zones and the observed style of strike-slip deformation using a variety of onland and submarine mapping methods. Single continental-style plate boundaries like those separating the Caribbean plate from the neighboring North and South American plates exhibit discrete segments ranging in length from 200 to 1000 km that transition with changing plate motion from transtension, to pure strike-slip, to transpression. Transtension in the offshore Honduras area (defined by obliquity of plate motion in range of 5-20°) produces continental borderlands provinces that resemble zones of pure rifting on seismic profiles. Transpression in the range of 5-15° produces elongate, mini-fold-thrust belts in a submarine setting (southern Cuba). Oblique collision in the range of 15-30° as observed on the 3-km-high island of Hispaniola produce a 250-km-wide outer zone of subduction and inner zone of partitioned strike-slip faults. Pure strike-slip deformation produces the simplest pattern of deformation in the form of remarkably narrow and continuous zones of linear strike-slip faults (Cayman trough, El Pilar system). Active strike-slip faults are closely guided along the suture formed by collision of the Caribbean arc against thicker continental crust as well seen by abrupt steps in the Moho between thinner arc and thicker continental crust along the South American margin. The most divergent arrays of strike-slip faults across the widest areas are associated with collisional indentation as observed in northwestern South America as a result of the Panama arc collision. Older strike-slip faults become cryptic when they are overprinted by a younger phase of compression (northwestern South America) or extension (northern Central America). Perhaps the most puzzling active strike-slip faults are those driven as intact but narrow narrow slivers by varying amounts of oblique subduction (Cocos-Caribbean arc, Puerto Rico trench). A common trait shared by all Caribbean strike-slip faults and tragically seen by the 2010 Haiti earthquake is their relatively slow slip rates (7-12 mm/yr range) that allows for strain accumulation over centuries. The seismic cycle of relatively benign strain accumulation is terminated by shallow and destructive M6-7 earthquakes unleashed on unsuspecting populations not accustomed to or prepared for these infrequent events.