SEISMICITY AND TECTONICS OF THE SOUTHEASTERN CARIBBEAN

We present 33 new focal mechanisms for SE Caribbean earthquakes (1963 1988). We use these mechanisms, in conjunction with 28 previously avai lable mechanisms, to distinguish between two models of plate boundary zone interaction in the SE Caribbean: the trench-trench transform and hinge faulting model, and the right oblique collision model. Shallow ( 0-70 km) and intermediate (70-200 km) depth earthquakes occur in the s tudy region; we focus on the tectonic causes of these events and the m otions they delineate. The shallow earthquakes are in a broad linear z one which trends NE from the Paria Peninsula of Venezuela towards Barb ados. Intermediate depth earthquakes cluster beneath and NW of the Pen insula, and deepen to the NW, perpendicular to the NE-trending shallow events. The vertical distribution of the earthquakes suggests a slab with steep NW dip. Shallow, dextral strike slip on E-striking faults i s restricted to a 60-km-wide linear zone between the Gulf of Cariaco a nd the western margin of the Gulf of Paria. Dextral strike slip is act ive only as far east as the Gulf of Paria, and not within or east of T rinidad. Shallow thrust events with ENE-striking planes, distributed b etween the Araya Peninsula and the Gulf of Paria, indicate collision a t crustal levels between South America and Caribbean, and that folding and thrusting are still active over a 60-km interval south of the Ara ya-Paria isthmus. Active thrusting in Venezuela corroborates predictio ns of transpression between Caribbean and South America and discounts transtensional motions between the two plates in the SE Caribbean. The conjunction of shallow thrust, strike slip, and normal earthquakes in the Gulf of Paria at around 62.3-degrees may be the expression of unp artitioned oblique compressive deformation in the plate boundary zone. Intermediate (165 km > h > 70 km) depth thrust and dip slip events wi thin the NW-dipping slab indicate that oceanic lithosphere, probably o riginally attached to South America, subducts to the NW beneath the Ca ribbean plate. Shallow normal faulting events E and NE of Trinidad are expressions of plate bending about near-horizontal axes parallel to t he Lesser Antilles subduction zone. We conclude that the earthquake me chanisms provide strong support for the right oblique collision model of Caribbean-South American plate interaction.