As rain and snow events become more intense, so could our earthquakes, study finds

A patch of heavy rain might force you to change your plans for a few days. But for the residents of a few Japanese districts, torrential showers have begun to shake up a little more than their daily itineraries, a new bit of shocking research has shown.

A groundbreaking study has found that certain weather phenomena — particularly heavy snowfall and rain — might have been secretly inducing a flurry of earthquakes in some parts of northern Japan in the past few years. This is the first time scientists have found that our weather can have a noticeable effect on seismic activity.

These quakes occurred in Japan's Noto Peninsula, where a series of ongoing seismic events have rattled communities since late 2020. Earthquakes typically start off as a localised main shock — typically the effect of tectonic activity — followed by some aftershocks. However, Noto’s quakes were spread all around, meaning that it didn’t seem like there was a main trigger to them.

Surprisingly enough, the researchers found that these quakes often coincided with heavy precipitation events, particularly when there was intense snowfall activity. This prompted the authors to look into a potential link between the two phenomena.

To get to the bottom of this mystery, the scientists simulated how seasonal precipitation alters pore fluid pressure within the Earth's bedrock. Pore pressure refers to pressure exerted by groundwater when it is trapped within the tiny pores in rock or soil.

"When it rains or snows, that adds weight, which increases pore pressure, which allows seismic waves to travel through slower," study author William Frank explains. "When all that weight is removed, through evaporation or runoff, all of a sudden, that pore pressure decreases and seismic waves are faster."

They found that pore pressure within these Nota Peninsular rocks were being supercharged at some seasonal point, usually during extreme snowfall events. These moments of excess pressure often coincided with the earthquake swarms, meaning that they could be contributing to the tremors.

"When we first want to understand how earthquakes work, we look to plate tectonics, because that is and will always be the number one reason why an earthquake happens," Frank says. "But, what are the other things that could affect when and how an earthquake happens? That's when you start to go to second-order controlling factors, and the climate is obviously one of those."

As Earth's climate evolves, with projections of more extreme weather events due to global warming, understanding the nuances of this climate-earthquake nexus becomes increasingly crucial.

The findings of this research have been published in Science Advances and can be accessed here.