How Japan Perfectly Predicted an Earthquake: “Slow Slip”

In the early hours of the morning (12th of June), Chiba prefecture was hit by a magnitude 4.9 (Shindo 3) earthquake. While this level of earthquake is not rare, the interesting thing is how Japan’s earthquake committee warned that an earthquake was imminent in that exact area the day before it occurred.  


“They predicted it!” – Twitter goes wild

At around 5 am in the morning, a magnitude 3 earthquake hit off the coast from Chiba prefecture. Soon after, Twitter users started tweeting about the prediction.

“It was an earthquake prediction.”

“It’s the first time I’ve known when an earthquake is going to come.” 

These tweets came flooding in when the earthquake committee predicted a larger than usual earthquake just off the coast of Chiba the very day before it occurred.


What is a “Slow Slip”?

How was an earthquake predicted a whole day before it occurred? The key to this is known as a ‘slow slip’. Japan’s ocean tectonic plate slowly slid below the plate above it where the majority of Japan is located – this phenomenon is known as the “slow slip”.

Because the movement causes no major quakes as the plates slowly move, it has become known as a “slow earthquake”. This month, there has been a large number of tiny earthquakes in Chiba that can’t be felt under normal circumstances.

Thanks to GPS, a movement of 1 cm between the two plates were noticed. This lead to the earthquake committee judging that this was, in fact, a “slow slip”.

These slow slips are recorded every few years in Chiba prefecture and almost always, a relatively large earthquake follows. It was these previous earthquakes that have allowed scientists to study the patterns to help earthquake prediction. 

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The truth behind the prediction

While many netizens claim the earthquake was predicted, the chairman of the earthquake committee stated that this was in no way a true prediction of an earthquake. It was simply the fact that within the last 60 years, 7 such “slow slips” have occurred, where a larger than usual earthquake follows between a few days to a week later. Therefore, the committee decided upon warning of a high possibility that an earthquake would hit Chiba.



Can animals predict earthquakes?

The incident sparked interest in netizens about whether animals can sense if an earthquake is near or not.

“When there are no mosquitos, does that mean an earthquake could come”?

“Do bears coming down from the mountain have anything to do with earthquakes?”

However, the chairman of the committee stated that “the behavior and movements of animals and insects depend largely on the climate, weather, and other various factors – so it is difficult to scientifically say if there is any truth in it.”


The 2011 major Tohoku earthquake showed signs of a “slow slip”?

It is not only in Chiba such earthquakes occur. The Tohoku earthquake that occurred 7 years ago that caused a tsunami that killed thousands also showed signs of a slow slip. It was reported that around 1 month before the earthquake occurred, there was a point where a “slow slip” occurred.

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What does this mean for the future of predicting earthquakes?

Unfortunately, just because a “slow slip” occurs, there will not necessarily be a large earthquake afterward. Furthermore, even in cases where a “slow slip” occurs, we do not always have the equipment to be able to detect them. While earthquake prediction is a difficult feat the human race has not yet accomplished – research as the “slow slip” could get us closer to that goal. Perhaps sometime soon, the amount of earthquake “predictions” will vastly increase.