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Abstract

Earthquake source parameters provide key diagnostic observations to quantify the seismogenic environment and understand earthquake physics. Among them, earthquake stress drop plays an essential role in impacting the frequency content of ground motion. Accurate stress‐drop estimation is conditioned on data quality, appropriate modeling of propagation effects, and selection of the source model and inversion techniques. One way to evaluate reliability of stress‐drop assessments is to compare results combining different methodologies and assumptions. In this study, we calculate earthquake source parameters for micro‐ to moderate earthquakes in the Sea of Marmara region, northwestern Türkiye, where the Main Marmara fault encompasses a spectrum of slip behaviors from creeping to locked. We apply two approaches: (1) a spectral fitting approach to constrain the corner frequency, seismic moment, and quality factor, and (2) a nonparametric spectral decomposition approach to isolate source spectra from propagation and site effects. We then estimate the earthquake stress drop using a Brune source model. This leads to source parameter estimates for 1577 and 1549 earthquakes with (1.0–5.7) for the spectral fitting and spectral decomposition approaches, respectively. Despite the fundamental differences in methodologies, results from both methods are consistent, particularly in highlighting relative differences within the dataset. Small but statistically significant spatial stress‐drop variations are observed along different fault segments of the Main Marmara fault. In particular, lower average stress drops are observed in fault segments partially releasing slip aseismically, with the lowest values observed surrounding earthquake repeaters, which may imply a weaker fault in the creeping region. The M ≥ 5 earthquakes along the Main Marmara fault within the last decade were not followed by significant changes in the stress drop, suggesting no significant reduction of fault stress level or fault strength due to their occurrence, supporting the presumably high stress level on this fault.