Summary Moment magnitude (Mw) is a widely accepted magnitude scale as a direct physical measure of the long-period seismic energy released at the foci, and thus its reliable quantification is of great importance for accurate probabilistic seismic hazard assessment (PSHA) studies. Yet, a robust estimation of Mw and radiated energy (ER) over a wide range of magnitudes is difficult, mainly due to the existing strong lateral heterogeneous nature of the crust. Furthermore, converting short-period magnitudes such as local magnitude (ML) to Mw can often lead to significant bias. To address this issue, we employ a coda envelope-based source spectral method, which depends on a regional empirical calibration approach that can lower the threshold for reliable Mw and ER estimates. To achieve this aim, we analysed horizontal component waveforms recorded at broadband stations operated by the Kandilli Observatory and Earthquake Research Institute and the Disaster and Emergency Management Presidency from 51 selected moderate local and regional earthquakes (ML ≥ 4.0) that occurred between 2013 and 2024 in and around the central North Anatolian Fault Zone (CNAFZ), including the 23 November 2022 Mw 6.0 Düzce and the 18 April 2024 Mw 5.6 Tokat events. The Java-based Coda Calibration Tool (CCT) implemented on these waveforms enabled a successful establishment of the coda-derived source spectrum that allowed us to obtain robust estimates of apparent stress (σA) and Mw across the CNAFZ. Following the calibration with reference events, we extend reliable magnitude estimation to smaller earthquakes (3.5 ≤ ML 4.0), confirming robust predictions. Beyond providing a more thorough event catalogue in the CNAFZ, our results reveal low σA levels, comparable to those reported in recent studies in the Marmara Sea, and indicate non-self-similar rupture behaviour that may improve future regional seismic hazard assessments. This approach may also serve as a framework for reliable small-to-moderate earthquake analysis in other tectonically active regions in Türkiye, thereby supporting broader seismic risk management efforts.
Tekiroğlu et al. (Tue,) studied this question.