Kyle Cassidy could swear he had just felt an earthquake, so he stepped outside his West Philadelphia home to seek confirmation from a neighbor.

Nah, his neighbor said. It was probably just construction.

That explanation might have sufficed if not for the thousands of tweets that also swore to have just felt an earthquake. The photographer/designer walked back inside and saw reports from Maine to South Carolina, all with a shared bewilderment in the instant realization that they were not alone.

"We have become this collective entity," Cassidy said, finding out from each other "more quickly than the U.S. Geological Survey, or someone right next to me, what had happened.

"We're all little USGS sensors right now."

With the quake still rumbling, some Facebook and Twitter users started to post in present tense: Does anyone else feel this?

"To know that someone outside of our building, or in another city, or in an office down the street is experiencing the same thing is something you can't get other places," said Mindy Yablonski, 29, who was on the 35th floor of a Center City high-rise.

Of course, once it became apparent that everyone was safe and there was no major damage, confusion quickly turned to snark.

"Everyone used Twitter to discuss the earthquake, and now everyone is using Twitter to make fun of everyone who used Twitter to discuss earthquake," tweeted Drew Lazor, an editor at City Paper.

"Everyone relax . . . it wasn't an Earthquake . . . Arlene Ackerman just dropped her buyout check & it hit the floor. Resume operations as normal," quipped Victoria Parrilla of Philadelphia.

It was a far different story after the tsunami in Japan, when social media was a primary source of communication. Google set up a "Person Finder" Web app to connect victims and family. There were more than 1,200 tweets per minute from Tokyo less than an hour after the earthquake, according to Mashable. Thousands of amateur videos on YouTube showed the destruction.

After Tuesday's earthquake, news of SEPTA delays and grounded airplanes at Philadelphia International Airport appeared first on Twitter. Philadelphia police reiterated in a tweet: They were aware of the earthquake, and do not call 911 unless you have an emergency.

With phone lines jammed, Sean Mellody, 36, who wants to start a brewing company, shared his pain by tweeting out photos of minor damage to his Queen Village apartment: fallen bricks and cracks in a stairway.

"It was pretty funny to see how I couldn't call home to my family in the suburbs because the cellphones weren't working, but I was getting tweets and Facebook updates just fine," he said.

Anna Martin, who does not typically use social media while at her job with Jefferson Health System in Center City, became her office's information source as her boss looked over her shoulder at her tweets. As coworkers wondered how they would get home, she found eyewitnesses from platforms on SEPTA and PATCO.

"I said, 'See, this is why this is good, because this is going to give you an immediate answer,' " she said.

Megan Wendell, the founder and president of Canary Promotion, a public relations firm, had evacuated with her staff from their Glenside office, but checked Twitter as soon as she got back inside.

Usually, she would wait for word from a news organization before believing what she read on Twitter, she said. But "when your entire Twitter feed is populated by tweets about the same thing," she said, "I obviously know something real has happened."

Contact Daniel Victor at 215-854-2499, dvictor@philly.com,

or @bydanielvictor on Twitter.

Inquirer staff writer Carolyn Davis contributed to this article.