Previously Unrecognized Now-Inactive Strand of the North Anatolian Fault in the Thrace Basin

Dogan Perincek

The North Anatolian fault is a major 1,200 km-long transform fault bounding the Anatolian plate to the north. It formed in late middle Miocene time as a broad shear zone with a number of strands splaying westward in a horsetail fashion. Later, movement became localized along the stem, and the southerly and northerly splays became inactive. One such right-lateral, now-inactive splay is the west-northwest-striking Thrace strike-slip fault system, consisting of three subparallel strike-slip faults. From north to south these are the Kirklareli, Luleburgaz, and Babaeski fault zones, extending ±130 km along the strike. The Thrace fault zone probably connected with the presently active northern strand of the North Anatolian fault in the Sea of Marmara in the southeast and m y have joined the Plovdiv graben zone in Bulgaria in the northwest.

The Thrace basin in which the Thrace fault system is located, is Cenozoic with a sedimentary basin fill from middle Eocene to Pliocene. The Thrace fault system formed in pre-Pliocene time 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. Releasing bend extensional structures (e.g., near the town of Luleburgaz) and restraining bend compressional structures (near Vakiflar-1 well) are abundant on the fault zones. Umurca and Hamitabad fields are en echelon structures on the Luleburgaz fault zone.

The Thrace strike-slip fault system has itself a horsetail shape, the various strands of which become younger southward. The entire system died before the Pliocene, and motion on the North Anatolian fault zone began to be accommodated in the Sea of Marmara region. Thus the Thrace fault system represents the oldest strand of the North Anatolian fault in the west.

AAPG Search and Discovery Article #91032©1988 Mediterranean Basins Conference and Exhibition, Nice, France, 25-28 September 1988.