An earthquake centered in Canada could be felt by some people in the Pittsburgh area this afternoon.
Reports of buildings shaking came from Carlow University in Oakland and from the South Side, among other locations.
The U.S. Geological Survey reported the magnitude 5.5 quake was centered at the Ontario-Quebec border at 1:41 p.m. It was felt a few minutes later in Western Pennsylvania. Pittsburgh police said they have no reports of damage.
News reports said it also could be felt in New York City, New Jersey, Ohio, and Michigan.
Buildings shook in Toronto for almost a minute and several were evacuated.
Like most people who felt the slight tremor in the Pittsburgh area, Wendy Graves, an editor at Akoya, a communications consulting firm on the South Side, wasn't sure what it was right away, having never been through one before.
"I felt it shake my chair three times, with a few seconds in between each one," said Ms. Graves, 45, who was working at her job on the second floor of a building on East Carson Street when she felt it at about 1:44 p.m. "After the third one I said jokingly, 'Is that an earthquake?' "
Barbara Olson, a retired cruise consultant who lived in the Los Angeles area for nine years before moving to her present home in Sewickley in 1992, thought she recognized the swaying motion she felt as she worked on her home computer, but she didn't believe it.
"My first sensation told me, 'This is an earthquake,' " she said, but she and her husband, George, had moved to the Pittsburgh area expecting to escape them.
It wasn't until a neighbor called to see if she had felt it, too, that she believed it.
"It was a big relief because you think you're going crazy," Ms. Olson said with a laugh.
Once Kate Burroughs and her colleague at the Association of American Cancer Institutes, Sara Arvay, confirmed with each other that they were feeling their building on Fifth Avenue in Oakland sway, they didn't check with anyone else; they exited from their fifth-floor office for 15 minutes until they were sure it was over.
"At first I thought, 'Huh, this is kind of weird. I'm trying to diet so maybe I'm a little light-headed,' " Ms. Burroughs, 54, said. "But I asked Sara and she felt it, too."
The earthquake originated in an area called the Ottawa River Valley, where huge plates that make up the continent sometimes slip.
The quake likely was caused by a process called "post-glacial rebound," said Russel Pysklywec, a University of Toronto geologist who said he felt the quake and immediately knew what he was feeling.
"About 10,000 years ago there were glaciers covering us. That ice subsequently melted and the plates are now rebounding upward," Mr. Pysklywec said. "Normally those stresses are relaxed fairly quietly."
He placed the earthquake's depth at 19 kilometers and said the shaking in Western Pennsylvania was the shock rippling outward. By afternoon's end, he said, the quake would be measured on instruments in Australia, "like an ultrasound of the planet itself."
Little damage was reported in Canada, according to early reports, though the quake's reach served a reminder that even in the geologically placid northeast, the Earth still packs the occasional wallop.
"It's kind of a neat thing in some ways. It shows us how much energy there is in the planet," said Mr. Pysklywec.