from the desk of Senior Editor Jean Kumagai:
Since last month's deadly earthquake in Japan, I've been wondering how the country's automated earthquake early-warning network performed during the magnitude 6.8 event. The early-warning network consists of more than 1000 seismic stations scattered around Japan and is designed to detect the first tremors of an earthquake, calculate the likely source and magnitude, and then broadcast an alert, all within seconds. Depending on how far you are from the epicenter, the alert may give you a brief window''at most tens of seconds''to take cover before the full force of the earthquake strikes. The further you are from the epicenter, the longer your lead time.
Yesterday Osamu Kamigaichi of the Japan Meteorological Agency (JMA) emailed me a brief report on how the EEW system performed. The alerts appeared to go to the appropriate recipients, who in most cases took appropriate action, Kamigaichi wrote. For example, at a construction site in Matsumoto-city, about 170 km from the quake's epicenter, workers responded to the alert by stopping a moving crane. And in Tachikawa-city, near Tokyo, the elevators at a hospital automatically went to the next floor, opened their doors, and informed passengers of the impending temblor.
So why didn't the alerts prevent more casualties and destruction? For one thing, Kamigaichi pointed out, the alerts are at present being distributed to only a limited set of users, including some schools, railroads, and communications companies. Starting this October, though, JMA plans to start broadcasting the alerts to the general public. In the mean time, the government has been trying to educate people so that they don''t panic when they hear an alert. The educational campaign still has a ways to go, judging by reactions in Ueda-city, in Nagano prefecture. There, Kamigaichi wrote, the earthquake warning was broadcast to the local community, and some people didn't know how to respond or ignored the alert altogether.
For those closest to the epicenter, the alerts don''t provide enough time to react. That was the case at the Kashiwazaki Kariwa nuclear power plant, which suffered extensive damage and remains closed. All nuclear power plants in Japan are equipped with their own seismometers, however, and in this case the reactors did shut down automatically.
Early-warning alerts also won''t prevent buildings from collapsing, which accounted for many of the casualties in the 16 July earthquake. You still need stringent building codes and zoning rules. And you probably shouldn''t construct nuclear reactors on top of active faults.