Magnitude determination for Earthquake Early Warning using P-Alert low-cost sensors during 2024 Mw7.4 Hualien, Taiwan earthquake

Magnitude determination in earthquake early warning (EEW) systems remains a significant challenge. On April 2^nd, 2024, a Mw 7.4 earthquake struck the Hualien area in Taiwan. The Central Weather Administration (CWA) EEW system estimated the magnitude at 6.8 just 15 seconds after the earthquake. As a result, no warning alerts were issued for the Taipei metropolitan region, which experienced an intensity level of 5 lower on the CWA’s intensity scale. The lack of warning alerts sparked widespread complaints and discussions, as many residents in affected areas expressed concern over the effectiveness of the current EEW system. This study aims to compare the parameter cumulative absolute absement (CAA) with the currently used parameters, the peak vertical displacement (Pd) and the average period (τc), for quick magnitude estimation in the April 2^nd, 2024, earthquake using low-cost sensors. Results indicate that the  Pd parameter provides a closer estimate to the final local magnitude reported by the CWA; however, it carries higher uncertainty, which may present challenges for practical applications. In contrast, the CAA parameter delivers more stable estimates with smaller uncertainties. Notably, the northward rupture of this earthquake resulted in significant overestimation when using only northern stations and underestimation when using only southern stations. This underscores the critical importance of proper station distribution for accurate magnitude estimation. This underscores the critical importance of proper station distribution for accurately determining magnitudes of large earthquakes. Interestingly, the τc parameter demonstrates less sensitivity to rupture directionality, suggesting its potential robustness in such scenarios.