it basically a heavy mass with a particular anisotropy
it absorbs a lot of force in all directions but especially up and down
the thing is this doesn't address the problem that your things in between need to tolerate maybe as much as 100m of immersion and there needs to be a warning system that alerts the dwellers to enter and seal up for this case
as i see it, this is more practical with a tunnel burrowed into solid volcanic rock, at a high altitude, where you don't have to adapt to anything but merely need to breathe for a few weeks while everything is locked down
that's basically the countermeasure i see as most effective, unless you have gravity control and then all bets are off, a lot of things change in their difficulty because you can wrap a space in zero mass