A magnitude 7.0 earthquake Saturday morning spawned a series of aftershocks that rattled communities throughout Southeast Alaska and Yukon.
Dozens of people from Valdez to Whitehorse to Southeast Alaska reported to the United States Geological Survey that they’d felt the earthquake, which occurred about 11:40 a.m. according to Alaska Earthquake Center data.
The epicenter was first measured in an area about 55 miles north of Yakutat. Emergency personnel had not heard any reports of damage or injuries.
“A good, long, rolling shaker for sure,” Yakutat fire chief Casey Mapes said. “My daughter in Anchorage said she felt it.”
When an earthquake like this happens, battalion chief Max Mielke said they worry most about the potential of a landslide somewhere in Yakutat Bay or nearby Russell Fjord.
Earthquake center director Mike West said he flagged that same concern for state emergency operations personnel when they called him Saturday afternoon.
“Magnitude 7 is large enough to shake loose landslides historically,” he said. But he has heard no reports of landslides.
Yakutat’s unique geography
West said he expects this cluster of earthquakes and aftershocks will generate a lot of interest from scientists because the region is so geologically complex.
“It’s a geologic trainwreck,” he said.
The region includes the Yakutat microplate, which sits at what West called the “corner” of Alaska where the Pacific and North American tectonic plates converge.
On the Pacific plate side, West said one could think of the Aleutian Islands.
“Out in the Aleutians, you have these large earthquakes, but a really well understood process. It’s a subduction zone,” he said.
That’s an area where two tectonic plates collide and one dives beneath the other.
“And, sure, we can split hairs about exactly what the behavior is – but we understand what a subduction zone is,” he said.
On the Pacific plate side, one can look at southeast Alaska, near Sitka, where a massive strike-slip fault system runs along the coast. That’s a type of fault where plates slide past each other.
“It’s like our northern version of the San Andreas fault,” West said, referring to one of the more famous faults in the world located in California where an earthquake in San Francisco in 1906 is responsible for the deaths of at least 3,000 people.
“The Yakutat region is the intersection of these two – thousand mile scale geologic processes and, honestly, that whole region down around Yakutat and Prince William Sound is kind of a geologic train wreck,” West said.
In the coming days, scientists will try to pin down on which faultline the earthquake centered
Though it would be a mistake to assume it happened in one small spot, West said.
“A magnitude 7 earthquake — this thing should be many miles long,” he said. “This is not a point on a map.”
Area residents posted on social media they felt a rolling or swaying motion. West said that’s generally a good indicator of the size of the earthquake.
“Those rolling waves are a sign of a big earthquake,” he said. “Those big rolling waves don’t happen in our run-of-the-mill magnitude 5 [earthquakes] where you feel a little bang, and then it’s kind of over,” he said. “Roughly speaking, a magnitude 5 earthquake – the actual rupture itself is over in a couple of seconds. In a magnitude 7, we’re talking about something that probably took tens of seconds to actually complete.”
The earthquake center is calling it the Hubbard Glacier earthquake and reports that more than 20 aftershocks of magnitude 3 or higher have followed the initial main shock, with the largest ranging from magnitude 4 up to 5.1.
This is a breaking news story that will be updated