Source characterization of small to moderate earthquakes in the East Anatolian fault zone

Source characterization of small to moderate shallow earthquakes in the East Anatolian Fault Zone (EAFZ) is studied through strong motion recordings in a broadband frequency range. Following the 2020 Mw 6.8 Sivrice earthquake in the Puturge segment of the EAFZ and the 2023 Pazarcik-Kahramanmaras and Ekinozu-Kahramanmaras earthquakes with moment magnitudes of Mw 7.7 and Mw 7.6, respectively, seismicity in the region has increased significantly. Source features such as strong motion generation areas (SMGA), stress drop, and rise time of 11 moderate-sized earthquakes (5.0 < Mw < 6.8) spanning a region from the Puturge segment to the Amanos segment have been determined using the Empirical Green's Function (EGF) Method. Source parameter determination with simulations requires the optimal match between observed and simulated earthquake waveforms; however, there is a lack of consensus regarding the numerical expression for evaluating the adequacy of the fit in the EGF method. The best source parameters were identified by evaluating the average Goodness-of-Fit (GOF) based on nine different evaluation criteria, considering energy content and peak values, as well as frequency and time domain characteristics of the observed and simulated waveforms. The analyses revealed that stress drop in SMGA exhibits considerable variability, ranging from 0.75 to 22.3 MPa. It was found that small events at the southwestern tip of the Puturge segment released stress drops as high as those of moderate-size events, suggesting potential for future seismic activity. Additionally, the study evaluated the consistency of the source parameters with global self-similar scaling relationships for earthquakes of different magnitudes. The calculated SMGA is smaller than rupture area estimations for smaller events. Conversely, SMGA for larger earthquakes closely follows the combined area of the asperity trend. For this reason, this study contributes to a new region-specific Mo-SMGA relationship for the EAFZ. The rise time derived from the simulations is consistent with global source relationships, indicating that the results conform to established global scaling laws.