Quake sets the Northeast aquiver

For a region unaccustomed to quakes, the rumblings, while brief, left a tangible sense of unease that lingered long after any danger had passed.

Some, like Cassandra Barnum, a law clerk working on the eighth floor of the federal courthouse in South Boston, first suspected that the building had been bombed.

“I was nervous,’’ the 26-year-old said. “The building was swaying, and everything was off balance.’’

Fellow law clerk David Seligman was at his desk when the building started to shake, and his mind raced for a reason.

“I was pretty sure I was having a panic attack,’’ he said.

Damaris Ortiz, an employee at a Target store in Dorchester, was in the break room when the table began to shimmy.

“The guys all started screaming,’’ she said. “People were like, ‘ Why are we all getting dizzy?’ ’’

Fearing the worst, Tina Cassidy, vice president at Solomon McCown & Co., told colleagues to leave the downtown building.

“I thought there might have been an explosion or the building was collapsing,’’ Cassidy said. “Earthquake did not enter my mind.’’

As the initial bewilderment faded, people quickly swapped stories about their shared experience. Many rushed to Facebook and Twitter to share and even to crack jokes.

“Earthquakes, shark sightings, and nice weather … when did Boston turn into Cali??’’ wrote Pat Connolly of Medford, 28, a physical trainer.

Massachusetts lies in a moderate earthquake zone and experiences several small tremors each year. Scientists cite the Cape Ann Earthquake of 1755 (with a magnitude of at least 6.0) as the last major earthquake to cause significant damage here.

Yesterday, the tremors seemed to affect the area unevenly. While residents on Savin Hill felt shaking for about 10 seconds, people on Castle Island felt nothing, a pattern repeated across the area.