If the crack does not extend to the foundation wall, the concrete is not displaced, the crack is discontinued in nature, then its going to be shrinkage.
An earth quake is not going to present that type of crack, in the middle of the room while not extending to the side.
If you have cracking as a result of earthquake…there will be cracks in the foundation as well…not just in the middle of a slab floor where upon the crack doesn’t even extend to the foundation wall.
Looks like they already have the baseboard up…a tell tale sign would be to see if there is spacing between the foundation wall and the slab itself which is directly related to shrinkage and is normal.
If anything, it would be seal for radon purposes…then again, that crack may not present such an issue is 6 mil poly was laid.
Picture 1 doesnt show any clarity…
Picture 2 shows the crack to be fairly straight…which their could be a keyway under same.
Picture 3 is showing approximately up to a 3/32 of a crack without any displacement whatsoever, vertical or horizontal…I use that to rule out any earthquake effects.
Just to be curious…what are you going to say when “calling” this crack (evidently 1 crack) out…“noted one (1) small crack less than 1/4 inch in width with no displacement, in the middle of the room extending approximately 4 - 6 feet however same does not extend to the foundation wall; further evaluation is warranted by a soil and or structural engineer.”
Not to be facetious but if you think its a structural issue (which it seems that some of you do) then calling out anyone besides a soil and or structural engineer will be useless.
Ken made a good point in mentioning expansive soils…here in NC we went through a drought for several years (some say we still are in one in our area)…we then had a short season of extensive rain several years ago…what do you think happened to all the basements and slab homes in the area…talk about insurance claims being filed (and often rejected).
If anything I may make mention of it in the body of my report, simply stating that no displacement was noted, the crack was limited and should be filled…unless you have pictures of crackings in other areas of the house including the foundation, wallboards / drywall, siding, trim caulking pulled loose etc…I would move on, but that’s me.
regards
Jeff
PS. I hope you all didn’t forget Mother’s day…