where PHA is in g, a = -2.501, b = 0.623, c1= 7.28 and σ = 0.506.
Selects records from deep soil (> 10m). Excludes data from shallow soil (≤ 10m) and rock sites and
those in basements of buildings or associated with large structures, such as dams and buildings taller than
two storeys. Selects records with epicentral distances ≤ 20km for ML< 4.75 and distances ≤ 30km for
ML≥ 4.75 to minimize regional differences in anelastic attenuation and potential biases associated with
nontriggering instruments and unreported PGAs.
Focal depths, H, between 1.8 and 24.3km with mean of 8.5km.
PGAs scaled from either actual or uncorrected accelerograms in order to avoid potential bias due to
Uses weighted nonlinear least squares technique of Campbell (1981).
Tries two other forms of equation: lnPHA= a + bML- 1.0ln[R + c1] + e1H and lnPHA= a + bML-1.0ln[R+c1]+e2lnH for epicentral and hypocentral distance. Allows saturation of PGA for short distances
but finds nonsignificant coefficients, at 90%. Also tries distance decay coefficient other than -1.0 but finds
instability in analysis.
Examines normalised weighted residuals against focal depth, ML and distance. Finds that although
residuals seem to be dependent on focal depth there are probably errors in focal depth estimation for deep
earthquakes in the study so the dependence may not be real. Finds residuals not dependent on magnitude
Uses 171 records (0.9 ≤ R ≤ 28.1km) from 75 earthquakes (2.5 ≤ ML≤ 5.0, 0.7 ≤ H ≤ 24.3km)
excluded from original analysis because they were on shallow soil, rock and/or not free-field, to examine
importance of site geology and building size. Considers difference between PGA from records grouped
according to instrument location, building size, embedment, and site geology and the predicted PGA using
the attenuation equation to find site factors, S. Groups with nonsignificant, at 90%, values of S are grouped
together. Finds two categories: embedded alluvial sites from all building sizes (38 records) and shallow-soil
(depth of soil ≤ 10m) sites (35 records) to have statistically significant site factors.
Performs regression analysis on all records (irrespective of site geology or building size) from Oroville (172
records from 32 earthquakes) and Imperial Valley (71 records from 42 earthquakes) to find individual sites
that have significant influence on prediction of PGA (by using individual site coefficients for each station).
Finds equations predict similar PGA to those predicted by original equation. Finds significant differences
between PGA recorded at different stations in the two regions some related to surface geology but for some
finds no reason.
Uses 27 records (0.2 ≤ R ≤ 25.0km) from 19 earthquakes (2.5 ≤ MbLG≤ 4.8, 0.1 ≤ H ≤ 9km) from
E. N. America to examine whether they are significantly different than those from W. N. America. Finds
residuals significantly, at 99% level, higher than zero and concludes that it is mainly due to site effects
because most are on shallow soils or other site factors influence ground motion. Correcting the recorded
PGAs using site factors the difference in PGA between E. N. America and W. N. America is no longer
significant although notes may not hold for all of E. N. America.