[jomama45]

I'd be willing to bet that it's a control or construction joint, OR, if it's a basement, the floor is poured less than 2" thick over the footing.

 

[jomama45]

The part of concrete directly along the wall is your foundation wall. They used the wall itself as the pour stop for the floor.

I agree with this part, it's simply a construction joint, with the foundation wall/weight bearing curb on the outside, and the interior floor on the inside, obviously poured at separate times.

Poor soil preparation and compaction has caused the slab to settle.

Maybe my eyes or reading comprehension are going, but I have no idea where you keep coming up this this assumption that there's any settlement.......

As said before you can either use self-leveling compound to infill or remove and replace the slab making sure to prep the sub-base proper the second time around.

If there is a crawl space below this and the crack has a significant vertical change, then call a structural engineer to review for potential structural defficiencies. If there is a cral space and the crack has no vertical change then is from the floor deflection fighting against the rigid wall and causing a crack at the fulcrum point.

I'd be willing to bet that it's simply a slab on grade. I can see zero benefit from a suspended concrete floor over a crawlspace. No reason to spend all of that money w/o adding usable square footage to the building.