Frostquakes are seismic events with frequencies of about 10-20 Hz and waveforms like those of tectonic events. They potentially can damage infrastructures and have to be taken into account in seismic hazard assessment.
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Winter in Finland. Image credit: Andreas.
Frostquakes have attracted public attention recently, as multiple reports about them from local inhabitants in Arctic and sub-Arctic areas appeared in social networks.
“When occurred in populated areas, these events are felt by people and they can be accompanied by specific noises,” said University of Oulu’s Professor Elena Kozlovskaya and her colleagues.
“Ground motions during frostquakes are comparable to those of other seismic events, such as more distant earthquakes, mining explosions and vibrations produced by freight trains.”
To make an instrumental study of such events, the researchers installed two high-resolution seismic arrays with co-located soil temperature stations at two sites in Finland: one of them being in the city of Oulu in the sub-Arctic area and the other one, above the Polar Circle in municipality of Sodankylä.
During several days when the air temperature was decreasing rapidly, the local residents reported ground tremors and unusual sounds to the team. These observations were used to identify frostquakes from seismic data.
The conditions for a frostquake are favorable when the temperature drops to more than minus 20 degrees Celsius at a rate of about one degree per hour.
The scientists also found that fracturing in the uppermost frozen ground can be initiated if the thickness of frozen layer is about 5 cm and larger.
Ruptures can propagate deeper and damage infrastructure such as buildings, basements, pipelines and roads.
“With climate change, rapid changes in weather patterns have brought frostquakes to the attention of the wider audience, and they may become more common,” said Dr. Kari Moisio, a researcher at the University of Oulu.
“Although their intensity is usually low, a series of relatively strong frostquakes in Oulu, 2016, which ruptured roads, was the starting point for our research.”
“Frostquakes affect northern regions internationally, but they have been little studied using seismic instrumentation.”
“Frostquakes have often occurred in January, but other times are also possible.”
“During frostquakes, seismic surface waves produce high ground accelerations at distances of up to hundreds of meters.”
“The fractures during frostquakes seem to propagate along drainage channels near roads and in irrigated wetlands,” Professor Kozlovskaya said.
The findings were published in the journal EGUsphere.
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Nikita Afonin et al. Frost quakes in wetlands in northern Finland during extreme winter weather conditions and related hazard to urban infrastructure. EGUsphere, published online September 14, 2023; doi: 10.5194/egusphere-2023-1853
