After such outstanding advise on Earthquake Proofing I'm back for more :)
A plumber I'm working with got a little over-zealous when relocated an ABS pipe stack. By cutting too large of a hole in a joist, he's undoubtedly created a code violation, but I'm more concerned that he's compromised the structural integrity of the joists. I'm especially sensitive as my side-door appears to be sticking, when it wasn't before - which is always a bad sign.
There are two photos of the affected area below. I'll try to describe it as best I can...
The plumber cut a 4 1/4" sloppy hole in a 9" joist. The hole is cut about 3/4" from the bottom edge of the joist. The joist had a bad notch already to begin with close to where it rests on the sill plate and in addition - it appears to be sharing the load of the joist next to it which has been previously cut short and shored into its neighbouring joists.
These are old 1914 25 foot long 9" joists.
So assuming the answer is "Yes". How do I fix it?