Japan can now detect earthquakes 20 seconds before they hit land. Thanks to an undersea 'nervous system'

Japan has become the first country to cover every inch of the faultlines that trigger earthquakes in the country with sensors and cables connecting to hundreds of observatories to ring the alarm long before the first tremors hit. This ocean-floor "Nervous System" will detect the minutest signs of an earthquake and a tsunami. Scientists say that it will send out a warning about an earthquake 20 seconds before it occurs, and 20 minutes before a tsunami. This warning system will leave emergency teams with more time to send alerts and evacuate people before disaster strikes. Steps could be taken to prepare the infrastructure to brace for the impact. Japan is now the first country that can directly monitor entire subduction zones in real-time. Seismologist Harold Tobin, director of the Pacific Northwest Seismic Network, says the network is more than just an advanced warning system, Scientific American reported.

Japan started expanding its earthquake-detection system to cover the ocean floor after the 2011 earthquake that killed nearly 20,000 people. The magnitude 9.0 “megathrust” earthquake was the worst temblor in the history of Japan. It rattled the region for six minutes and triggered a 130-foot tsunami travelling at speeds of 700km/hr. The alerts were delayed, and the tsunami warning failed to gauge the real havoc it could cause. People had as little as 10 minutes to evacuate. The Great East Japan Earthquake started in the ocean 72 kilometres off the shore. Land sensors picked up the seismic waves but had no idea how huge it was and how massive the tsunami waves could be. Also Read: Nankai Trough 'megaquake' could kill 300,000 people: Japan acknowledges risk, ramps up measures

Japan has wired offshore fault zone

Japan realised it had a blind spot - the ocean. So it decided to expand its earthquake detection system to the ocean. Tobin says, "By wiring up the offshore fault zone, we’re constantly able to listen to it. That means we can detect all sorts of subtle signals that tell us how faults work, such as the storage of stress and how it starts to be released at the beginning of an earthquake." The system has been completed in parts, with the first one finishing in 2017. The S-net (Seafloor Observation Network for Earthquakes and Tsunamis) wired the nation’s earthquake-detection network to the Japan Trench, the point where the 2011 quake began. It comprises 5,700 kilometres of cables covering 116,000 square miles of ocean, connecting to 150 observatories on the ocean floor. Seismometers, accelerometers, and pressure gauges measure the waves. In 2018, a magnitude 6 quake struck Japan, and alerts reached the city 20 seconds before the seismometers on land detected it. Also Read: Is an underwater volcano getting ready to erupt in Andaman? Warning issued as dozens of earthquakes rock Thailand, Myanmar and Nicobar

Nankai Trough earthquake warning

In 2019, Japan started N-net (Nankai Trough Seafloor Observation Network for Earthquakes and Tsunamis), which is now complete. It covers a crucial subduction zone where the last major quake happened in 1946. A report has warned that a megaquake could hit the region in the next 30 years and kill up to 300,000 people, and result in damages worth $2 trillion. The Nankai Trough is a roughly 800 km undersea trench and a subduction zone where the Philippine Sea Plate is being pushed beneath Japan. The Nankai Trough was recently in the news because of a 1999 manga comic that predicted a devastating earthquake and tsunami even worse than the 2011 event on July 5.