- Ground-motion model is:
where y is in g, for 5 ≤M < 6 a = 1.2, b = 0.066, c = 0.033, d = 23 and standard error for one observation
of 0.06g, for 6 ≤M < 7 a = 1.2, b = 0.044, c = 0.042, d = 25 and standard error for one observation of
0.10g, for 7 ≤M ≤ 7.7 a = 0.24 b = 0.022, c = 0.10, d = 15 and standard error for one observation of
0.05g and for 6 ≤M ≤ 7.7 a = 1.6, b = 0.026, c = -0.19, d = 8.5 and standard error for one observation
- Use data of Joyner and Boore (1981).
- Form of equation chosen to satisfy plausible physical assumptions but near-field behaviour is not
determined from overwhelming contributions of far-field data.
- Apply nonlinear regression on y not on log y to give more weight to near-field values.
- Split data into four magnitude dependent groups: 5 ≤M < 6, 6 ≤M < 7, 7 ≤M ≤ 7.7 and 6 ≤M ≤ 7.7.
- Use form of equation and regression technique of Joyner and Boore (1981), after removing 25 points
from closer than 8km and find very similar coefficients to Joyner and Boore (1981). Conclude from this
experiment and their derived coefficients for the four magnitude groups that using their form of equation
predicted near-field accelerations are not governed by far-field data.
- Find no evidence of systematic increase in PGA near the source as a function of magnitude and that the
large scatter prevents attaching significance to differences in near-field PGA which are predicted using
their attenuation relations for different magnitude ranges.