Exclude records from Ambraseys et al. (2000) from non-free-field stations or those inside a building on
the third floor or higher.
Exclude records from Ambraseys et al. (2000) from stations with unknown or very soft soil site conditions.
Processing procedure of records from Ambraseys et al. (2000) is: baseline correct uncorrected record,
re-sample record to 0.01s time-step and bandpass filtered using a elliptical filter with cut-offs of 0.25 and
25Hz because most instruments were SMA-1s with natural frequency of 25Hz and damping of 60%. No
instrument correction was applied because instrument characteristics are not known.
Only use US records from earthquakes with M > 6.
Use the already corrected records from USGS and CDMG.
Most data from rock sites is from earthquakes with M < 6.
49.7% of data is from Italy and 16.9% is from USA. All other countries contribute less than 10% each.
Use hypocentral distance because believe it accounts for both point and extended sources.
Use uniformly calculated Ms for data from Ambraseys et al. (2000) and Mw for data from W. USA,
which believe is equivalent for Ms for Mw> 6.
Coefficients only reported for horizontal spectral acceleration for 5% damping.
Note that recent data, e.g. Chi-Chi, shows saturation of ground motions at short distances but data used
only contains a few records at close distances so data not sufficient to model such phenomenon.
Obtain positive b(f) coefficients for periods > 1s which believe is due to low frequency noise and surface
Believe that small difference between estimated rock and alluvium motions could be due to incorrect site
classification at some stations.
Repeat regression using a randomly selected half of the data. Find very small differences between predicted
ground motions using half or complete data set so believe equation is stable.
Repeat regression excluding data from W. USA and find very small differences between predicted ground
motions so believe equation is not influenced by data from W. USA.
Repeat regression using Mw rather than Ms if available and find that predicted ground motions are
different but that the predictions using Ms are higher than those using Mw so note that equation using
Ms is conservative hence it is useful in a nuclear safety assessment.
Repeat regression using rrup rather than rhypo and find that predicted ground motions using rhypo are
higher than when rrup is used because using rhypo places source further from source of energy.
Plot residuals for 0.03 and 2s and find not systematic bias in residuals.