Scientists have found that, in addition to looking for the causes of earthquakes in the collision of tectonic plates or the movement of faults, attention must also be paid to the climate as a "second-order factor".

This pioneering investigation has already monitored some earthquakes that have occurred in recent years -- in addition to other current tremors -- in Japan, which may have been conditioned by previous meteorological phenomena.

"We see that snowfall and other shallow environmental loads influence the state of stress in the subsurface, and the timing of the heavy rainfall is very closely related," said William Frank, co-author of the study and an associate professor in MIT's Department of Earth, Atmospheric and Planetary Sciences (EAPS).

The project also included former MIT postdoc Qing-Yu Wang, now at the University of Grenoble Alpes, EAPS postdoc Xin Cui, Yang Lu of the University of Vienna, Takashi Hirose of Tohoku University, and Kazushige Obara of the University of Tokyo.

The MIT team, together with Japanese partners, has been trying to detect patterns that explain the persistence of earthquakes in the Noto Peninsula (Japan) since the end of 2020, where, according to the study, multiple continuous earthquakes occurred without a clear initial shock or trigger, as is usual.

The researchers consulted the earthquake record of the Japan Meteorological Agency, and monitoring points throughout the country, over the past 11 years, to get an idea of the speed at which a seismic wave traveled between these stations.

Thus, the researchers generated an evolving image of the seismic velocity beneath the Noto Peninsula and observed that, since 2020, changes in wave velocity appeared to be synchronized with the seasons.

"When it rains or snows, it adds weight, which increases the pressure, which allows seismic waves to travel more slowly, and when all that weight is removed, through evaporation or runoff, suddenly the pressure drops and the seismic waves are faster," Frank said.

In this way, the scientists found that the succession of earthquakes suffered by the inhabitants of Noto can be explained in part by the seasonal rains and, in particular, by the heavy snowfalls.

"We see that the timing of the earthquakes coincides perfectly with the timing of the heavy snowfalls," Frank said, although he emphasizes that these are "second-order factors" and that the main 'trigger' will always originate in the subsoil.

The researchers now suspect that this new link between earthquakes and climate may not be unique to Japan and may play a role in seismic activity in other parts of the world.

In addition, they predict that the influence of climate on earthquakes could be more pronounced with global warming because the world is in a "changing climate with more extreme precipitation".

This will modify "the way weight acts on the Earth's crust" and will certainly have an impact on earthquakes, they warned.

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