Inclusion of a novel site specific soil parameter in early warning algorithm for the enhanced earthquake magnitude prediction

Earthquake early warning (EEW) systems rely on rapid and accurate magnitude estimation from early P-wave signals, commonly using peak displacement amplitude (Pd). However, Pd-based magnitude prediction is strongly influenced by local site conditions, which are often neglected in conventional models. This study introduces a site-specific soil parameter, PGV/Vp30, where PGV is the peak ground velocity measured from the first three seconds of the vertical P-wave component and Vp30 is the average P-wave velocity in the upper 30 m of the subsurface. The parameter is integrated into linear empirical relationships for Pd and magnitude estimation and evaluated using 2317 strong-motion records from the Japanese KiK-net network. Results show that incorporating the site-specific parameter improves Pd prediction stability by 43% and reduces the uncertainty of average magnitude error by 48%. The proposed model also reduces magnitude underestimation for large events (M > 7.0). Validation against empirical models from Southern California and Taiwan confirms the robustness of the approach. These findings demonstrate that incorporating site-specific soil response significantly enhances the accuracy and reliability of EEW magnitude prediction.