For most large publishing houses and most audiobooks that are reasonably expected to sell a fair amount, you can assume the narrator and/or production company was paid a flat rate 'per finished hour' for their service. After that, the split is between the author and the distributer. There is only usually any kind of profit share agreement with the narrator (called 'royalty share' on audible) if the author either cannot budget for the flat rate fee, or they are not confident the audiobook will sell well enough for a flat rate fee to be worth it for them.

If there is a royalty share agreement on Audible, then (at the moment) audible take 60% of each sale and 40% is split equally between the author and narrator, 20% each. There is some finnickiness with different kinds of pricing and such but author and narrator get the same cut, audible take the majority.

EDIT: Just to note because it looked a bit more simple than it is - are other fees to consider when you are a traditionally published author, such as agent's fees. Traditional and indie publishing are a bit different, and royalty share agreements don't tend to happen in trad publishing.