Ground-motion model for rock is:
Use different models to force rock and soil accelerations to same level in near field.
Rock: Consists of at most about a metre of soil over weathered rock, 96 records.
Deep soil: Depth to bedrock is greater than 20m, 284 records.
Shallow soil: Depth to bedrock is less than 20m and a significant velocity contrast may exist within 30m of surface, 96 records.