"It's very rare in that area to have an earthquake," said Waverly Pearson, a geophysicist with the National Earthquake Information Center, Golden, Colo. "It hasn't happened very often over the years in that area so there's a lot of excitement for a moderate quake."
John Houlihan, a professor at the Pennsylvania State University's Shenango Campus, said the quake was minor and a damaging earthquake in this area is not likely.
"I don't want to trivialize it, but this was pretty much a minor quake," Houlihan said. "As long as they don't get much above a six we'll be OK."
Friday's quake registered 5.2 on the Richter Scale while the 1989 San Francisco earthquake registered above 8. The tremor in 1986 quake registered 3.2. The Richter Scale increases exponentially; each whole-number increase means 10 times more intensity.
An earthquake of 3.5 on the Richter scale can cause slight damage, 4 — moderate damage, 5 — considerable damage, 6 — severe damage.
A 7 reading is a "major" earthquake, capable of widespread heavy damage. A reading of 8 is a "great'' quake, capable of tremendous damage.
"We have almost no active faults in this regions," he said. "This is one of the more geologically stable areas in the United States."
Active fault lines include those that have some sort of tremor weekly.
About seven or eight major tectonic plates on the North American plate, which covers most of the United States. When those plates meet fault lines are formed, Houlihan said, adding that when the Pacific plate met the North American plate, the San Andres fault was formed.
Faults that affect this area run from St. Louis, Mo. to the Hudson River Valley in New York state and to New Hampshire, and the Lewis Overthrust, or Logan's Line, from the northeastern United States to the Gettysburg area in Pennsylvania.
"Minor faults are all that exist in this part of the country," he said. "You have deep level faults as opposed to shallow faults."
Houlihan said Friday's shake up was a deep level fault.
"I've lived here for 30 years and this is only the second tremor that I've felt," he said. "In California they have a tremor of this magnitude on a bi-weekly basis."
Pearson said it's highly possible that the same fault caused the quakes on Jan. 31, 1986, and Friday, but more research would have to be done to determine that. The epicenter of the 1986 quake was in Ohio about 40 miles on northwest of Friday's.
Pearson said no on can predict and earthquake, and any hints that this a precursor to something bigger to come in the coming century are off base.
Houlihan said if there are aftershocks, they will not be that severe.
If the tremors do become severe, people should seek shelter under a door frame or another structurally sound area, Houlihan said. People should use caution if going outside during or following a tremor because of downed utility wires.