That's correct about Japan already having this technology. It was quite necessary given their use of some of the highest-speed trains in the world. These trains will stop immediately upon getting the signal from the early warning system.

Japanese researchers found that there are 'P-waves' that precede the more damaging waves, which they used to create this early warning system, made up of thousands of seismometers placed throughout the country. Chile hopes to use this same technology for their own public safety.

https://en.wikipedia.org/wiki/Earthquake_Early_Warning_(Japa...