where PGA is in g, a1= 0.1548, a2= 0.5442, a3= 8 and a4= 1.002 (σ not given).
All records from aftershocks of 1975 Haicheng earthquake and from 1976 Tangshan earthquake and
Most records from earthquakes with magnitude less than 5.8 and from distances < 30km.
Exclude records with PGA < 0.5m∕s2 to avoid too much contribution from far field.
Due to small number of records simple regression technique justified.
States valid for 4 ≤ M ≤ 6.5 and R ≤ 100km.
Also use 158 records from western N. America to see whether significantly different than N. Chinese data.
Derive equations using both western N. American and N. Chinese data and just western N. American data
and find that predicted PGAs are similar, within uncertainty.
Insufficient data to find physically realistic anelastic term.