That shake you felt Friday morning was only the Earth's crust settling like an old home.
A 5.1-magnitude earthquake west of Ottawa, Canada, did not cause damage to the areas surrounding the epicenter nor to Scranton, but was felt by many just before 10 a.m., according to The Associated Press and a local geology expert.
A 4.8-magnitude quake was centered near the town of Braeside, Ontario, the AP reported.
Northeast Pennsylvania is far removed from major continental plate boundaries, where many of the world's most violent earthquakes occur. When the area shakes, it is due to "intraplate" activity, or movement within a tectonic plate, and it is almost always a small event, except for very rare occasions, said Ian Saginor, Ph.D, assistant professor of earth science at Keystone College.
The last time the area felt an intraplate tremor was on Aug. 23, 2011, when a 5.8 magnitude earthquake in Virginia took many area residents by surprise.
There is a misconception that a continental plate is a solid or uniform sheet of rock, Dr. Saginor said. In reality, a continental plate is a motley collection of rock sutured together over billions of years with each part subject to its own settling.
"It's like a house settling," Dr. Saginor said. "It doesn't mean this house is going to fall apart."
Just like a continental plate is a collection of rocks, the reason why any one earthquake occurs is the sum of many parts.
Dr. Saginor speculates another part of Friday's earthquake stems from Canada's crust finding a level of balance, having been relieved of a mile of thick sheets of ice in certain areas from the last ice age. Dr. Saginor likened the affect the weight of that ice had to the affect heavy cargo has on a boat. When the cargo is saddled, the boat sits low in the water and when the cargo is lifted, the boat sits higher. In Canada, the Earth's crust has been slowly rising for 18,000 years and the movement contributes to intraplate earthquakes.
"When you remove all of that ice, it's like the ground is actually rising," Dr. Saginor said.
Contact the writer: jkohut@timesshamrock.com, @jkohutTT on Twitter