Seriously, it WILL happen...
Atom interferometer based devices WILL get more compact and cheaper. Imagine watching magma move when you have a network of these devices. The fiber optic method gives you data about the surface from which you can infer what MIGHT be happening below... quantum sensors can allow you to 'see' below the surface more directly.
Perhaps you could map mines roughly from the surface?
I wonder if aquifers and oil deposits have tides...?