Study: Snowfall and heavy rain may contribute to the occurrence of some earthquakes MIT News

When scientists search for the cause of an earthquake, their search often begins underground. As centuries of seismic studies have shown, it is the collision of tectonic plates and the movement of faults and fissures beneath the surface that primarily causes an earthquake.

But MIT scientists have now found that certain weather events may also play a role in causing some earthquakes.

In a study appearing today in Science Advances, researchers report that episodes of heavy snowfall and rain likely contributed to a cluster of earthquakes over the past few years in northern Japan. This study is the first to show that climatic conditions can lead to some earthquakes.

“We see that snowfall and other environmental loading at the surface affects the stress state underground, and the timing of extreme precipitation events correlates well with the onset of an earthquake swarm,” says study author William Frank, an assistant professor in the MIT department. Earth, Atmospheric and Planetary Sciences (EAPS). “So, climate clearly has an impact on the response of solid Earth, and part of that response is earthquakes.”

The new study focuses on an ongoing series of earthquakes on Japan's Noto Peninsula. The team discovered that seismic activity in the region coincides surprisingly closely with certain changes in underground pressure, and that those changes are affected by seasonal patterns of snowfall and precipitation. Scientists believe that this new link between earthquakes and climate may not be limited to Japan, and could play a role in shaking other parts of the world.

Looking to the future, they expect that climate's impact on earthquakes could be more pronounced with global warming.

“If we are heading towards a changing climate, with more extreme rainfall, and we expect water to be redistributed in the atmosphere, oceans and continents, that will change how the Earth's crust is loaded,” Frank adds. “That will definitely have an impact, and it's a link we can explore further.”

The study's lead author is Qingyu Wang, a former research associate at MIT (now at the University of Grenoble Alpes), and also includes Shen Cui, a postdoctoral researcher at EAPS, Yang Lu of the University of Vienna, Takashi Hirose of Tohoku University, and Kazushige Obara of University of Vienna. Tokyo.

Seismic velocity

Since late 2020, hundreds of small earthquakes have rocked Japan's Noto Peninsula — a finger of land that curves north from the country's main island into the Sea of ​​Japan. Unlike a typical earthquake sequence, which begins as a mainshock that gives way to a series of aftershocks before fading away, seismic activity at Noto is a “seismic swarm” — a pattern of multiple, persistent earthquakes without an obvious mainshock or seismic trigger.

The MIT team, along with colleagues in Japan, aimed to discover any patterns in the swarm that would explain the ongoing earthquakes. They began by searching the Japan Meteorological Agency's earthquake catalog, which provides data on seismic activity across the country over time. They focused on earthquakes on the Noto Peninsula over the past 11 years, during which the region has experienced occasional seismic activity, including the recent swarm.

Using seismic data from the catalog, the team counted the number of seismic events that occurred in the region over time, and found that the timing of earthquakes before 2020 appeared sporadic and irrelevant, compared to late 2020, when the quakes became more intense and clustered. In time, marking the beginning of the swarm, with earthquakes that are somehow connected.

The scientists then looked at a second dataset of seismic measurements taken by monitoring stations during the same 11-year period. Each station continuously records any local displacement or vibration that occurs. Vibrating from one station to another can give scientists an idea of ​​how quickly a seismic wave travels between stations. This “seismic velocity” is related to the structure of the Earth through which the seismic wave travels. Wang used station measurements to calculate seismic velocity between every station in and around Noto over the past 11 years.

Researchers created a sophisticated picture of seismic velocity beneath the Noto Peninsula, and noticed a surprising pattern: In 2020, around the time the earthquake swarm is thought to have begun, changes in seismic velocity appeared to synchronize with the seasons.

“We then had to explain why we were observing this seasonal variation,” says Frank.

Snow pressure

The team wondered whether environmental changes from season to season could affect the Earth's infrastructure in a way that would trigger a swarm of earthquakes. Specifically, they looked at how seasonal rainfall affects underground “pore fluid pressure,” which is the amount of pressure that fluids in the ground’s cracks and crevices exert within the rock.

“When it rains or snows, it adds weight, which increases pore pressure, allowing seismic waves to travel through them more slowly,” Frank explains. “When all that weight is removed, through evaporation or runoff, suddenly, the pore pressure drops and the seismic waves become faster.”

Wang and Cui developed a hydromechanical model for the Noto Peninsula to simulate basic pore pressure over the past 11 years in response to seasonal changes in precipitation. They fed model meteorological data from the same period, including daily snow measurements, precipitation and sea level changes. Through their model, they were able to track changes in excess pore pressure under the Noto Peninsula, before and during the earthquake swarm. They then compared this timeline of pore pressure evolution with their evolving picture of seismic velocity.

“We had seismic velocity observations, we had the excess pore pressure model, and when we nested them, we saw that they fit very well,” Frank says.

In particular, they found that when they included snowfall data, especially extreme snowfall events, the fit between the model and observations was stronger than if they took into account only rainfall and other events. In other words, the constant swarm of earthquakes experienced by Noto residents can be partly explained by seasonal rainfall, especially heavy snowfall events.

“We can see that the timing of these earthquakes corresponds very well with multiple times when we have had heavy snowfall,” Frank says. “It correlates well with earthquake activity. We believe there is a physical link between the two.”

Researchers suspect that heavy snowfall and similar heavy rainfall could play a role in earthquakes elsewhere, although they stress that the main cause will always originate underground.

“When we first want to understand how earthquakes work, we look at plate tectonics, because that is the number one reason why earthquakes happen and always will,” says Frank. “But, what other things can affect when and how an earthquake occurs? That's when you start moving to second-order controlling factors, and climate is clearly one of those factors.”

This research was supported in part by the National Science Foundation.

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