Aftershock forecasts

Aftershock forecasts are a tool that scientists use to communicate aftershock risk to the public. These forecasts are time-dependent probabilities of future earthquakes risks and hazards and have been released by scientific organizations in the United States, New Zealand and Japan since the late 1970s.

Thus, it is important that these forecasts are communicated clearly so that citizens can prepare for aftershocks and so that policies are developed to mitigate earthquake hazard and risk.

Check out the following piece from

And let us know : have you ever received an aftershock forecast ? did you find it easy to understand ? Useful ?


SO if I get it well, aftershock forecast are just like weather forecast but for earthquakes?

That’s indeed a nice comparisons, for weather forecast weather services calculate the probabilty for rain, snow etc… and their instruments and knowledge are very advanced so their probabilities are quite precise.

For aftershock forecast seismic institutions also calculate the probability of smaller earthquakes (aftershock)occuring after a big earthquake occured (the mainshock) within a time window of the order of some days or weeks.

Aftershocks are unpredictable.

However,they follow some statistical law:

:point_right: on average there tends to be fewer aftershocks as time goes on. This is Omori’s law

:point_right: a larger earthquake tends to produce more aftershocks than a smaller earthquake. This is Utsu-Seki’s law

:point_right: the magnitude of the largest aftershock is, on average, 1.2 units smaller than the magnitude of the mainshock. This is Bath’s law

Hope this helps! :smiley:


Except that because it’s an aftershock forecast we’re most likely NOT going to die, because it will be smaller than the mainshock…
We still should beware of damaged buildings that may fall if they have been fragilized by the mainshock.

So it’s mostly useful to help us getting ready and decrease our anxiety !

In Japan, after a concern that a 20% chance of M6.0+ aftershock (last page of the PDF) may be perceived as a low probability, the JMA now uses aftershock probability in relative sense.

more information


super interesting ! Is there any survey about whether it’s working better or not?

More info about earthquake forecast: new research found that it’s important to study several faults in order to get more precise forecast => read more : Connecting faults improves earthquake forecasting models -

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