where A is in cm∕s2, a1 = 1.23 (for hard sites), a1 = 1.41 (for soft sites), a2 = 0.385 and a3 = -0.00255 (σ is not given).
Ground-motion model is (for subduction zone earthquakes):
where A is in cm∕s2, b1 = 2.08 (for hard sites), b1 = 2.32 (for soft sites), b2 = 0.35 and b3 = -0.0025 (σ is not given).
Categories 1 and 2 are combined into a hard (H) class and 3 and 4 are combined into a soft (S) class. This boundary established using field evidence at a shear-wave velocity of 400m∕s and at an SPT N count of 60.