Dripping

The headline at SciTech is evocative: Scientists Discover That North America Is “Dripping” Down Into Earth’s Mantle.

Although the dripping is concentrated in one area of the craton, Hua said that the plate appears to be interacting with material from across the entire craton, which covers most of the United States and Canada.

“A very broad range is experiencing some thinning,” Hua said.

The image that comes to mind is water dripping from a faucet, which on the small scale is pretty dramatic, with a lot of shake-up. If you scaled that up, you could imagine a blob pinching off under the continent (e.g. New Madrid) with a resulting big up-bounce afterwards.

(Bigger image here)

But the "drip" is into a medium not much less dense than the dip itself, and the sizes involved suggest a much slower and wider "bounce". A simulation suggests "drips" of order 50km and timescales of order millions of years, not seconds.

Stresses and stress relief might trigger some other fault into action, of course.