On March 24, 1978, a magnitude 6.0 intraplate earthquake occurred 380 km southwest of Bermuda near magnetic anomaly M4 (≈118 m.y.B.P.). A catalog of seismicity for the Bermuda rise indicates that this is an area of significant intraplate seismicity in the western North Atlantic Ocean. The fault plane solution for the 1978 event is of thrust type and strikes 340¿, in an intermediate direction to the trends of major fracture zones (300¿) and abyssal hill topography (035¿) in the area. The P axis of this mechanism is nearly horizontal and trends 259¿, subparallel to the absolute plate motion vector for North America. Aftershock activity was detected teleseismically for approximately 8 months after March 24, and the entire sequence is best described as a prolonged mainshock-aftershock series. During June 18--28, 1978, we conducted a microaftershock survey of the area using ocean bottom hydrophones and recorded 250 events (0b<2). These smaller events are located in a tight cluster 5--10 km northeast of the NEIS mainshock location. SP-P data from microaftershocks recorded during this survey indicate a relatively narrow band of activity (about 10 km wide), smaller than would be inferred based on NEIS aftershock locations alone. Many of the recorded microaftershocks exhibited prominent water wave phases, which have been used to constrain further the epicentral locations. The depths of these events, while not well determined, appear to be shallow, i.e., less than 5 km below the seafloor. Estimates of the b value, determined from two instruments for the 10-day recording period, are 1.10¿0.30 to 1.50¿0.60. Overall, both the fault plane solution and subsequent aftershock locations of the 1978 event suggest that faulting did not occur along a major oceanic fracture zone but, rather, along a smaller-scale feature within the M11-M4 spreading discontinuity. The spatial clustering of seismicity near the perimeter of the rise suggests that variations of crustal thickness associated with the Bermuda rise may be responsible for triggering intraplate seismicity in this region.