Not all the noise in Sitka on New Year’s Day was fireworks. An earthquake rattled doors and windows of many homes in the community on the evening of January 1. And although the magnitude 3 temblor was small, it was close by, underneath Sitka’s iconic — and dormant — Mt. Edgecumbe volcano.
The epicenter for the earthquake on January 1 was only 16 miles from town, about two miles deep, under Kruzof Island. But Ken Macpherson, the on-call seismologist with the Alaska Earthquake Center at UAF who recorded the quake, says that doesn’t mean the centuries-long dormant volcano, Mt. Edgecumbe, will be smoking any time soon.
“We do see lots of volcanic events, particularly in the Aleutians and in the Katmai area,” says Macpherson. “This earthquake wasn’t associated with a volcano, just a traditional or conventional tectonic earthquake.”
Tectonic earthquakes are pretty regular near Sitka. To the west is the Queen Charlotte-Fairweather Fault System, which sees a lot of low rumblings. But Macpherson says while these small quakes are really common, there was one unusual thing about this one.
“It’s interesting because it was so shallow and so close to Sitka, usually when we see a magnitude 3 in Alaska, we don’t assume that anyone’s going to feel it,” he says.
But some people did feel it. Social media in Sitka lit up in the minutes following the quake, with people wondering what had just happened. A thread started with information from the US Geological Survey about a magnitude 4.7 earthquake near Monterey, California, which happened about the same time — but that event was unrelated to the Sitka quake. The US Tsunami Warning System doesn’t publish information about earthquakes less than magnitude 4. There are just too many.
Macpherson says that there’s a general rule of thumb: With every step down in magnitude, the amount of earthquakes increases tenfold.
“On the globe, there’s maybe one magnitude 8 every year. But if you go down to magnitude 7, you get ten times that many, or 100 magnitude 6’s,” he says. “When you get down to magnitude 3 or 2, we’re getting hundreds of earthquakes like that,” globally, and he says dozens in Alaska every day.
There were 41 earthquakes in Alaska, in the 24 hours before Sitka’s 3.0 earthquake at 10:02 p.m. on New Year’s Day. And many more in the hours afterward. Only three exceeded a magnitude 4.
The center tracks earthquakes in real time and posts the data for the public within minutes. Each earthquake on their interactive map is represented by a tiny red or yellow dot. Looking at a map of seismic activity over the last month, the state looks like it has a bad case of the chicken pox.
Still, it’s rare for a magnitude 3 quake to get so many people talking. And the seismologists would like to know more. Macpherson asks that people report noticeable quakes to the US Geological Survey’s “Did you feel it?” page.
“There, you can report on what you experienced, what you felt, what the level of shaking was,” he says. “That data is very, very useful for scientists because it can be used to learn something about how the waves propagate, and that has implications for seismic hazard.”
And he says to rely on Alaska Earthquake Center’s website or Facebook page, rather than third party apps that may not provide reliable information.
Editors Note: An earlier version of this story quoted Ken Macpherson saying there are hundreds of magnitude 3 and lower earthquakes happening daily in Alaska. After publication, Macpherson clarified that there are hundreds of small earthquakes happening daily on a global scale, but only dozens per day in Alaska. The above text has been amended to clarify that difference.
