How to Prepare for a Strong Shaking: Earthquake Early Warning in Japan

In Japan, earthquake early warnings have been provided to the public since 2007. The system sends out alerts via cell phone, TV, radio, and other media, with a lead time of a few seconds to tens of seconds before the arrival of strong shaking. It has provided more than 10 warnings of strong earthquakes before the 2011 Tohoku earthquake.

              In March 2011, a major earthquake occurred off the Pacific coast of Tohoku region. The warning system detected the earthquake and, about 8 seconds after the first primary wave arrived at the closest seismic station, issued a warning to the public in the region close to the epicenter. Twenty seven bullet trains were stopped without derailments in this region. Three minutes later, warnings for very large tsunamis were issued to Iwate, Miyagi and Fukushima prefectures. The damaging waves arrived 15–20 minutes later at the closest shores.

The warning was provided for the mainshock, however, there were problems of the system recognized after the earthquake. The percentage of false alarms increased double after the Tohoku earthquake, because of the complication of simultaneously occurring earthquakes. The unexpected character of the seismic data for mega quake fooled the early warning system's algorithms.

              Ever since, substantial efforts were made for the technical improvements of earthquake early warning system. Scientists proposed a new algorithm of the system to reduce the false alarms. More and more practical applications were explored, such as control of elevators, trains, automated systems, etc. The earthquake early warning system in Japan should become a truly effective mitigation tool in a society that has already accepted and learned to expect such information.