New <i>τ_c</i> regression relationship derived from all <i>P</i> wave time windows for rapid magnitude estimation

Abstract

Abstract Two issues related to the average period τ c early‐warning parameter are the magnitude saturation effect on large earthquakes and considerable scatter for small earthquakes. To reduce the effect of these two issues on earthquake early‐warning systems, we introduce a new τ c regression relationship derived from all P wave time windows (PTWs) in high‐pass filtered ( T = 0.075 Hz) strong‐motion data for three damaging moderate‐to‐large earthquakes. Our results show that this relationship provides a better and more stable magnitude prediction than those derived from 3 s PTW without a saturation effect on large earthquakes with M &lt; 7.5. It is expected that fewer false alerts (those outside the magnitude uncertainty tolerance) would be issued. Additionally, a reduction of the initial PTWs to 1–2 s and evolutionary calculation with an expanding window allow more lead time for small‐to‐moderate events.