I heard a crick-crack sound from an outer wall and window, and felt the sofa shake a little bit, like a big truck had just pulled down the alley, fast.
"Did you feel that?" I asked D.
"Feel what?" she said. I decided it had probably just been somebody moving furniture downstairs, or dropping a box, or something.
A few minutes later, beckyb called, and I mentioned what I had observed. She reminded me that there are professionals for this task.
Turns out it really did happen. (here's a plot, there at 02:48 UTC).
[Update Monday: that makes this quake slightly less powerful than the Korean artificial quake.]