The tech here is P-wave detection. P-waves are somewhere around twice as fast as S-waves, so if you're 100-200km away from the hypocenter, it gives you that much advanced warning. Powerful earthquakes are still destructive at that range.
The other advantage is that once the seismic wave is detected, you can transmit that info at lightspeed vs the 10s of km/h that seismic waves propagate.