RICHMOND (Va.) – On Tuesday, August 23, 2011 a “Moderate” earthquake centered near Richmond, Va. shook much of the East Coast and parts of Western New York.
At 1:51 p.m., the earthquake occurred near Mineral, about 38 miles northwest of the City of Richmond, four miles deep into the Earth’s crust, sending out seismic waves that were felt for hundreds of miles in every direction.
The quakes’ final rating from the United States Geological Survey was a 5.3 on the Moment Magnitude (Richter) Scale, making it the strongest earthquake to occur east of the Rocky Mountains since the 1944 M5.8 Massena, New York earthquake.
Officials with the USGS believe this earthquake to be the largest quake felt in United States history, with over 140,000 people reported feeling the ground shaking to the “Did You Feel It?” page of the USGS website. Tremors from the earthquake were reported as far south as Atlanta, Ga., to as far north as Quebec, Canada.
Humans were also not the only ones who were startled by the quake. Officials at the National Zoo in Washington, DC said the animals started exhibiting strange behavior seconds before the earthquake occurred. In a press release, zoo officials noted the quake occurred during routine lunchtime feedings with many of the apes abandoning their food and climbing to the top of a tree about 5 to 10 seconds before.
The earthquake occured within the Virginia Seismic Zone, a spot that is known for letting out tremors. The Zone was created during a continental collision between the North American and European continents over 200 million years ago when the Pangaea supercontinent and the Adirondack Mountains were formed. As a result of this collision, there are many seismic faults that line the East Coast of the United States but for the most part, those faults stay dormant.
However when one of those faults do become active, it is not uncommon for tremors to be felt over long distances. Earth rock within the crust on the eastern half of the country is older and harder than the rock composition on the West Coast. Earthquakes out there aren’t felt as widely due to cracks and faults in the stretched and softened crust, acting as barriers that absorb most of the energy.
On the East Coast however, the denser profile of the bedrock allows seismic waves to travel freely as there are little natural barriers in the way to disrupt the flow of the waves.
Damage from the earthquake was the greatest in Louisa County, VA, the location of the epicenter, where two buildings and the ceiling of the Town Hall collapsed in Mineral. Damage also occurred in the Nations Capital where the Washington Monument and the National Cathedral sustained damage, along with several buildings. Other minor damage occurred in several other states that felt the earthquake.