When the ground began to vibrate in Fukushima, Japan on March 11, Ryan McDonald thought it was just a “normal earthquake.” But the fear in his voice as the vibrations escalated was palpable. In video uploaded to CNN’s iReport, McDonald screams, “Oh my God, the building’s going to fall!” as he frantically shifts the camera’s view into what looks like a garage and then out into the street.

McDonald’s video is one of the hundreds uploaded onto CNN’s iReport focused on the deadly Japan earthquake that has killed thousands and disrupted the lives of millions. Not long after he submitted the video he was invited onto a live CNN broadcast where he used Skype and a computer headset to field an interview. “I’ve been in Japan for nine years,” he told the CNN host. “I’m an English teacher here… In those nine years I’ve never been concerned, or worried, or scared about an earthquake. But with this I was truly terrified.”

In the week after the earthquake, CNN invited several other iReporters on air to recount their own firsthand experiences of the disaster, a strategy that allowed the network to enrich its reporting on the region as other news organizations were struggling to get their own reporters on the ground. The New York Times reported last week that CNN — which has often drawn last place ratings against its cable news competitors — shot up to the ratings lead in the earthquake’s aftermath, attracting over 2 million viewers on some nights. Given that a sizable portion of this coverage focused on footage from iReports and interviews with the citizen journalists who recorded them, at least some of CNN’s success can be attributed to its iReport community.

Lila King, iReport’s participation director, told me in a phone interview last week that it’s not uncommon to see a flood of iReports, not only in the immediate aftermath of a major news event but in the weeks following, as well. “There’s the first wave of iReports,” she said. “An event happens and people post photos or videos immediately — the immediate damage and after-effects. And then once CNN begins covering the story, both through television and online, then there’s a second wave of iReports.”

This second wave, she explained, comes from viewers at home who watch the iReport interviews and are inspired to produce their own. Often the videos in this second wave are more diverse; they can include both video diaries of people speaking into the camera offering their opinions and more well-edited videos exploring the indirect implications of a major news event. With Japan, the first wave of iReports originated in the disaster area and then moved on to Tokyo before migrating to the California coast. There were videos of waves crashing into the US shore and of tourists huddling on the ground in a Honolulu hotel, fearing the possibility of a tsunami.

So how does the collaboration between the main network and the iReport team take place? King said that her team — made up of about nine people — sits right in the middle of the CNN newsroom. “They’re like 20 yards from the person who’s running the homepage, so if something happens, you’re within shouting distance,” she said. “It’s just a constant communication like in the middle of any newsroom. With something like this, what typically happens is that an event takes place and then iReport gears up to go build a page to house all the incoming iReports so we can set it up for our television colleagues, and then on the homepage of CNN.com. Then there’s a lot of shouting across the room and telephone calls and daily emails to deal with the iReports that still have to be vetted.”

What makes iReport stand out from other citizen journalism sites, King said, is the fact that CNN makes an attempt to verify as many of its submissions as possible. An iReport producer will often speak directly to an iReporter, and it’s during these conversations that the producer may bring up the possibility of the iReporter going live on the air to tell his or her side of the story. “When you talk to someone, you get a sense of what their story is, and how they tell it,” she said. “Obviously that can be very important for television. We will just ask people, ‘Would you be willing or interested in talking to someone live on the air?’ In general — not just for this story, but for iReport overall — probably half the people we ask that question to are really excited and the other half decline it outright. It can be a very tough thing to do, doing a live interview on television. When people are willing, we ask them for their Skype handle or iChat or whatever it is that they have, and then we patch them through to the newsroom.”

Since its launch in 2006, 753,000 people have registered iReporter accounts, and a CNN spokeswoman told me that the network sees an average of 2.1 million unique visitors to the iReport section of the site. So far, 799,959 videos and images have been uploaded.

I asked King whether most the uploads deal with major news events like the Japan earthquake.

“When iReport started, we all expected spikes around breaking news reports, and we’ve certainly seen that, especially in this case,” she replied. “But one of the things that surprised me the most is that there is a whole other world in iReport that’s much more focused on feature storytelling through local personal stories.”

Some of those personal stories will be about what it’s like to live through an earthquake, while others are simply showing off a user’s new iPad. The goal of King and her colleagues is to push the most newsworthy of those stories into the spotlight, whether through the homepage of CNN.com or a feature with Wolf Blitzer on his show. Not only does CNN employ more news journalists than its fellow cable news competitors, but it also has its own personal army of citizen journalists, showcasing the voices of some who didn’t even know they had one.