Seismograms from a local seismic network in the Virgin Islands portion of the northeastern Caribbean are used to determine a composite focal mechanism for 26 microearthquakes along the North America--Caribbean plate boundary. Only one nodal plane of the focal mechanism could be constrained from P-wave first motion data alone. P/SV amplitude ratios observed for these events were compared to theoretical amplitude ratios calculated for different focal mechanisms. This procedure constrained the dip of the second nodal plane to be shallower than about 50¿, ruling out the possibility of a transform fault in this portion of the plate boundary. The resulting focal mechanism indicates that oblique underthrusting of the North American plate beneath the Caribbean plate occurs in the area. This oblique motion is accommodated along a thrust plane that dips at a relatively shallow angle beneath the Virgin Islands platform.