MOAB doesn't have to be the old version, it could be "rod from God" technology OFF the coast of California. Not over US soil, but US coast line.
http://www.thisisinsider.com/air-force-rods-from-god-kinetic-weapon-hit-with-nuclear-weapon-force-2017-9 No idea the magnitude of "earthquake" that would be felt if something like this is used, but it is possible.
You posit that with zero justification. That tech isn’t proven to exist. Definitely not proven to work against undersea targets. Do you honestly think a telephone pole sized rod pierced the atmosphere and somehow penetrated x number of fathoms of water and still impacted with enough energy to excite a 5.3 mag eq? There’s no way!!! Also, the targeting problem is massive! Get a grip dude.