First, there was a jolt. Next came a deep, unsettling rumble. And then more jolts. Was it an attack? Construction? A passing train? Minds raced as folks across the region dived under desks, ran to doorways and ultimately poured into the streets.

On Aug. 23, 2011, at 1:51 p.m., seismic waves pulsed outward from the earthquake epicenter in Mineral, Va. The fracture occurred in the Central Virginia Seismic Zone, a region of numerous small faults in the Piedmont of the state.

The 5.8-magnitude earthquake, which took place four miles deep, was the strongest to hit the region in the modern record, as well as the strongest east of the Rockies since 1944. It is believed to have been the most-felt earthquake in U.S. history. About one-third of the U.S. population was in areas where shaking was noted.

The shaking lasted less than a minute, but it was felt in every state on the East Coast from Florida to Maine, as well as into the Midwest and parts of Canada. Reports came in from places like Rehoboth Beach, Del., New York City and even Chicago and St. Louis.

This large footprint was due to a difference in soil and subsurface rock in the East compared with the West. Earthquake waves travel farther on the East Coast because there is less broken bedrock, which tends to stifle quake waves. The relatively undisturbed soils of the eastern United States helped the shaking to be felt far and wide.

Once the shaking stopped, light to moderate damage was reported across the region — along with a lot of frayed nerves.

For many people, it was their first big earthquake. For others, mainly those who lived in earthquake-prone areas before coming to the Mid-Atlantic, it didn’t take too long to figure out what had caused the rocking and rolling.

Damage was somewhat widespread, given that most buildings in the area are not built to take a large quake. The damage was generally minor, but there were notable exceptions.

The worst of it was near the epicenter between the Spotsylvania Fault and Chopawamsic Fault. Several minor injuries were reported in and around Mineral, Va., where at least two buildings collapsed and many other structures were damaged, including chimney falls.

Structural and infrastructure damage was reported in Charlottesville, Culpeper and Fredericksburg in Virginia; the D.C. area; and even up into parts of northern Maryland, Delaware and West Virginia. In Washington, items were tossed off shelves and some furniture toppled. Significant damage to the Washington Monument and Washington National Cathedral caused extended closures of both.

Scars remain at Washington National Cathedral, which took 87 years to build. The quake required $34 million in repairs that are ongoing today. Reports indicate that the work is about half-completed. As bad as it was, it could have been worse if the earthquake had continued much longer.

As someone who grew up in Southern California, I have felt big earthquakes, but I was still surprised. It took me a few seconds to realize what was happening and I quickly thought, “Hopefully this doesn’t get much bigger.” When I saw my constantly working boss at my job at the time flying through the hall to get out of the building, I knew it was serious.

Needless to say, folks who were here for the earthquake still remember it vividly.

At Capital Weather Gang, we asked our friends on Twitter and Facebook to share their recollections. Reactions from the time included fear, pure confusion and even delightful irony. The recollections were too many to reproduce here, but we’ve enjoyed reading them nonetheless.

“I was on the epicenter. Was in high school at the time in Louisa County and the school was falling in on our heads. Had to take cover under desks and hope for the best,” tweeted Jason Conner.

“I was walking near Farragut Square when a huge boom sound went off. Everybody on the street looked at one another,” wrote Brian Noyes on Facebook.

Many people recalled thinking the earthquake was a terrorist attack, as the event occurred just weeks before the 10th anniversary of the 9/11 attacks.

“I was on the 9th floor of my office building in Crystal City. It was a weird day. Metro closed. Took the bus home early and walked a few miles to the apartment. Everyone in the office was talking about 9/11 recollections,” tweeted Liz McCarthy.

Erin Pollard shared a similar experience: “I was working near Union Station and the Capitol. We all rushed out assuming it was a terror attack. I remember running down the block trying to find the smoke. Earthquake was not on our radar as a possibility.”

“As soon as I felt the tremor, my brain shouted ‘bomb’ and I ran like hell. I sat near the stairs and was the first one out. I’m a big dude, but I got after it. The security guards saved the footage for months and would play it when I walked by,” wrote John Hagner.

“I went into the hallway just as the whole building started to shake. We evacuated thinking it was a terrorist attack,” said Jesse Busen on Facebook.

There was general confusion amid loud noises and unsettling rumbles, and people poured into the streets.

“I was in the house, and heard it before I felt it. I ran outside, and it seemed like the sound was coming from everywhere,” said Dee Tomczak on Facebook.

“I was at work at Dupont Circle. A noise went through the ceiling tiles above me like someone was pulling cables through,” wrote Margaret Banks Jolly.

“I was on the 12th floor of an office building in downtown Baltimore. The entire building swayed,” tweeted Battling Maxo.

“I was on the 12th floor of a building in Tysons. Knew what it was straight away. Looked out the window and saw the glass on a neighboring building rippling like waves on an ocean,” wrote Danosaur on Twitter.

There were also people who felt the earthquake before their family or friends did elsewhere.

“About 2 minutes later my dad called back and was like, ‘Did you just feel an earthquake???’ Shortly after I hung up it hit there!” noted Amanda Marie Morris, who was in Arlington. Her dad was on Long Island.

Pat Soriano shared a similar experience: “I was in Connecticut and felt my desk shift slightly under my papers as I was on a call with D.C. colleagues. One person in D.C. said that’s an earthquake, call is over, we need to evacuate.”

And then again, some people didn’t notice it at all.

“I was maybe the one person in D.C. at the time that missed it completely. I was swimming laps at Haines Point. I felt nothing as the water doesn’t change,” wrote Kyle Simpson in an email. “Getting home on bike was nuts. People everywhere.”

A weird day for sure. Let’s hope we don’t repeat it any time soon.