No one's really sure what the initial explosion-sound was, but the aftershock was the Twitters exploding with discussion of this #pdxboom! Conspiracy theories! Jokes about aliens! Triangulation!
I live right in the middle of the boom epicenter and I didn't hear anything. Looks like a lot of my neighbors heard it, though. Sigh. I wish I talked to my neighbors somewhere other than on the internet. If I wasn't so busy blogging on a Sunday night, I would throw a #pdxboom block party. And maybe if it wasn't raining.