What is a megaquake and how is Japan predicting one? All about the Earthquake Early Warning system
Japan has issued its first megaquake warning since the launch of the new Earthquake Early Warnings System in 2022. The system triggers an alert for a much bigger earthquake following a magnitude 7 or higher temblor. The warning is effective for at least a week.
Megaquake warning issued in Japan
Japan was hit by a 7.5 magnitude earthquake on Monday (December 8). Authorities warned of further aftershocks and asked people to stay alert. On Tuesday, it issued its first official warning for a megaquake, a massive temblor that can trigger large tsunamis and cause widespread devastation. Here is all you need to know about it.
What is a megaquake?
A megaquake is an extremely powerful earthquake that measures magnitude 8.0 or greater. Such an earthquake could trigger massive tsunami waves and destroy infrastructure on a large scale. It was the first time Japan issued a top-tier alert since the launch of a warning system in 2022. This system was put in place to detect the likelihood of a big one hitting the country.
Japan's Earthquake Early Warnings System
Japan has had an early warning system in place since around 2007, as per the Japan Meteorological Agency (JMA) website. The agency provides residents in Japan with Earthquake Early Warnings, sending alerts just as an earthquake starts. It also tells about the expected intensity of an earthquake and the time it is likely to hit.
Earthquake Early Warning system was updated in 2022
This system was updated in December 2022 by the Headquarters for Earthquake Research Promotion (HERP) and the JMA. It has a Japanese name, which in English roughly translates to "Hokkaido–Sanriku-offshore Aftershock Earthquake Alert Information".
New warning system is triggered when a magnitude 7.0 earthquake has already struck
It is a new "foreshock-based alert" system put in place for potentially large mega-earthquakes, those that are magnitude 8.0 or greater in northern Japan. The system is triggered when a magnitude 7.0 or higher earthquake has already occurred in key subduction zones, such as the Japan Trench or Chishima Trench.
Warning system sends alerts asking people to be prepared
After it is triggered, it sends out warnings to people in the region to prepare for a massive earthquake, or a megaquake. They are advised to prepare for quick evacuations and keep certain things handy. On Tuesday, people were told to review local evacuation routes, gather emergency supplies, secure heavy items inside the home, and make sure they have enough food, water, and portable sanitation for several days.
New earthquake warning system predicts a much larger “mainshock”
The main idea behind the new warning system is to prepare for a much larger “mainshock” after a strong foreshock. To forecast a megaquake several hours and days before it hits gives ample time to prepare for a major seismic event. This is why the new system is said to be launched in 2022. Notably, the system issues only a precautionary warning, and there is no certainty that a megaquake will strike.
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