Subsidence is a downward movement of the ground surface over a rather large area due to the irreversible compaction of subsurface soil layers, primarily sand and clay. It's usual cause is subterranean withdrawal of water, oil, or gas. Since it occurs in a large area and at a slow rate, it's effect is long term. Most all homes experience settlement within the first few years after construction. In most cases it is not significant and is in fact quite normal.
Most cracks develop in the foundation walls, slab, masonry veneer, ceiling, or walls.
In severe cases there may be plumbing lines or mechanical equipment failure m or damage. Cracks are generally considered to be of a structural nature when they approach or exceed one quarter inch in width. This is especially true if they only occur seasonally. Slabs Settlement is more noticeable and of greater consequence when it develops in a home with a concrete slab and masonry construction. The engineering design of a slab allows for movement to a limited degree.