Some power hammers need a substantial footing some don't. Rating of hammer weight is not the factor that determines this. I can't explain it as well as the Phoenix Power Hammer page does but it has to do with total mass. My tire hammer weight is about 1000# total with an anvil and base plate weight of about 600#, but is only a 35# hammer. I have no special footing but it does sit on a pad made from 2 x 4s laid flat with a 2 x 2 frame to contain the base. It sits on a standard thickness garage floor (residential construction: circa 1975) No ill effect so far.
Phoenix says even their 500# needs no special footing but again it has to do with total mass. Check out this link for better explanation.
Phoenix Forginghammers : What is Cast Iron Fever? It mainly scoffs at cast iron hammers but the important idea is about the anvil mass so read the whole thing.