A lot of sound can be absorbed by just introducing mass, e.g. a full bookshelf. Shelves need bracing for earthquakes, but if you think of "library quiet", a lot of that is created by how the space is filled, not because people actually behave differently in a library.
Ground vibration also needs mass to dampen, and it's harder to solve without expensive treatments since it ultimately depends on placement relative to loadbearing elements - jumping up and down on a structural beam will be overall less noisy than the flooring in between.
That said, you can lower the frequency by borrowing the techniques of weightlifting platforms: alternating layers of a dense rebond foam and wood.
Ground vibration also needs mass to dampen, and it's harder to solve without expensive treatments since it ultimately depends on placement relative to loadbearing elements - jumping up and down on a structural beam will be overall less noisy than the flooring in between.
That said, you can lower the frequency by borrowing the techniques of weightlifting platforms: alternating layers of a dense rebond foam and wood.