Earthquake swarms: The latest hazard of climate change

We tend to think of earthquakes as purely geological events – a result of shifting tectonic plates and churning pressure far beneath our feet. But what if our weather and climate change can also play a role? A new study led by MIT scientists suggests that the heavy rains and snowstorms caused by climate change have the potential to trigger earthquake swarms.

Noto Peninsula and earthquake swarm

The focus of the MIT study was a region in Japan called the Noto Peninsula. This finger-shaped landmass has experienced ongoing earthquake activity for over a decade. The specific type of earthquake activity observed is known as an earthquake swarm, characterized by a series of smaller quakes happening continuously without a clear main event.

The researchers at MIT aimed to unravel the mysteries behind this relentless seismic unrest in the Noto Peninsula. Their investigation on earthquakes went beyond the usual focus on subterranean activity and ventured into the realm of climate change data.

“We see that snowfall and other environmental loading at the surface impacts the stress state underground, and the timing of intense precipitation events is well-correlated with the start of this earthquake swarm,” noted William Frank, an assistant professor at MIT.

More about earthquake swarm

When we think of earthquakes, we usually picture one large shock followed by a series of smaller tremors. This sequence starts with the “mainshock,” the primary and largest earthquake event, and is followed by smaller tremors known as “aftershocks.” These aftershocks can continue for weeks, months, or even years as the Earth’s crust readjusts after the initial rupture.

An earthquake swarm, however, operates differently. Unlike a typical earthquake sequence that features a distinct mainshock, an earthquake swarm lacks a single, identifiable main event. Instead, it’s characterized by a series of smaller, ongoing earthquakes of roughly similar magnitude. The swarm may continue for days, weeks, or even months without a clear focal point.

The key difference between a typical earthquake sequence and an earthquake swarm lies in the absence of a distinct mainshock. In a conventional earthquake sequence, aftershocks generally decrease in magnitude over time.

In an earthquake swarm, the tremors are of similar magnitude and occur without a consistent pattern. While a typical earthquake sequence often follows a predictable decay pattern, a swarm can last for an unpredictable period, sometimes stretching over years.

This phenomenon is precisely what’s shaking up Japan’s Noto Peninsula, a rugged region that juts into the Sea of Japan. Since late 2020, hundreds of small earthquakes have rattled the region in an unusual swarm.

Instead of starting with a mainshock, the Noto Peninsula swarm began with a gradual increase in seismic activity. The earthquakes intensified and clustered, creating persistent tremors unlike the mainshock-aftershock model.

Japan’s history

As mentioned earlier, Japan’s Noto Peninsula is a region accustomed to occasional tremors. This area has a history of seismic activity stretching back over a decade. However, in recent years, this unrest has reached new heights. Since 2020, the peninsula has become a hotbed of small but continuous earthquakes swarms.

The constant shaking has raised concerns and prompted a quest for answers. The team of MIT researchers decided to embark on an in-depth investigation, looking for patterns within the seismic history of the region. They meticulously analyzed earthquake catalogs and records of past tremors, and dove into detailed meteorological data in search of a potential explanation for these relentless quakes.

Climate change and earthquake swarms

By analyzing earthquake frequency in the Noto Peninsula, the researchers pinpointed a distinct seismic change. Prior to 2020, the occurrence of quakes appeared sporadic, displaying no discernible pattern. However, a dramatic shift took place in 2020. Earthquakes began to cluster together tightly in time, signaling the initiation of the ongoing swarm.

But the real surprise came when researchers investigated seismic velocity – the speed at which earthquake-generated waves travel through Earth’s layers. This measurement revealed a remarkable correlation. Changes in seismic velocity seemed to follow a seasonal rhythm, intriguingly aligned with the timing of the earthquake swarm.

This discovery raised a tantalizing question: What environmental factor, caused by climate change, could potentially influence the timing and intensification of earthquakes in the Noto Peninsula?

Snow, climate change, and earthquakes

Heavy snowfall events, as it turns out, are a critical piece of the puzzle. When snow piles up, it adds immense weight to the earth. This weight, combined with rainfall, increases what scientists call “pore fluid pressure.” That’s the pressure fluids exert within the minuscule cracks and gaps in the bedrock beneath us.

Think of it like a sponge. Waterlogged rock, heavy from snow and rain, is more susceptible to the forces deep underground, sometimes causing it to fail and slip – resulting in earthquakes. It’s important to note that this doesn’t replace plate tectonics as the earthquakes’ primary cause, but it can act as the final push.

Climate change implications for earthquake

The big question now is whether this link between climate events and earthquakes is specific to Japan’s Noto Peninsula, or if it has broader global implications. Researchers at MIT believe this connection could extend far beyond this single region. The findings suggest that other locations around the world might also be susceptible to earthquakes influenced by climate.

As the undeniable reality of climate change unfolds, it brings with it an increase in extreme weather events. This includes periods of intense precipitation and snowfall. The MIT study indicates that these intensified weather patterns could potentially exacerbate the effects observed in Japan, leading to more frequent or even stronger earthquakes in vulnerable areas.

The research underscores the complex interplay between various Earth systems – the delicate balance between the atmosphere, the solid ground beneath our feet, and the potential for seismic activity. Further investigations are needed to solidify the connection in climate change and earthquake to pinpoint the specific regions that might be most at risk.

“If we’re going into a climate that’s changing, with more extreme precipitation events…that will change how the Earth’s crust is loaded,” said Professor Frank.

The study is published in the journal Science Advances.

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