Japan Trench is locking up again, scientists warn, as in the run-up to 2011

The fault that unleashed one of the worst earthquakes in modern history is building up strain again. Scientists say it now looks much like it did before 2011.

Researchers at Tohoku University in Japan report that the Japan Trench, which ruptured in 2011, has locked once more. Their study was published in the journal Science.

What did the researchers find?

Seafloor measurements show that the slow slip left over from the 2011 quake had largely stopped by 2021. In other words, the plates are no longer creeping past each other. They are stuck.

According to the team, that locked state resembles the condition of the fault before the 2011 disaster. When a fault locks, energy keeps accumulating until it is eventually released.

The researchers warn that the next major earthquake could arrive much earlier than the averages over hundreds of years would suggest. The study does not give a date.

What happened in 2011?

On 11 March 2011, a magnitude 9.0 earthquake struck along the Japan Trench. The tsunami it triggered devastated Japan's northeast coast and caused the Fukushima nuclear disaster.

The waves also crossed the Pacific. In the United States, the tsunami caused about 100 million dollars in damage at dozens of ports. Crescent City, in California, was hit hardest.

Even at low tide, the wave there reached roughly 2.4 metres. One person died.

Why does it matter now?

The 2011 disaster was not only a Japanese tragedy. Its effects reached far across the ocean, which is why a fault re-locking is being watched well beyond Japan.

For now, this is a scientific warning about a pattern, not a prediction of a specific quake. What the data show is that the energy is building again, and that the usual long-term averages may not be a reliable guide to when the fault will next give way.