Three multichannel seismic profiles imaged a normal fault to at least 10 km depth in the North Aegean Trough and Thermaïkos basin. The fault is active and recent, forming a scarp at sea bottom and crossing the Quaternary deltaic front on the northern slope of the trough controlled to the south by the North Anatolian fault. Prestack depth migration imaged the fault as a seismic reflector cutting steeply across the sedimentary rocks and flattening in the basement. From the seismic image, the N100°E strike of the fault scarp, and the orientations of the three profiles, the true fault dip is constrained to an average 20° in the basement, a low-angle dip. The throw and age estimated from the geometry in the sedimentary rocks document recent onset of the motion that must have occurred at a high rate. Both the direction and the rate of slip are consistent with the instantaneous motion as measured by space-based geodesy, which shows the fault to be forming by pure normal slip. Large earthquakes that have occurred in the basin may relate to such normal faults, whereas the North Anatolian fault with its current strike-slip earthquakes appears to slip here under low resolved shear stress.