Seismicity Parameters of the Westernmost Part of the North Anatolian Fault Zone (NAFZ)

This study characterizes seismicity and stress regime in the westernmost part of the North Anatolian Fault Zone (NAFZ), focusing on the Saros segment, where dextral strike-slip deformation transitions into the transtensional northern Aegean domain. Unlike previous regional studies that combine Marmara and broader Aegean datasets or focus on individual rupture sequences, this study isolates a coordinate-bounded transition window to quantify the intrinsic seismic behavior of the terminal NAFZ–North Aegean Trough (NAT) linkage zone within a completeness-controlled framework. A December 1917–September 2025 earthquake catalog was compiled and homogenized to local magnitude (ML). Completeness analysis yields a reference Mc ≈ 3.2, consistent with Gutenberg–Richter statistics. Recurrence and annual probability metrics were evaluated for 1917–2025, 1985–2025, and 2010–2025 to assess temporal stability and completeness-related effects in seismic productivity. Recurrence and frequency–magnitude characteristics of the non-declustered and declustered catalogs were compared to assess aftershock effects on seismic rates. For events with M ≥ Mc, the estimated parameters are b = 0.91 ± 0.05 and a = 5.392 indicate moderate seismic productivity. Focal mechanisms and stress tensor inversion indicate a dominant dextral strike-slip regime with subordinate N–S extension, confirming a transtensional stress field linking the Saros region to the northern Aegean. Integrated completeness-controlled seismicity statistics and stress-tensor inversion show that the Saros segment functions as a transform–transtensional linkage corridor rather than a discrete tectonic boundary, refining the seismotectonic framework of the Marmara–Saros–North Aegean transition zone and providing robust parameters for seismic hazard and fault-segmentation analyses.