Japan’s Earthquake Early Warning System

Japan has a well-developed public warning system to alert its population to the possibility of strong shaking from earthquakes. The system is automated and includes tsunami warnings.

Saturday, 16th September 2017

Japan has had an automated earthquake early warning (EEW) system since October 2007. The system uses more than 4,000 seismometers spread across Japan to monitor for the arrival of ground waves generated by an earthquake. As soon as two stations detect the fast-moving P-wave from an earthquake the system begins calculating the likely shaking intensity of the slower S-waves, the location of the quake and the locations most likely to experience shaking from the earthquake. This graphic from Japan Meteorological Agency shows how the network gathers its information.

In New Zealand, we use the Modified Mercalli system to determine ground shaking from an earthquake, but Japan uses its own system. If shaking is likely to reach the Japan seismic scale of “5 lower” an automatic public alert is issued.

The alert is automatically inserted into the television and radio broadcasts of participating networks. It consists of two chime tones, followed by the standard EEW warning, “Kinkyū Jishin Sokuhō desu. Tsuyoi yure ni keikai shite kudasai.” which translates as, “This is an Earthquake Early Warning. Please prepare for powerful tremors.” In the case of television, a graphic will appear on the screen showing where shaking is expected to occur – the graphic dynamically updates as more seismic stations report into the system.

A further enhancement has allowed tsunami alerts to be inserted into the broadcast, but these take longer to calculate and arrive minutes after the ground shaking has occurred.

The system has been enhanced to include SMS alerts to mobile devices and in-house alarm units from a number of private providers which provide warning sounds, messages, and flashing lights.

For those people nearest to the epicentre of a large earthquake, the system may provide little or no warning of strong shaking but, as distance from the epicentre increases, the system allows time for people to take cover, avoid tall cabinets, decide not to enter elevators, pull over to the side of the road or take other appropriate action. Commercial users are able to slow trains, reconfigure power stations and grids, have cranes lower dangerous loads and take other evasive action.

However, in a country that has experienced eight magnitude 6 earthquakes, 13 magnitude 7 quakes, two magnitude 8 and one magnitude 9 earthquake since 2005 (that’s 24 significant earthquakes!) a few seconds’ warning counts.

On the afternoon of the 11th of March 2011 a magnitude 9.1 earthquake struck off the coast of Japan. 8.6 seconds after detecting the incoming P-wave from the quake, the EEW had issued a public warning to prepare for powerful tremors (UC Berkeley report), just as the terrible damaging shaking started on land nearest the earthquake epicentre. This has become known as the Tohoku earthquake which caused so much damage and death from the ground shaking and subsequent tsunami. The early warning system undoubtedly prevented the staggering death tolls that have occurred from earlier earthquakes of such massive size.

This short documentary from NHK shows how the alert was flashed to the public in real time. On that afternoon, national television network NHK was broadcasting a live debate of the Parliamentary Audit Committee. The general alert with a warning for northern Japan appears on screen 31 seconds after the earthquake occurred while the parliamentarians continue their discussions, and shows how much warning the public had before strong shaking began in Tokyo. Within another 26 seconds the graphic is able to be updated with detail of where strong shaking is likely to be felt.

Shaking began in Tokyo 1 minute and 50 seconds after the quake occurred and, by then, NHK was able to place a presenter in front of the camera to provide more information as events unfolded less than two minutes after the quake struck. The documentary also shows that a projection of tsunami risk was able to be flashed to the viewers just four minutes after the earthquake had been detected. One minute later specific tsunami warnings in multiple languages were able to be broadcast.

In its first few years of operation, reviews of the EEW had an astonishing 75% to 82% success rate for successfully detecting damaging earthquakes. The system had been calibrated for the environment around Japan at the time. However, after the crippling magnitude 9.1 Tohoku earthquake, the system’s performance dropped to 56% as it worked within an environment which included five magnitude 7 events in various locations during 2011. During this time there was one event in which a major alert was erroneously generated and, whilst largely suppressed by manual intervention, a significant alert was still broadcast on some mobile devices.

Since 2011, Japan has experienced a quick drop-off of strong nearby seismic activity almost to conditions that existed before the massive earthquake of 2011. Recalibration of EEW in this new environment is continuing.

Nevertheless, EEW continues to broadcast warnings of possible serious earthquake shaking. During the Tohoku aftershock sequnce a steely television anchor smoothly reacted to an alert of one of the magnitude 7 aftershocks. She calmly disengaged her lively studio guest and began filling-in specific local shaking warnings while the automated warning was on-screen. As the event unfolded, the studio was reconfigured around her as she read from prepared notes and data being supplied by the EEW system. By the time the studio began shaking, the broadcaster had managed to get sufficient information up on the teleprompter for her to continue her work. This film clip also shows the automated tsunami warning being triggered with the alert being broadcast in several languages as the tsunami warning map is progressively populated with estimates of wave heights.

As Japan’s EEW works through this post-magnitude 9 phase, it is presenters like this and our own steely Vicki McKay who heroically remain calm as they sit in their broadcasting studios. Vicki McKay stayed on air on RNZ National during last November’s magnitude 7.8 Kaikoura earthquake, calmly reporting the shaking as it got progressively worse.

Did you know? Most Japanese youngsters are trained to recognise an earthquake P-wave if they are on the ground or nearby and react accordingly. An earthquake P-wave is quite distinctive and a trained observer can detect one in some masonry buildings of up to four storeys. With this awareness there will be some false alarms, but it is a handy skill to have. With the move to high-rise tenancy buildings, this skill becomes less effective.

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