Seismic Hazard Potential in and around the Yedisu Seismic Gap: Implications from Seismological and Geodetic Constraints

Türkiye is known as one of the most seismically active regions in the world due to its rapidly deforming tectonic properties that has been developed by the northward movement of the African and Arabian plates relative to the Eurasian plate. These plate movements caused the Anatolian plate to be compressed in the east and move westward, resulting in the formation of the most important tectonic structures in the region, the North Anatolian Fault Zone (NAFZ) with ∼1500 km length and right-lateral strike-slip motion in the east-west direction, and the East Anatolian Fault Zone (EAFZ) with ∼700 km length and left-lateral strike-slip motion in the northeast direction.  Historical records show that seismic energy release along the NAFZ migrated westward with large earthquakes, i.e., the 1939 Erzincan earthquake (Mw7.9), 1942 Erbaa-Niksar earthquake (Mw7.0), 1999 İzmit earthquake (Mw7.4), and 1999 Düzce earthquake (Mw7.2). However, two significant seismic gaps exist throughout the NAFZ; Marmara and Yedisu. We, in particular, examined the Yedisu Seismic Gap (YSG) in this study, by investigating the interrelationships between seismicity, Coulomb stress changes, seismotectonic b-values, and surface deformation with the aim of understanding the characteristics and seismic hazard potential in and around the YSG. More specifically, we analyzed the seismic activity of the eastern NAFZ extending from the Erzincan basin to the Karlıova Triple Junction (KTJ) using earthquake catalogs from 1900 to 2024, which include both Mw≥1 earthquakes and Mw≥4 earthquakes. 3D Coulomb stress change behavior was compared with the background seismicity pattern in the region. We further performed a joint interpretation of lateral variation of statistical b-values, seismic P- and S-wave speeds, and InSAR-based surface deformation in order to understand possible regions of asperities or high pore-pressure where the accumulated stress often released due to the decreasing normal stress on the fault. Our preliminary results indicate that the stress has been transferred to the YSG following the 14 June 2020 Mw5.7 Karlıova earthquake. The results of our multi-data analysis will provide invaluable insight into the current seismic hazard potential of the YSG, which will be essential for future urban planning in this region.