Learning from the First Seconds: P-Wave-Based Moment Magnitude Estimation in the Marmara Sea Region

The initial seconds following an earthquake provide vital information for rapid magnitude estimation, supporting real-time early warning efforts. This study evaluates the determination of P-wave moment magnitude (M _wp ) using strong-motion records from the April 23, 2025, Marmara Sea earthquake. High-quality accelerometric data from the Turkish National Strong Motion Network were analysed to extract early P-wave features within the first 3 s after P-wave onset. Results demonstrate notable directivity effects for stations located along the eastern Marmara segment of the North Anatolian Fault. The mean M _wp was calculated as 6.5 ± 0.2, consistent with GCMT estimates. Magnitude estimation was achievable within 8–20 seconds of P-wave arrival, confirming the method’s real-time applicability. Our findings demonstrate that strong-motion P-wave analysis can provide fast and reliable magnitude estimates suitable for integration into earthquake early warning systems in densely populated and industrialised regions, such as Istanbul and the broader Marmara area.