I posted the same question. We live at the corner of 16th and Michigan. Our place was hot the time so we had the misfortune of having our slider open when it happened. I had to peel myself off the ceiling. I definately got the impression that it came from the vicinity of Cermak and Wabash.
I live at 16th and State, and the noise scared the hell out of me as well. I went out on to the terrace, and saw a few people running from the vacinity of 16th and Wabash. About 5 minutes later, there were several police SUVs parked right next to the Firestone, and several K-9 officers were heading into the alley under the el tracks with flashlights heading south with their dogs. There was no smoke or fire to be seen, and this morning, I walked past the area and didn't see any broken glass, fire damage, or anything suspicious. I'm curious like everyone else, what the hell happened? If it had anything to do with the gas or electric, we would have been notified immediately, and I agree, it literally shook the whole house.
There was a large cloud of smoke that dissipated rather quickly. I immediately looked out the window and saw it. If cops were checking out the L at 16th St., that makes sense. It felt close. If a transformer blew on the L tracks, that would explain it.