Earthquakes usually are not a common occurrence here in Ohio. But, the state just experienced its 10th earthquake of the year, almost all of them happening under and around Lake Erie. This week's quake was the largest of the year. Although it was only a 3.8 magnitude quake, it gave many in northeastern Ohio an afternoon jolt.
Ohioans generally don't have to worry too much about earthquakes. But recently, earthquakes have become almost commonplace in northeastern Ohio. Of the 10 earthquakes in Ohio this year, nine of them happened around the same general region around Lake Erie. The most recent quake occurred Tuesday about 40 miles east of Cleveland. It was centered in Lake Erie, just three miles from the village of North Perry. It was a minor quake that did not result in any reported damage.
The earth shook at around four o'clock.
"There definitely was a rumbling that scared me," said Perry, OH florist Sharon Redlin. She was napping in her home.
"I was laying on the couch almost snoozing, and I actually felt movement, and it was kind of a loud rumbling sound was what I heard."
At first, Redlin thought it might've been the noise of nearby construction work.
It's still unknown what this recent increase in seismic activity may mean. The Ohio Seismic Network monitors seismic activity throughout the state. Network Coordinator Michael Hansen says there's a sense of complacency in Ohio about earthquakes because they are relatively rare. Big, damaging quakes in the Midwest may be separated by decades, centuries, or even thousands of years. But Hansen also notes there have been about 200 earthquakes in Ohio since 1776, when people first began recording them.
Only within the past few years have scientists begun to really learn about Ohio's subterranean rumblings.
"This is the first time we've had state-wide monitoring of earthquakes and we're not only recording more earthquakes, but we're really beginning to learn a great deal about what is beneath us," Hansen says.
The first seismic monitor was installed in 1999, when funding first became available to monitor state-wide activity. With each earthquake, scientists can map fault lines that run through the state. They cannot predict when an earthquake might occur. But Hansen says once they collect more data about fault lines, they might be able to predict how big an earthquake could be.
Still, Ohioans won't have to worry as much as people who live in places like the west coast, where there are frequent and severe earthquakes.
Places with a lot of seismic activity are where separate tectonic plates meet. Tectonic plates make up the Earth's surface, and when they move and rub against each other, they cause earthquakes. The boundary of the tectonic plates forms a deep cut into the Earth's surface. Hansen says these sorts of deep geological cuts once existed in Ohio about a billion years ago. Now, all that remains are scars. And it's these ancient scars that are the current cause of seismic activity in Ohio.
"These are ancient features that are buried deep beneath us. Limestone and shale and so on cover these things over. But these are zones of weakness, and as the Atlantic ocean gets wider along the mid-Atlantic ridge, it's pushing the North American continent westward so those stresses are accumulating in the continent and they're relieved along these ancient zones of weakness," Hansen says.
He says the accumulating stress can cause slippage of the rocks, leading to earthquakes. Although we probably don't need to worry about a massive earthquake in the near future, we don't know anything for sure. "There probably is a low probability of a damaging earthquake in the state, but it certainly isn't a zero probability," says Hansen.
The largest earthquake recorded in Ohio occurred in 1937 near the western Ohio town of Anna. It had a magnitude of 5.4, damaging chimneys, and cracking walls and foundations.