Earthquake Early Warning Physics: Predicting Strong Shaking in Seconds with P & S Waves

1. What is an Earthquake Early Warning (EEW) System?

Earthquake Early Warning (EEW) systems detect the initial non-destructive seismic waves and broadcast automated alerts to smartphones, trains, and power plants seconds before severe shaking strikes.

2. Exploiting Velocity Differences: P-Waves (7 km/s) vs. S-Waves (4 km/s)

When a fault ruptures underground, it emits fast compressional Primary waves (P-waves at ~6-7 km/s) followed by slower, highly destructive shear Secondary waves (S-waves at ~3.5-4 km/s). EEW algorithms detect the initial P-wave arrival and calculate the epicenter and magnitude within seconds, issuing warnings before S-waves arrive.