When a strong earthquake strikes, every second matters. Situated on the Ring of Fire, Taiwan experiences approximately 40 thousand earthquakes per year on average, among which 1,000 can be felt. It is impossible to predict when an earthquake will hit. But now, thanks to the earthquake early warning (EEW) system developed and improved by the Central Weather Administration (CWA), people are able to receive warning messages before intense shaking occurs and seize the golden seconds to find shelter, reducing casualties and losses.

       It is not difficult to understand how EEW works. When an earthquake occurs, two kinds of shock waves will be sent simultaneously from the epicenter: Pwaves (longitudinal waves) and S-waves (traverse waves). P-waves travel faster and cause perpendicular vibrations in the ground. S-waves, though travelling slower, rock the ground side-to-side and are the main cause of serious damage. P-waves generally    (49)   faster than S-waves. Therefore, if seismic stations can accurately detect P-waves and quickly measure the intensity, for earthquakes with magnitude of 5.0 and above and estimated intensity of at least 4, warnings can be sent to people before they feel the shake.

     The CWA has been working to accelerate EEW and reduce blind zones. Before 2017, it took the EEW system 17 seconds from detecting P-waves to sending warnings, and it had a blind zone around epicenter with a 60-km radius. After 3 years of effort and improvement, the time was shortened to 10 seconds, and the radius of the blind zone shrank to 35 km. The system then has been further improved with machine learning. The time can be reduced to 7 seconds and the radius to 25 km. If the epicenter is in the 6 most populated cities in Taiwan, the people can receive warnings even faster with an even smaller blind zone.