In a region prone to earthquakes, a little warning could make a big difference. Though current early warning systemsâsuch as those in Japan, Mexico and Taiwanâcan only give a few to tens of seconds warning before the ground starts to shake, this is enough time to allow some short-term mitigation. Trains and elevators can be slowed or stopped, utilities and factories can put into safe modes, and people indoors and out can move to safer areas. Damage will still occur, but it could be lessened.
Japan is particularly earthquake prone (above, Tokyo devastated after a 1923 earthquake), so itâs no surprise that the country would develop an earthquake early warning system. After years of development, it went online in October. However, the success of the system has been called into question. On January 26, a magnitude 4.8 earthquake shook the Noto Peninsula in the Ishikawa Prefecture about 200 miles northwest of Tokyo. No warning had been issued for the quake, and the Japanese media claimed that system had failed. But did it?
The Japanese system is designed to issue a warning only if the predicted intensity of the earthquake will reach lower 5 or above. (Intensityâsee here for an explanation of the Japanese scaleâis a measure of the strength of seismic motion at the surface, whereas magnitude is a measure of the energy released at the source of an earthquake.) An earthquake with an intensity of 4 will shake books off the shelf; in a lower 5, the bookshelf will fall over. For the January 26 earthquake, the system predicted an intensity of 4, but in one town, Wajimamonzen, the intensity reached lower 5. Government officials from the Ishikawa Prefecture, though, received no reports of injuries or damage from the earthquake. And a representative of the Japan Meteorological Agency told the journal Nature that this kind of variation was within expected limits.
It can be argued that, technically, the system did fail and there should have been a warning. With a system still in its first year of operation, it is no surprise that it still needs perfecting. However, if there was no serious damage from the earthquake, and the system is meant to mitigate damage, doesnât this also call into question where they have placed the cutoff? If warnings are given too often for quakes that donât do much damage, is there a danger people would grow complacent and begin to ignore them? And then what would happen when Japanâs equivalent of the âbig oneâ? (see Tokyo Tremors in Earthquake!) occurs?