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More recent Caribbean GPS research GPS Investigation of the
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Principal Investigators: Low-Cost Collaborators: Start/Finish Dates: 1994- TECTONIC OVERVIEW AND OUTSTANDING PROBLEMS  The Caribbean region has long been recognized as a classic locality for studying active strike-slip and subduction processes in a largely submarine setting (Fig. 1A). The geologic structures that separate the Caribbean plate from the North American plate consist of a 2000km-long series of faults that connect the Lesser Antilles trench in the east to the Middle America trench in the west (Fig. 1B). The plate motion that occurs across these faults appears to be predominantly left-lateral in an east-west direction, with some possible N-S convergence (see Mann et al. [1990] for a compilation of fault and other geologic data pertinent to the presentday defommation). The plate boundary located west of the Cayman Trough (Fig. 1B) is a more or less single, continuous strand except in Central America where there are complexities associated with its passage through older orogenic belts and its intersection with the Middle America trench. In contrast, the plate boundary located east of the Cayman Trough is more complex and consists of at least two sub-parallel fault strands sub-parallel to the plate boundary, and numerous faults that segment the arc. These faults are postulated to bound one or more microplates, whose existence is suggested by teleseismic information (Figs. 2A and 2B) and onland and marine geologic survey [Sykes et al. 1982; Rosencrantz and Mann, 1991; Byme et al., 1987]. The existence of microplates along the northeastem Caribbean-North America plate boundary and implied absence of a discrete boundary may explain why the Caribbean plate has been a weak link in models for present-day plate modons. Models for the present-day motion of the Caribbean relative to the adjacent Cocos, North and South American plates rely heavily on kinematic data from the Caribbean-North America plate boundary [Jordan, 1975; Sykes et al. 1982; Stein et al. 1988; DeMets et al. 1990]. However, if deformalion along the plate boundary is controlled by the movement of microplates or by slip along closely spaced faults that approximate fluid flow between the two plates, any kinematic data from the northeastem Caribbean plate boundary are likely to be biased relative to the true Caribbean-North America velocity. Difficulties in selecting kinematic data that accurately reflect Caribbean plate motion have lead to kinematic models that predict a wide range of Caribbean-North America rates anddirections, from 12-37 mm yr-1 of E-W strike-slip motion to NE-directed convergence. None of these models predict all of the geologic and seismic observations compiled from the plate boundary zone [Heubeck and Mann, 1991]. Because kinematic data from the circumCaribbean plate boundaries are also used to derived global plate motions models, lhe NUVEL1 model (as well as its predecessors) has probably been adversely affected [DeMets, 1993]. The lack of a widely accepted, accurate model for Caribbean plate motions has complicated efforts to test altemative geological models for Caribbean tectonics, and in general has hindered a deeper understanding of the present and past geological evolution of the Caribbean region. We believe that a number of important topics and testable models could be examined if aufficiently accurate measurements of motion across the Caribbean-North America plate boundary were available. These include
The accumulation of unanswered questions and testable models presents an extraordinary opportunity for geodetic measurements to make an important scientific contribution to our understanding of circum-Caribbean and global tectonic, and ultimately, the process of arc fragmentation and continental accretion. What is required to test these models and questions is clear accurate measurements of Caribbean site velocities in a fixed North America reference frame. We believe that the time is ripe for this investigation for the following reasons:
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