The latest in a series of minor earthquakes in
northeast Ohio hit on Saturday, sending some stunned residents running for cover as bookshelves shook and pictures and lamps fell from tables.

The 4.0 magnitude quake struck Saturday afternoon in McDonald, outside of Youngstown, the U.S. Geological Survey said. Area residents said a loud boom accompanied the shaking, but sheriff's dispatchers from several counties in the area said there were no immediate reports of damage. A few miles from the epicenter, Charles Kihm said he was preparing food in his kitchen when he heard a noise and thought a vehicle had hit his Austintown home. "It really shook, and it rumbled, like there was a sound," said Kihm, 82. "It was loud. It didn't last long. But it really scared me." The area has experienced at least 10 minor quakes in 2011, though Saturday's temblor appeared to be stronger than others, which generally had a magnitude of 2.7 or lower. This time, some residents reported feeling trembling farther south into Columbiana County and east into western Pennsylvania.
Many of the quakes have struck near an injection well used to dispose of brine water that's a byproduct of oil and gas drilling. Thousands of gallons of brine are injected into the well daily, and much of it is shipped in from out of state. Its owner, Northstar Disposal Services LLC, has agreed to stop injecting brine into the earth as a precaution while authorities assess any potential links to the quakes. The head of the Ohio Department of Natural Resources said research hadn't led to a direct correlation with the injections but officials wouldn't gamble with public safety. There are 177 similar injection wells around the state, and the Youngtown-area well has been the only site with seismic activity, the department said. Patti Gorcheff, who lives about 15 miles from the epicenter, said her dogs started barking inexplicably Saturday and the ornaments on her Christmas tree began to shake. Her husband thought he heard the sound of some sort of blast. "This is the biggest one we've had so far," said Gorcheff, a North Lima resident who has raised concerns about quakes and drilling-related activity in the region. "I hope this is a wake-up call." - USA Today.

According to the
USGS, the Northeast Ohio seismic zone has had moderately frequent earthquakes at least since the first one was reported in 1823. The largest earthquake (magnitude 4.8) caused damage in 1986 in northeasternmost Ohio, and the most recent damaging shock (magnitude 4.5) occurred in 1998 at the seismic zone's eastern edge in northwestern Pennsylvania. Earthquakes too small to cause damage are felt two or three times per decade. Earthquakes in the central and eastern U.S., although less frequent than in the western U.S., are typically felt over a much broader region. East of the Rockies, an earthquake can be felt over an area as much as ten times larger than a similar magnitude earthquake on the west coast. A magnitude 4.0 eastern U.S. earthquake typically can be felt at many places as far as 100 km (60 mi) from where it occurred, and it infrequently causes damage near its source. A magnitude 5.5 eastern U.S. earthquake usually can be felt as far as 500 km (300 mi) from where it occurred, and sometimes causes damage as far away as 40 km (25 mi).
Earthquakes everywhere occur on faults within bedrock, usually miles deep. Most of the seismic zone's bedrock was formed as several generations of mountains rose and were eroded down again over the last billion or more years. At well-studied plate boundaries like the San Andreas fault system in California, often scientists can determine the name of the specific fault that is responsible for an earthquake. In contrast, east of the Rocky Mountains this is rarely the case. The Northeast Ohio seismic zone is far from the nearest plate boundaries, which are in the center of the Atlantic Ocean and in the Caribbean Sea. The seismic zone is laced with known faults but numerous smaller or deeply buried faults remain undetected. Even the known faults are poorly located at earthquake depths. Accordingly, few, if any, earthquakes in the seismic zone can be linked to named faults. It is difficult to determine if a known fault is still active and could slip and cause an earthquake. As in most other areas east of the Rockies, the best guide to earthquake hazards in the Northeast Ohio seismic zone is the earthquakes themselves.