4.112 Berge-Thierry et al. (2003)

• Ground-motion model is:

  where c₁(f) is for rock sites and c₂(f) is for alluvium sites.

• Use two site categories based on V _s where V _s is the average shear-wave velocity in top 30m:

  1.

  Rock, V _s > 800m∕s.

  2.

  Alluvium, 300 < V _s < 800m∕s.

  Note that some uncertainty in site classification due to lack of V _s values at many stations.

• Response parameter is spectral acceleration for 5%, 7%, 10% and 20% damping.
• Note that not enough data to derive an equation using only French data so had to use European and US data.
• Use only records from earthquakes with focal depth ≤ 30km so as to be consistent with shallow crustal earthquakes in France.
• Predominately use corrected data from Ambraseys et al. (2000).
• Supplement European data with some data from western USA to improve the magnitude and distance distribution.
• Exclude records from Ambraseys et al. (2000) from earthquakes with M_s < 4.
• Exclude records from Ambraseys et al. (2000) with record lengths < 10s.
• Exclude records from Ambraseys et al. (2000) with poor visual quality.
• 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 M_s for data from Ambraseys et al. (2000) and M_w for data from W. USA, which believe is equivalent for M_s for M_w > 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 waves.
• 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 M_w rather than M_s if available and find that predicted ground motions are different but that the predictions using M_s are higher than those using M_w so note that equation using M_s is conservative hence it is useful in a nuclear safety assessment.
• Repeat regression using r_rup rather than r_hypo and find that predicted ground motions using r_hypo are higher than when r_rup is used because using r_hypo places source further from source of energy.
• Plot residuals for 0.03 and 2s and find not systematic bias in residuals.