A years-long swarm of thousands of earthquakes in Japan was probably triggered by heavy snow and other environmental factors such as rain and rising sea levels.
鈥淭he changing climate can have some impact on the stress state of the Earth beneath our feet,鈥� says at the Massachusetts Institute of Technology. But the role human-caused climate change played in these quakes remains uncertain, she says.
The shaking began in Japan鈥檚 Noto peninsula on the island of Honshu near the end of 2020. Since then, the area has experienced more than 100 small earthquakes per day. On the first day of 2024, the region felt a large magnitude-7.5 earthquake that destroyed tens of thousands of buildings and killed at least 240 people. But it is unclear whether that quake fits within the swarm.
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Wang and her colleagues analysed a record of seismic activity in the region between 2012 and 2023 to investigate what triggered the swarm, which ranks among the largest ever observed. These swarms commonly erupt in volcanic regions, but typically last just weeks or months.
The researchers suspected these partly stem from a rise in the pressure of fluid within porous rocks located kilometres underground. With such excess pressure, 鈥渢he whole structure becomes weak鈥�, says Wang.
Fluctuating weight on the surface from sources like rain, snow, atmospheric pressure and sea level can also shift pore pressure, somewhat like stepping on wet sand, she says. When combined with high pressure from fluid below, it could trigger earthquake swarms.
The team modelled the influence of upwelling fluids and variations in surface weight on pore pressure.
Snowfall seemed to have the greatest influence of all surface factors. When the researchers included snow鈥檚 influence on pore pressure in the model, the correlation with seismic measurements improved by 10 per cent compared with a model without snow. A clear seasonal pattern in the seismic activity also supported a link between the swarm and changes in weather.
This does not suggest that snow or other environmental factors solely caused the earthquake swarm, says Wang. But she thinks they put more pressure on fractures and faults already weakened by excess pore pressure.
鈥淭hese guys made a pretty good case that water is the culprit,鈥� says at the University of South Florida. But this doesn鈥檛 necessarily mean snowfall often triggers earthquakes elsewhere, he says. 鈥淚s this a one-off [situation]? Or is this a general phenomenon?鈥�
Snowfall or other changes in water load has been linked to 鈥渕odest changes in seismicity鈥� elsewhere in Japan, as well as the Himalaya mountains, California, East Africa and Taiwan, says at the University of California, Berkeley. However, he says it is nearly impossible to conclude whether they impacted any individual earthquake.
Researchers are also still working out how environmental drivers of earthquakes could be linked to anthropogenic climate change, says McNutt. Climate-related changes like melting glaciers and ice sheets, rising sea level and 鈥� as in Noto 鈥� heavy precipitation are all possible contributors to earthquakes.
While climate change will probably have some effect on seismic activity, B眉rgmann says 鈥渃hanges in earthquake hazard should probably be the least of our concerns when it comes to the impact of climate change鈥�.
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