A rumble, and then the floor jerked, and Sarah Saadian, a block from the White House, had one thought: Terrorism.

Konnie Hooton felt the shake and instantly assumed “an attack.”

Lacey Boling was in a room with 25 others. When everything went jittery, she figured the Metro, several stories below, had been blown up.

In Washington, 10 years later, every day is Sept. 12. When the office ceiling shifts to and fro, and the pens and cups fall off the desk, it’s scary enough. But in a terror-scarred city, thoughts go immediately to evil attack rather than natural disaster.

John Williams was working construction on a building across from Lafayette Park when the earthquake hit Tuesday afternoon. “I thought it was a terrorist, being here where we are,” he said. It wasn’t until he got onto the sidewalk that he saw the news of the quake on his cellphone.

Saadian, who works at the National Community Reinvestment Coalition, near the Treasury Department, said that at first, the panic in the office felt like Sept 11. People streamed onto the street, and only then did she register that this was no man-made event: “Once I saw people chatting, I knew it was okay. Because on September 11th, it was just silent — quiet and creepy.”

People looked up at the sky for smoke. They listened for sirens. They checked their colleagues for signs of that gut-level fear they had felt a decade ago. Same clear blue sky, same blessed break from the humidity.

This time, the throngs of people crowding street corners and parks were talking nonstop — a far cry from that shocked silence in 2001. They were trying in vain to call spouses and children and parents and friends. (Sprint Nextel declared the quake a “temporary mass calling event.”) They were trading stories about earthquakes, hanging on every word of knowing Californians. They were shaken but relieved.

“When we didn’t hear sirens, I knew we were okay,” said Hooton as she waited for a bus home to Leesburg.

Daniel Herschberg and his family were on a platform at the Woodley Park Metro station when they felt the rumble. Tourists from Long Island, they didn’t know what to make of the feeling. Herschberg’s first thought was, “Maybe this is something that happens around here, like some sort of Washington protest march outside.”

His daughter Tamar, 9, said, “We thought it was the train going through the tunnel.”

But her father’s thoughts quickly moved on to dirty bombs and the like. “You’re deep down there, and this is Washington,” he said. Only jokingly, he told his family that the rocking might be an earthquake.

Their train arrived and they traveled downtown, only to find that their 3 p.m. appointment for a White House tour was canceled. “Forget it,” a Secret Service officer told them.

“Took us six months to get that appointment,” Herschberg said.

Downtown quickly took on a look very much like that of Sept. 11, with gridlock, blinking traffic lights, Metro platforms overflowing with passengers and hundreds of people standing on street corners, waiting. Hundreds more gave up on transit and hoofed it home.

Smartphone-armed workers texted babysitters and day-care centers. “They say we can’t go back into the building,” one worker announced to a clot of 18 colleagues, winning a cheer. The queues for the buses to Loudoun County formed a couple of hours earlier than usual and snaked around a corner — everyone was trying to get home at the same time.

When people could get through to family and friends, the instant parlor game was to see who could find the farthest reaches of the quake. “Toronto!” one woman said. “New Hampshire!” a man replied.

But that was after the fright had subsided. In the moment, foundations shook — not only of buildings, but of people who have felt shaken too often, people always on edge, perpetually living the day after. At Inova Fairfax Hospital, doctors reported broken-bone cases involving people who felt the quake and jumped out windows.

“I felt that same extrasensory thing as on September 11th,” said Saadian, of Falls Church. “That feeling that something is happening, something out of control.”