Seeking the name of an animated sci-fi film about a world mined to the point of collapse

I saw an animated film, perhaps a short, about a planet with two levels and two classes. The surface level was enjoyed by a leisure class bent on using as much natural resource as possible. The sub-level was inhabited by miners who built elaborate systems of reinforcement to keep the planet's crust from collapsing into the mined out core area. I seem to remember warnings sent to the surface class, but it took disaster to jar them into stopping their over-consumption. It ended with a "we stopped just in time" feel.