A swarm of small earthquakes began early Tuesday morning beneath Mount Rainier, with more than several hundred minor tremors recorded as of midday, according to scientists with the U.S. Geological Survey and the University of Washington.
The activity began at 1:29 a.m. on July 8 and was detected by the Cascades Volcano Observatory (CVO) and the Pacific Northwest Seismic Network (PNSN).
Researchers said the ongoing swarm is larger than the typical one or two smaller swarms that occur at the volcano each year.
The strongest quake so far reached magnitude 1.7, and most of the events have been located between 1.2 and 3.7 miles (2 to 6 kilometers) below the surface.
A map released by the agencies shows the current swarm in orange, with earlier activity since 2020 in blue.
There have been no signs of ground deformation based on data from GPS monitoring stations around the mountain, according to USGS.
Additionally, there are no visible changes on webcams and no infrasound or other seismic indicators of volcanic unrest.
“Earthquake swarms like this have been attributed to circulation of hydrothermal fluids that are interacting with preexisting faults at shallow levels below the summit of the volcano,” USGS officials said in a notice.
The last time Mount Rainier experienced a swarm of this size was in 2009, when hundreds of earthquakes occurred over a three-day period, with the largest reaching magnitude 2.3.
KIRO 7 asked Harold Tobin, the Director of the Pacific Northwest Seismic Network, how concerned the general public should be.
“At this point in time, I want to be really clear, this is not really cause for concern,” Tobin said.
Tobin reiterated though that scientists are certainly paying attention to it.
“A swarm like this is an unusual event, and we’ll see how things develop over the course of today and coming days,” he said.
USGS emphasized that Mount Rainier remains under close observation by a wide network of seismic, infrasound, GPS, and webcam stations.
Scientists will continue to monitor the activity and issue further updates if necessary.
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