eraexplainer on Instagram: "During a live stream, a Japanese creator received an earthquake alert before the shaking started. Japan uses a nationwide network of thousands of seismic sensors that detect fast P-waves, which arrive before the stronger, damaging S-waves. Within seconds, the system estimates location and intensity and sends alerts to phones, TVs, trains, and public systems—giving people crucial seconds to react, stop trains, slow elevators, and reduce injuries. Preparedness + real-ti