EEW (Earthquake Early Warning)


日本語版 (Japanese)


What is an EEW?

Source: JMA website

EEW is a system that predicts the arrival time and shaking of earthquakes immediately after they occur, and provides this information quickly through various media (TV, radio, etc.).
Specifically, when an earthquake occurs, seismic waves are generated from the epicenter, and seismographs near the epicenter observe Primary waves (vertical shaking). Based on this, the magnitude of the Secondary wave (large horizontal tremor) is predicted and quickly provided through various media.
EEW is forecasted in increments of 0.1 to several seconds, so there may be some errors.
However, this has the disadvantage that it takes several seconds from the detection of the Primary wave to the delivery of the preliminary report, so the preliminary report often does not arrive in time if it is close to the epicenter.

There are two types of EEW “Forecast” and “Warning” Among warning, when seismic intensity 6-lower or greater are expected, they are positioned as “Special Warning” but Special Warnings are issued without distinction from warnings.

More information is available on the JMA website.


EEW Forecast

EEW (Forecast) is issued when the following conditions are met.

  • When the amplitude of the Primary or Secondary wave is 100 gals or more at any of the seismic stations
  • When the seismic waves observed by seismographs are analyzed to obtain the epicenter, magnitude, and predicted seismic intensity for each region, and the magnitude is 3.5 or greater, or the maximum predicted seismic intensity is 3 or greater.

*Quotes from the JMA website

In addition to being used for device control, it is also used for advanced users, such as displaying the expected seismic intensity at the receiving point and the expected arrival time of Secondary wave on home terminals.


EEW Warning

EEW, which is often broadcast on TV and radio, is played when there is a warning. EEW (Warning) is played when the following conditions are met.

  • When seismic waves are observed at two or more seismic stations and the maximum intensity is expected to be 5-lower or more.
  • When long-period seismic motion class 3 or more is expected

*Quotes from the JMA website

When an EEW (Warning) is issued, the seismic intensity of 4 or more is announced as the target area after taking into account the margin of error.


PLUM (Propagation of Local Undamped Motion) method

EEW may be issued as a follow-up report. Specifically, the PLUM method does not estimate the epicenter or scale of the earthquake, but directly predicts the seismic intensity based on the strength of the shaking observed by seismographs.
The PLUM method is presented in the following cases.

  • A follow-up earthquake alert is issued when a new seismic intensity of 5-lower or more or long-period seismic motion class 3 or more is expected in an area where no warning has been issued based on analysis after an EEW is issued.
  • In the follow-up report, we will announce new areas where seismic intensity of 5-lower or long-period seismic motion class 3 or more is expected and new areas where seismic intensity of 4 is expected.
  • Only EEW (false alarms) that are sent out due to misidentification of phenomena other than earthquakes, such as lightning strikes, as earthquakes will be cancelled, and not, for example, when an earthquake intensity of 3 or lower is predicted for an area where an intensity of 5-lower is predicted.

*Quotes from the JMA website


How to respond

When you receive a breaking news, protect yourself first.
If you receive the breaking news indoors, immediately open windows and doors to clear an evacuation route, move away from falling or falling objects, and hide under a desk or table to protect your head. In addition, many homes are considered safe zones, especially in hallways. Therefore, it is also recommended that you evacuate to the hallway first when you hear the sound of an earthquake early warning or notice the tremors of an earthquake.
However, if you are sound asleep and notice the sound of an EEW or the shaking of an earthquake, do not act forcibly, but instead wrap yourself up in your futon and protect yourself with a pillow or something similar.

In crowded areas, protect your head and stay away from falling objects, signs, lights, and other falling objects. Do not crowd the exits and follow the instructions of the attendant when asked.

If you receive a preliminary report outdoors, evacuate to a quake-resistant building away from block walls and other falling objects, as well as signboards, lights, window glass, and other falling objects.

If you are driving a motor vehicle, turn on your hazard lights, slow down, and move to the left side of the road to stop. Avoid sharp steering and sudden stops. If you are on a bus or train, support yourself by holding onto the strap or handrail. If you are in an elevator, press all floor buttons so that the elevator will stop at the nearest floor.