The deafening blast 50 feet behind Boston Marathon runner Tami Hughes jolted her right back to Sept. 11, 2001.

"In the three seconds that it took me to turn around [last Monday], at first I'm like, 'Oh God, did a plane crash into a building?'" said the Darien resident, who no longer works in New York City as she did in 2001. "I jumped out of my skin. I threw whatever was in my hand."

Like Hughes, many in Connecticut revisited feelings this week related to previous traumas, whether it was the Newtown school shootings, the 9/11 attacks or another incident. The anxiety of being under attack, unsafe and threatened was re-awakened by this week's events and 24-hour news coverage.

A general sense of vulnerability and uncertainty was heightened by news that ricin-laced letters were sent this week to President Barack Obama and U.S. Sen. Roger Wicker, a Mississippi Republican, and the wild manhunt that ensued Thursday and Friday in Cambridge and Watertown, Mass.

What's different in the post-9/11 era is that many Americans have mental and emotional reference points for what happens after an attack from an unknown assailant intent on killing random civilians. For some, there's even a resolve to carry on and not be afraid of airports, parades, ball games, city streets or other places an attack could happen.

Hughes says she was watchful in crowded, public places for years after 9/11, but the vigilance waned with time. The marathon bombs brought back the initial terror, and then a familiar awareness and caution.

Hughes, 43, worked on the trading floor in fixed-income sales for Merrill Lynch at the World Financial Center, near the World Trade Center. By chance, she was home in Connecticut for 9/11 — her birthday — but Hughes was worried for hours about the safety of her co-workers and the man who would become her husband.

Those feelings rushed back Monday.

Hughes was at the marathon finish line when the first bomb erupted on Boylston Street just west of Copley Square. Only seconds after the first boom, her mind jumped to her young children, who were with a friend in a car at Copley Square. Hughes ran away from the site, south on Dartmouth Street and borrowed a cellphone so she could text her friend to get the children out of the city. Then she dashed into her hotel, got her luggage and waited for her husband, Danny, to meet up with her.

The family escaped uninjured, though far from unaffected.

"We're better prepared today to react to things like that," Hughes said. "It is a new reality. I think it's going to bring people back. I think we're going to be more cognizant. Do I bring my 4-and-8-year-olds into this very crowded place?"

Accidental Versus Intentional

Two days after the marathon bombings, an explosion ripped through a fertilizer plant in Texas, killing at least 14 and injuring about 200. Horrific as this was, the event didn't provoke the same national emotional response as the marathon bombings. A large part of this has to do with the sinister intent behind the latter, psychology experts say.

"The most immediate threat to our survival is if someone else is attempting to attack us," said Julian Ford, a psychologist at UConn. "It's clearly a very biologically hard-wired instinct to survive and protect."

And while the victims of the fertilizer plant explosion were mostly limited to a specific geographic and demographic group, the marathon bombings emphasize the fact that terrorism can happen to anyone at any time. An 8-year-old boy, a 29-year-old restaurant manager and a graduate student from China were the three people killed Monday in Boston. Those injured, many of whom had traveled a long distance to get there, were equally varied in their backgrounds.

Also, fertilizer plants bring with them an understood risk linked to hazardous chemicals. Bridges collapse and waterfront homes face flooding. It doesn't make it any less tragic when these things happen, but it does make it less shocking, they say.

"But at a marathon, everyone's guard is down, it's celebratory, so [the bombing] feels like a blindsiding," Ford said. "An elementary school is one of the safest places we have. We have to believe our schools are safe because we trust our children to them, and for the most part, they do an exemplary job."

That's what makes terrorism such an effective weapon.

Ten times as many people are killed in motor vehicle accidents in the U.S. every year as were killed in the 9/11 attacks, but 12 years later, that day still resonates —all the more so in recent days.

Yuval Neria, a Columbia University psychologist who has been studying post-traumatic stress disorder in people and who closely experienced the events of 9/11, said that with each tragedy of this kind, our responses improve on a practical level. Emergency workers are better prepared, and security officials identify vulnerabilities and safeguard against future attacks.