When tragedy grips the nation — tornadoes in Oklahoma, a bombing in Boston, a school massacre — the banal conversation on Twitter and Facebook morphs instantly.

People post news and photos of the victims. Many tweet condolences. Others fall silent. It's like a very public, very noisy memorial service.

At the same time, some still stick to sharing cat videos, which offends some mourners.

This confusing collision of conversations is raising questions about the emerging etiquette of tweeting during tragedy. What is appropriate? What if you don't tweet anything at all? Does that signal you don't care?

It's a dilemma giving some Twitter users pause. Marina Maric of Minneapolis has been tweeting since 2006, yet she still wonders what to say when catastrophe overwhelms her feed. Before she knew that an F-5 tornado had ripped through Moore, Okla., on May 20, she posted a joking tweet about her hotel in Portland. But when she read about the disaster, she worried that her previous tweet might have seemed flippant.

Soon, she posted: "I was up in the air all day ... catching up on the news from Oklahoma just now. How sad."

The deadly tornado that struck near Oklahoma City late last week was 2.6 miles wide, the widest ever recorded. Once the news spread, many tweeters that day moderated their posts in light of the tragedy.

The sentiment was genuine, she said, but also an attempt to comply with this evolving etiquette.

"I did at some point think, 'People are going to think I'm insensitive,' " Maric said. "I needed to acknowledge to the world that I knew something had happened."

She had good reason to be worried.

Heightened reactions

Backlash from the public has made it clear that businesses and brands should quiet their social media marketing after tragedy, experts say.

American Apparel's "Hurricane Sandy Sale" drew intense criticism. So did a tweet by Kenneth Cole, joking that the uproar in Cairo during Arab Spring must've been related to the release of the brand's spring collection. Social media users pounced on foodie website Epicurious for tweeting a recipe for whole-grain cranberry scones "in honor of Boston and New England" after the marathon bombing.

"If you're selling candy or clothes or something like that and you're trying to weave something in, that's not the appropriate time," said Joel Carlson, owner of social media consulting firm Sociability.

But what's the average person to do when Twitter or Facebook is overwhelmed by sorrow?

"There's a simple solution to this: What would you do in real life?" said Lisa Grimm, of digital advertising agency Space150 in Minneapolis.

The online conversation, while a great outlet for people who want to connect with others after tragedy, exemplifies the different ways people deal with grief, said Jennifer Baker Jones, a psychologist with the Center for Grief, Loss and Transition in St. Paul.

"People have their own rules," she said. "Not everyone's comfortable saying what they feel, even if it's a condolence posted on Facebook."

Karl Pearson-Cater of Minneapolis said it can be tricky to mix heavy emotions with the everyday levity of social media, especially Twitter.

"I'm sometimes so stunned by [a tragedy] that I don't end up tweeting because I'm processing," he said. Other times, "I don't feel like I need to say something."

Mostly he keeps using social media as he would any other day.

"You should just do what feels natural to you," he said.

To tweet or not to tweet

For Arik Hanson, owner of Minneapolis-based ACH Communications, that usually means keeping his thoughts on tragedies to himself rather than joining the online discussion.

"I will rarely, if ever, discuss politics or religion. This kind of falls almost in that camp," said Hanson, who did not tweet anything about the deadly tornado even though his Twitter feed was filled with condolences and well wishes.

"It's not because I don't care," he said. "I don't feel like I have that much to add."

But Shakopee Mayor Brad Tabke, who was immersed in social media chatter about the Minnesota Legislature when the tornado tore through Moore, thought it was important to acknowledge the event, tweeting: "Thoughts and prayers are with the victims and public safety workers in Oklahoma. Tragic story."

He also retweeted condolences from the Scott County sheriff and a message from Willie Nelson explaining how people could donate to the Red Cross by text.

"From a leadership standpoint, it's important to make sure people know that you care," Tabke said. "If it were my community that were the subject of some disaster, I would hope that people would recognize that, as well."

But he didn't pull back from the social media conversations about the Legislature.

"It's important to be respectful of what is going on," he said. "But it doesn't mean all lives around the world need to stop."

Katie Humphrey • 612-673-4758