Before the Left Coasters give a raspberry to a 4.0, let it be known that the plate tectonics are radically different between the west, the middle, and the east.
On the west, the plate is like the crust of an apple pie, and it takes a lot more force to cause things to travel and be felt. The plates on the east and middle of the continent is more like the surface of a church bell. A hit from underground, even a small one, travels and is felt much more easily, so a 4.0 is indeed a big thing.
I’m guessing it was very deep.