New GPS-derived velocity field for Marmara region: Implications for the kinematics along the North Anatolian Fault Zone

The North Anatolian Fault Zone (NAFZ) is a major strike-slip fault system accommodating the relative motion between the Anatolian and Eurasian plates, extending approximately 1200 km from eastern Turkey to the Aegean Sea in the west. Despite several large earthquakes along the NAFZ during the last century, the northern strand beneath the Sea of Marmara has been seismically silent since the 1766 events, raising concerns about future seismic hazards. The ∼160-km-long seismic gap, bounded by the 1912 and 1999 ruptures, is considered to have a potential nucleation for a future M > 7 earthquake due to significant strain accumulation over the past two centuries. While previous studies have provided valuable insights into the geometry and deformation patterns of the NAFZ in the Marmara region, discrepancies remain regarding the fault coupling and slip behavior of its submarine segments. The sparse onshore geodetic data, particularly on the northern side of the fault, and limited offshore geodetic observations hinder the ability to entirely resolve fault kinematics and slip characteristics along the northern strand in the Sea of Marmara. To address these limitations, we established a high-spatial-resolution GPS network with both permanent stations and benchmarks, enabling a better understanding of the submarine segment's behavior and seismic potential by investigating the interseismic deformations along the NAFZ segments beneath the Sea of Marmara. Using the recent interseismic GPS velocities, we applied a block model inversion to estimate fault slip rates and coupling ratios along the northern strand of the NAFZ. The checkerboard tests indicate the robustness of our results. This study provides new geodetic constraints that improve our understanding of the seismic potential of the NAFZ beneath the Sea of Marmara, offering critical insights for seismic hazard mitigation in the İstanbul metropolitan area.