Oil and water are usually in layers so their extraction causes uniform settlement. In unconfined cases, they easily flow to the extraction point without leaving hollow vacuum. But in case of shale gas which is encased in shale rocks, fracturing at a point will allow the gas at that point to flow out leaving hollow rock casing. That's how I imagine it.
But as you said we should not allow ourselves suffer pre-traumatic stresses.
All of this scare stories sounds a bit like Pre-traumatic stress disorder as suffered by Israelis.
We have all heard post traumatic stress disorder where people become insane due to something that happened in the past. Israelis suffer from pre traumatic stress disorder, they all go crazy because they make something up that they say will happen in the future.
So Iran will get nuclear, and kill us all, Muslims will unite and kill us all, that Palestinian baby might one day pick up a stone and kill us all!