Seismological and Geodetic Insights on the North Anatolian Fault Zone through Coda Calibration and InSAR Techniques

The North Anatolian Fault Zone (NAFZ) is a region of high seismic risk and significant tectonic complexity. In such regions, different magnitude scales provide complementary insights into the physical properties of seismic wave propagation. However, achieving reliable seismic hazard assessment remains challenging due to non-homogeneous magnitude reporting and the potential bias introduced by linking short-period magnitudes (M_L​) to moment magnitude (M_w). To address these inconsistencies and improve source characterization, this study presents an integrated seismological and geodetic framework. Our primary objective is to develop a robust, homogeneous M_w​ catalog focusing on events ranging from M_w​ 3.5 to 6.0. To achieve this, we employ the Coda Calibration Tool (CCT), applying the empirical envelope-based method developed by Mayeda et al. (2003). Unlike traditional direct wave analysis, this method utilizes the stable, scattered energy of coda waves to effectively mitigate path and site effects caused by lateral heterogeneity in the crust across diverse tectonic settings. By constraining the calibration with independently derived M_w​ from moment tensor inversion for low frequencies and apparent stress (σ_A​) for high frequencies, we successfully lower the threshold for reliable M_w​ and radiated energy estimation. Moreover, we validate this seismological approach by conducting geodetic modeling for two significant events: the 23 November 2022 M_w​ 6.0 Düzce and the 18 April 2024 M_w​ 5.6 Tokat earthquakes. We perform Interferometric Synthetic Aperture Radar (InSAR) analysis using pre- and post-earthquake ascending and descending Sentinel-1 images to create a coseismic deformation map, invert using Okada elastic dislocation modeling to obtain source parameters such as fault slip distribution, and then calculate M_w. The results demonstrate remarkable consistency between M_w values derived from CCT and InSAR. Furthermore, our analysis reveals evidence for non-self-similar source scaling in the NAFZ. We observe that σ_A​ increases with seismic moment (M₀​), suggesting that larger earthquakes radiate energy more efficiently. Additionally, the apparent stress estimates are systematically lower than in other active tectonic regions, indicating a potentially low-seismic-efficiency environment. This multi-physics framework thus produces a homogeneous catalog for refining seismic hazard assessments and provides fundamental new insights into the rupture physics of the NAFZ.