We analyze the main and aftershocks of the June 27, 1998 Adana earthquake using data from the short-period Cilician seismograph network in order to investigate the seismotectonics of the northeastern Mediterranean region. The mainshock is found to have a pure left lateral strike-slip mechanism (strike=50¿, dip=85¿, rake=10¿, M0=3.63¿1018 Nm). The inferred strike direction of 50 ¿N closely aligns with the surface trend of the G¿ksun Fault Zone (GFZ). The depth and size of the mainshock and the distribution of the aftershocks indicate that the rupture nucleated within the lower crust, and did not extend to shallower zones. This seismicity pattern indicates that these events are associated with actively interacting African and Anatolian lithospheres in a strike-slip manner at depth. Thus, we propose that the southern segment of the GFZ belongs to the diffuse Africa-Anatolia plate boundary and plays a major role in the plate kinematics of the northeastern Mediterranean. ¿ 2000 American Geophysical Union