Does the responsibility for the expense of repairing the cracks that appeared in the entrance to the building's basement after the recent earthquakes fall upon the one who built the fourth floor, or should the repair costs be divided among all residents of the building?

It cannot be definitively stated that the cracks are caused by the construction of the fourth floor, as the possibility of them being caused by the earthquake exists. Assuming they resulted from the construction, the construction was authorized and licensed. Authorization for the action negates liability, as what arises from an authorized act is not guaranteed. Therefore, the builder of the fourth floor is not solely responsible for repairing these cracks.