Slip asymmetry of the Yedisu Segment of the North Anatolian Fault from GPS velocity fields

The Yedisu Segment is one of the most significant seismic gaps of the North Anatolian Fault Zone (NAFZ), following the segments located near Istanbul. This segment is approximately 80 km long and has remained seismically quiet for about 242 years. It has the potential to generate an earthquake magnitude of greater than Mw 7. The Tercan and Nazımiye dextral faults are located in the vicinity of the Yedisu Segment and exhibit similar strikes of approximately N70–75°W. In this study, slip rates and locking depths of the Yedisu Segment and its neighboring Tercan and Nazımiye faults are estimated by inverting GNSS-derived Eurasia-fixed velocity fields using elastic half-space dislocation models. Velocities from Turkish Real-Time Kinematic GNSS Network (CORS-TR, including a few older stations), Turkish National Fundamental GPS Network (TNFGN), and previously published regional GNSS networks are used, and the inversions are performed using fault-parallel velocity components while accounting for differences in fault strike. Two different forms of elastic half-space dislocation model are tested for the Yedisu Segment: (i) symmetric and (ii) asymmetric fault-slip behavior. The symmetric model yields a Yedisu slip rate of approximately 18.7 mm/yr, while the Nazımiye and Tercan faults contribute only minor deformation to the regional velocity field. The asymmetric model conversely discloses a difference between the south- and north-side of the Yedisu Segment, with slip rates of about 6.5 and 11.9 mm/yr, respectively. The fault slip rate asymmetry correspondes to a ratio of 1.83. The asymmetric model explicits a significantly better fit to the GNSS velocity field than the symmetric approach. Assuming a long-term average slip rate of 18.4 mm/yr, the Yedisu Segment has accumulated approximately 4.45 m of slip deficit over the past 242 years, consistent with the potential for a large, destructive earthquake. These results indicate that the Yedisu seismic gap is highlighting its critical importance for seismic hazard assessment in eastern Türkiye. This research is supported by the TÜBİTAK project No. 124Y204.Keywords: North Anatolian Fault, Yedisu Segment, GNSS, Fault slip asymmetry, Seismic gap