I can't answer your question, but I can tell you about small quakes, the only kind we get in the DFW area. There have been quite a few 2s and 3s that I never noticed. I did notice about a 3.1 once. It felt like someone had slammed a heavy door a few rooms away, just a tiny jolt through the floor. The bigger impact was the sound, which was like someone dropping a heavy rock onto pavement outside, which is what I'd thought had happened until I realized I barely felt something. It was late at night and quiet. If I'd been watching television on the couch I could have easily missed the jolt and sound.
I was in about a 3.4, which I barely noticed as a light shake for a second or two.
My biggest one was a 4.0, which shook for a few seconds and was definitely noticeable. This one made a bit of a rumbling sound.