The Earthquake Early Warning System for the General Public

Prospects and Issues for the Prevention and Reduction of Disasters

October 2008

The “Earthquake Early Warning (EEW)” system for the general public is a one-of-its-kind system in the world for disaster prevention information, providing warning via TV and radio before strong tremors arrive. It has been a year since the start of the system in October last year.
When an earthquake occurs, the seismometer catches the initial microtremors (P waves) and predicts the intensity of the coming earthquake from its primary tremor (S waves). The warning system for the general public is announced when intensity of 5 lower or above is expected. There were seven warnings announced by July of this year.

In the Iwate-Miyagi Nairiku Earthquake this June, a strong earthquake with an intensity of ‘6 upper’ (magnitude of 7.2) caused great damage. A warning for the general public was announced 4.5 seconds after the seismometer first caught the P waves. According to the Japan Meteorological Agency, the warning did not reach areas near the epicenter in time, but in some regions of Sendai City, 15 seconds of window time, from the warning to the main tremor, was afforded. NHK’s terrestrial analogue TV broadcast announced the warning one second after the JMA announcement, and the radio broadcast announced 1.3 seconds after.

The Iwate Prefecture Northern Coast Earthquake of July 2008 also caused great damage with an intensity of ‘6 upper,’ but the nature of the quake, with a deep epicenter, is difficult to analyze, and so the warning for the general public took 20.8 seconds, and was not announced in time for most of Iwate.

The private research company Survey Research Center conducted a survey to 683 adults in Sendai, Morioka and Fukushima after the Iwate-Miyagi Nairiku Earthquake and close to 40 percent answered that they heard/saw the warning, but there were differences as to when they noticed it, which means one out of every four person heard/saw the report after the tremor. Also, many people mistook the warning as a flash report for an earthquake that had already occurred.

The challenge is to announce the warning in a way that is ‘quick, accurate and easy to understand.’ The JMA must catch the P waves as soon as possible and provide accurate analyses, and to this end, the JMA has started placing EEW-compliant ocean-bottom seismographs. Broadcasters must also work to announce the warnings faster. Digital will take more time compared to analogue, but NHK is currently researching a system to provide quick warnings to ‘One-Seg’ cell phones.

The NHK Monthly Report on Broadcast Research