The North Anatolian fault is a 1200-km-long major transform fault bounding the Anatolian plate on its north side. The fault formed during the late middle Miocene as a broad shear zone with a number of strands splaying westward in a horsetail pattern. Later, movement became localized along a central strand, and the southerly and northerly splays became inactive. The west-northwest-striking Thrace strike-slip fault system is one of these right-lateral, presently inactive, splays. It consists of three subparallel strike-slip faults. From north to south these are the Kirklareli, Luleburgaz, and Babaeski fault zones, which extend for about 130 km through the Thrace basin. The Thrace fault zone probably connected to the southeast with the presently active northern strand of the North Anatolian fault in the Marmara Sea. To the northwest, the zone may have extended to the Plovdiv graben zone in Bulgaria.

The Cenozoic Thrace basin contains middle Eocene to Pliocene sedimentary rocks. The Thrace right-lateral wrench fault system formed prior to the Pliocene and had become inactive by the Pliocene. Strike-slip fault zones with normal and reverse separation are detected by seismic reflection profiles and subsurface data. As the system became inactive, the motion on the North Anatolian fault zone began to be accommodated in the Marmara Sea region. Thus, the Thrace fault system represents the oldest strand of the North Anatolian fault to the west of Istanbul. Releasing-bend extensional structures and restraining-bend compressional structures are abundant along the fault zones. Several hydrocarbon-producing anticlines lie en echelon to the Luleburgaz fault zone. Regionally, the Thrace fault ystem has a horsetail shape, with the various strands becoming younger southward.