The runner in the photo was Bill Iffrig, a 78-year-old retired mason worker resident of Lake Stevens, Wash., according to The Herald of Everett, Wash.
"It was only ... feet away from me," Iffrig said of the explosion. "It was really loud."
Iffrig only received a scrape on his knee from the fall and said that a marathon official helped him cross the finish line.
"I ended up second in my division," he said. "After you've run 26 miles you're not going to stop there."
You can see Iffrig's fall in the following Vine video circulated widely after the blast: