On Monday afternoon, Pat Philpott sat in his home near Mile 7 of the Haines Highway, looking out over the glass-calm water of the Chilkat River. 

Then he noticed something strange. 

“I saw ripples,” he said. Short waves, three sets of them, coming toward him from the direction of Kicking Horse River across the inlet – traveling perpendicular/sideways to the normal river flow.  

“I said, ‘what the hell?’ I thought there were animals, but there were no animals,” he said. 

Then, a boom, and his house started rattling. 

The Alaska Earthquake Center reported a magnitude 3 earthquake about 3:20 p.m. Monday about two miles south of Haines. 

At least 47 other people filed “Felt It” reports with the Earthquake Center and United States Geological Survey, and dozens weighed in on social media. 

An unusual lag time occurred between when the earthquake happened and when seismic monitoring data became available. 

Initially, Alaska Earthquake Center communications manager Elisabeth Nadin said they had no record of an earthquake in the region. 

She said a glacial calving event or road construction could lead to the kind of rattling residents reported. 

“Those are still things that we tend to pick up,” Nadin said. 

But people who picked up the phone at both HiEx construction and Southeast Roadbuilders in Haines on Monday said no such activity was happening. 

With a lack of data, people began theorizing about what it could have been. Based on accounts from people living between Juneau, Haines and Skagway – depending on where people were they  either heard or felt the earthquake first.

Skagway borough finance employee Juliene Miles said she heard “a rumble and then a boom and the building shook. All the windows were rattling in city hall.” 

Miles said people in Skagway thought a jet scrambling caused a sonic boom, a phenomenon she’s familiar with from her time living in Seattle. 

Jim Stanford, who lives in the upper Chilkat Valley, felt that could be a plausible theory as well. He also said he heard what sounded like a boom. 

“We’ve had low-flying, I think they’re fighter jets flying all over the mountains and low,” he said. “Yesterday, they were all over the place. I don’t know whether they were just performing some kind of drills? I heard them six or seven times.”

Others in Haines said they thought a tree had fallen or a vehicle crashed into their home. 

A few hours later, Nadin called back with an explanation – what people felt likely was an earthquake that missed by the center’s auto-detection at first. She attributed that, in part, to the low number of seismic stations in the area. 

“It’s on the edge of the network,” she said. 

There is one seismic station in Skagway, a partner station at Pleasant Camp in British Columbia, one north of Juneau at Bessie Mountain, then farther afield, one in Atlin, British Columbia, and one in Deception Hills South of Yakutat. 

“There are, kind of, four in the immediate area and to do a precise location we try to rely on something like six stations,” Nadin said. 

So, the precise location of the earthquake was not reported until nearly an hour after the initial earthquake. Data from the earthquake center shows that it was about seven miles deep, contained within the continental crust. 

Nadin noted that it was located along the Chilkat River section of the Denali Fault, which is a strike-slip fault, meaning it moves horizontally. 

“Everything west of the Denali fault is moving north,” she said. “Everything East of the Denali fault is moving south.” 

She also offered an explanation as to why some people heard the impact of the earthquake before they felt it. That phenomenon can be explained by a person’s distance from the earthquake and the seismic waves generated by one. Primary, or “P waves” move through the solids, liquids and gases, while secondary or “S waves” can only move through solids. P waves are faster, and while they cannot be felt, they can shift things around, which can cause an audible noise. 

“They’re not waves that cause shaking. That could explain anything that people sensed before they felt shaking,” Nadin said. 

S waves are slower and cause the more intense shaking people feel. Because of that difference in travel speed, the farther someone was from the epicenter of the earthquake, the more likely they were to hear something – because of the P waves – before they felt something – because of the S waves. 

Back at Philpott’s home, he didn’t follow up with officials to find out more about the unusual waves on the surface of the Chilkat River. But he did call his friend Tim Ackerman. 

“He just wanted to know what was happening and if we had felt anything down here,” Ackerman said from his Fort Seward-area home. 

“We’re on bedrock kind of right here at the fort and it’s a different strata,” he said. 

Ackerman said he was standing in the kitchen with his wife, April Ackerman, and a friend Dory Thompson when the rattling started. 

“You could hear all the glassware clanking together in the house,” he said. “It almost sounded like a gust of wind, he said. “We were trying to figure out whether the earth and its movement was causing the air to react. It was almost like a shockwave.”