Ground-motion model (vertical component) is:
Hard rock: primarily Cretaceous and older sedimentary deposits, metamorphic rock, crystalline rock and hard volcanic deposits (e.g. basalt).
Soft rock: primarily Tertiary sedimentary deposits and soft volcanic deposits (e.g. ash deposits).
Alluvium or firm soil: firm or stiff Quaternary deposits with depths greater than 10m.
Also includes sediment depth (D) as a variable.