In Japan, an Earthquake Early Warning is a warning issued when an earthquake is detected. The warnings are primarily issued by the Japan Meteorological Agency.

When a P-wave is detected from two (or more) of the 4,235 seismometers installed throughout Japan, the JMA analyzes and predicts the approximate location of the earthquake’s epicentre. This allows the JMA to notify people in affected prefectures by TV and radio if a strong earthquake is expected. An Earthquake Early Warning is issued to warn the general public when an earthquake of 5 or higher on the Japan seismic scale is expected. The system was developed to minimize earthquake damage and enable people to take shelter or evacuate dangerous areas before the arrival of its strong surface waves. It is used by railways to slow trains and by factories to halt assembly lines before the earthquake hits. After receiving a warning, a person has from a few seconds to a minute or more to take action. The effectiveness of the warning depends on the position of the receiver. Areas near an epicenter may experience strong tremors before a warning is issued (Wilkipedia, 2019).