Gaull (1988)

Ground-motion model is: $log PGA = [(a1log R + a2)∕a3](ML - a4)- a5 log R - a6R + a7$
where PGA is in m∕s2, a₁ = 5, a₂ = 3, a₃ = 20, a₄ = 6, a₅ = 0.77, a₆ = 0.0045 and a₇ = 1.2 (σ not given).
Considers three site categories but does not model:
1.
Rock: 6 records
2.
Alluvium: 5 records
3.
Average site: 10 records
Most records from earthquakes with magnitudes about 3 and most from distances below about 20km.
Band pass filter records to get PGA associated with waves with periods between 0.1 and 0.5s because high frequency PGA from uncorrected records not of engineering significance.
Adds 4 near source (5 ≤ R ≤ 10km) records from US, Indian and New Zealand earthquakes with magnitudes between 6.3 and 6.7 to supplement high magnitude range.
Add some PGA points estimated from intensities associated with 14/10/1968 M_L = 6.9 Meckering earthquake in Western Australia.
Plot 6 records from one well recorded event with M_L = 4.5 and fit an attenuation curve of form log PGA = b₁ - b₂ log R - b₃R by eye. Plot PGA of all records with 2 ≤ R ≤ 20km against magnitude, fit an equation by eye. Use these two curves to normalise all PGA values to M_L = 4.5 and R = 5km from which estimates attenuation relation.