where Y is in g, for M > 1.5 using acceleration and velocity records, for horizontal PGA C1= -4.2318,
C2= 1.1962, C3= -0.0651, C4= -1, C5= -0.0019, C6= 0.261, h0= 2.9 and σ = 0.432 and for vertical
PGA C1= -4.1800, C2= 1.0189, C3= -0.0404, C4= -1, C5= -0.0019, C6= 0.163, h0= 2.7 and
σ = 0.415.
Use two site categories:
S = 0
Rock, H: 470 records, V: 395 records.
S = 1
Soil, H: 88 records, V: 83 records.
Note that not most accurate approach but due to lack of site information consider this technique makes
most consistent use of available information.
Select data using these criteria:
Epicentre and recording station must be within the stable continental region boundaries defined
by Johnston et al. (1994) because a) such regions form end of spectrum of regions described by
‘intraplate’ and hence allows differences with interplate regions to be seen, b) they are clearly
delineated regions and c) intraplate oceanic crust is excluded.
Minimum magnitude level M = 1.5.
Use records from dam abutments and downstream free-field sites but excludes records from crests,
slopes, toes, galleries, or basements.
Use records from acceleration and velocity instruments.
Specify no minimum PGA.
Specify no maximum source distance. Do not exclude records from distances greater than shortest
distance to a non-triggered station.
Data from Australia, N.W. Europe, Peninsular India and E. N. America.
Focal depths, 2 ≤ h ≤ 28km.
Most records from M < 4.0.
Visually inspect all records including integrated velocities and displacements, identify and remove traces
dominated by noise, identify and correct transient errors (spikes, ramps, linear sections, back time steps
and clipped peaks), identify scaling errors, identify and remove multiple event records. Linear baseline
correct and elliptically filter with cut-off 0.25 to 0.5Hz (determine frequency by visual inspection of adjusted
record) and 33 to 100Hz (generally pre-determined by Nyquist frequency).
Large proportion of records from velocity time histories which differentiate to acceleration. Test time
domain method (central difference technique) and frequency domain method; find very similar results. Use
time domain method.
Distribution with respect to magnitude did not allow two-stage regression technique.
In many analyses distribution of data with respect to distance did not allow simultaneous determination
of coefficients C4 and C5, for these cases constrain C4 to -1.
Test effect of minimum magnitude cut-off for two cut-offs M = 1.5 and M = 3.5. Find if include data
from M < 3.5 then there is substantial over prediction of amplitudes for d < 10km for large magnitudes
unless include C3 term. C3 effectively accounts for large number of records from small magnitudes and so
predictions using the different magnitude cut-offs are very similar over broad range of M and d.
Try including focal depth, h, explicitly by replacing h0 with h because h0 determined for whole set (which is
dominated by small shocks at shallow depths) may not be appropriate for large earthquakes. Find improved
fit at small distances but it does not result in overall improvement in fit (σ increases); this increase thought
due to large errors in focal depth determination.
Find larger standard deviations than those found in previous studies which note may be due to intrinsic
differences between regional subsets within whole set. Repeat analysis separately for Australia (for
horizontal and vertical), N. America (for horizontal and vertical) and N.W. Europe (horizontal); find
reduced standard deviations (although still large), C5 varies significantly between 3 regions.