Evidence for a minimum 52 ± 1 km of total offset along the northern branch of the North Anatolian Fault in northwest Turkey

• We use Cretaceous faults sub-perpendicular to the NAF-N as precise offset markers.
• We provide a robust estimate of 52 ± 1 km displacement along the major NAF-N.
• We propose a total of ~ 88 ± 5 km offset along all branches of the NAF in Marmara Sea.
• Our data suggest Pliocene (3.9 Ma) inception age for the NAF in the Marmara region.
• We interpret that the Marmara Basins opened as transtensional structures.

The North Anatolian Fault (NAF) splits into two major branches in northwestern Turkey with most of the present strain accumulation and Holocene displacement being along the northern branch (NAF-N). Estimates of total offset along the NAF-N range between 4 km and 70 km in the Marmara Sea region. These different estimates lead to different interpretations on the formation of Marmara Sea basins. In this study, we use Cretaceous faults sub-perpendicular to the NAF-N as precise offset markers. Based on these faults, as well as the offset of the Middle Eocene volcanic belt, we report a minimum 52 ± 1 km cumulative dextral displacement along the NAF-N east of Marmara Sea near 31°E longitude. The displacement of the Middle Eocene volcanic belt shows that the offset is post-Middle Eocene. If we assume an additional 15 km dextral displacement on the second strand of the NAF-N (Düzce fault), the total offset along the NAF-N can be estimated as ~ 67 km in the Eastern Marmara region. Adding the published offsets that range from 16 to 26 km on the Southern Branch of the NAF give a total offset estimate of whole NAF zone as 88 ± 5 km in the eastern Marmara region. The GPS velocity estimate indicates ~ 23 mm yr− 1 of total plate motion across and near eastern Marmara Sea that would take 3.9 million years to accumulate 88 km of displacement on the NAF. Additionally, the Anatolian Plate would not have instantaneously accelerated to its modern rate of motion. Thus, initiation of transform displacement must somewhat pre-date 3.9 Ma.

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