Study reveals big storms create “stormquakes”
Location: Washington, United States
Date Published: October 17, 2019
Scientists have discovered a mash-up of two feared disasters — hurricanes and earthquakes — and they’re calling them “stormquakes.”
These events, described this week in Geophysical Research Letters, are pulses of seismic waves birthed from the ferocious energy in massive storms, and they can radiate thousands of miles across continents.
“I was surprised by what they saw,” says Göran Ekström, a seismologist at Columbia University who specializes in unusual earthquakes. Big storms are thought to produce a lengthy jumble of rumbles that radiate from coastlines. But in the new study, the team identified a discrete “burst of wiggles” from each stormquake that they can trace back to its origin offshore.
The find joins a number of recent studies that are applying new methods to sort through the noise recorded on the world’s growing network of seismometers. These signals can help scientists better understand the world around us, from deciphering our planet’s inner structure to tracking ocean or ice dynamics and even monitoring climate change. (Read about how a groundbreaking earthquake catalog may have solved a seismic mystery.)
A lot of this information has previously been discarded as noise in our seismic readings, but scientists are now seeing how that “noise” may be providing useful records of environmental happenings, says study leader Wenyuan Fan, a seismologist at Florida State University.
“We just didn’t know where to look and what to look for,” he says.
Similar to many scientific advances, stormquakes were discovered by accident. In summer 2018, Fan and his colleagues were developing a method to study what are known as very-low-frequency earthquakes. These are not the sudden, intense jolts we usually think of when a temblor unzips our planet’s surface. Instead, these tremors shake the surface in a low-frequency side-to-side warble at intensities below what humans can detect without instrumentation. Geologists can identify these events by the seismic waves they generate, picked up on sensitive instruments known as seismometers.
“Seismometers are basically like little ears pressed to the ground,” explains Wendy Bohon, an earthquake geologist at the Incorporated Research Institutions for Seismology who was not part of the study team. The devices can pick up all sorts of vibrations, from boisterous sports fans jumping up and down and airplanes passing overhead to distant earthquakes rattling the ground.
Very low-frequency earthquakes, however, are tough to trace over vast distances, since the wiggles from these events don’t always look the same from one seismometer to the next, Fan says. So he and his team devised a method to track them, piecing together the signals from smaller regions like a seismic puzzle. But during this process, an unusual set of events emerged that looked similar to, but not exactly like, the earthquakes Fan was chasing.
Surprisingly, the events were seasonal, never occurring between May and August. Earthquakes that release energy from Earth’s shifting crust, however, are usually indifferent to the changing seasons. What’s more, the curious quakes radiated from both the east and west coasts of North America. Earthquakes are common out west, rumbling as the earth shifts along with a spidery network of fractures in the surface, but the eastern coast largely lacks these quake-generating features.
Baffled, Fan and his team turned to models to figure out what was going on—and that was when they realized the connection: Many of these tremors coincided with massive storms or even full-fledged hurricanes. By digging through data largely from EarthScope’s USArray, a series of hundreds of seismometers temporarily placed across the country, the team unearthed 14,077 of these stormquake events between 2006 and 2015.