Performance of the P-alert real-time shakemaps system and onsite warning during the 2025 ML6.4 Dapu earthquake

Abstract

Abstract On January 20, 2025, the ML6.4 Dapu earthquake struck southwestern Taiwan, causing intense shaking in Chiayi County and Tainan City. The P-Alert real-time shakemaps system generated detailed shakemaps just 36 s after the earthquake occurred. The areas of strongest shaking were primarily located to the southwest of the epicenter, which corresponds with the observed damage distribution. Based on the epicenter location, the distribution of shaking, and the distribution of aftershocks, it is likely that the rupture propagated southwestward from its initiation point. For this event, the Central Weather Administration (CWA) issued the first report 7.9 s after the earthquake occurred. Considering the average signal transmission delay of approximately 5 s in the Public Warning System (PWS), most individual P-Alert devices located within 30 km of the epicenter provided onsite warnings earlier than the CWA’s regional warning. These observations underscore the effectiveness of the P-Alert system in providing onsite warnings, as well as its significant advantages in disaster response.

Keywords

• Damage earthquake
• Shakemaps
• Earthquake early warning
• Peak ground acceleration
• Peak ground velocity