Answer:
Sunken relief
Step-by-step explanation:
Relief is a technique of sculpturing in which elements are on the solid background, unattached from it, while in-the-round sculptures are completely three-dimensional and unattached.
When we see the west portal on the Cathedral of St Lazare, we see it is a relief done in the round and attached to the wall behind it.
We can see that it is exactly sunken relief as it is done in the low relief technique, with the sunken area, which means elements do not rise above the original level of the flat surface,