I would probably get in touch with a foundation company. If the soil is loose and there are no concrete pilings to support it, or if there are and  they have shifted, it could be a potentially dangerous situation.
Thanks, Randy, and I agree that this could be dangerous.
I've remodeled (repaired? rebuilt?) 3 houses in my life (this is my 4th), but I've never had to deal with this kind of thing before, so I'm really at a loss.