- Ground-motion model is:
where Y is in m∕s2, a = -1.817, b = 0.460, c = -1.428, d = 0.271 and σ = 0.417.
- Use 3 site classes in final model:
s = -1
- Negative residuals from first regression
s = 0
- Zero residuals from first regression
s = 1
- Positive residuals from first regression
Originally use 4 geological units from a macro-zoning for correction of observations to rock:
- Quaternary: very soft soils and alluvium gravel deposits (V s,30 ≤ 360m∕s
- Volcanic: quaternary-tertiary age (360 ≤ V s,30 ≤ 1000m∕s)
- Tertiary: sediments, soft rocks and flysch deposit, 360 ≤ V s,30 ≤ 800m∕s
- Mesozoic: carbonate platform succession, V s,30 > 800m∕s
- Use data from 21 stations of Irpinia Seismic Network, a high dynamic-range, dense, seismographic network
(co-located Geotech S-13J and CMG-5T instruments or a Trillium sensor), from 09/2005 onwards.
- Develop for use in ShakeMaps for small earthquakes.
- Exclude earthquakes from outside area of interest (120 × 120km2) and events with ML < 1.5.
- De-trend and band-pass filter (0.075–20Hz, 4-pole Butterworth) records. Retain records with signal-to-noise
ratio > 5 and where PGA occurs during 5–95% Arias-intensity interval.
- Reasonably uniform distribution w.r.t. M and R, although only one event with ML > 2.9.
- Use three-step approach. Firstly adjust PGAs to rock based on geological classification. Next derive model
using these adjusted PGAs. Examine residuals for each station and perform a Z-test with 5% significant
level to find sites with mean residuals significantly different from zero. Finally add site term to account
for these average differences.
- Test inclusion of quadratic-magnitude term but find that not significantly different from zero.
- Test inclusion of anelastic attenuation term but find that not significantly different from zero.
- Find that the inclusion of the site term d reduces σ and that this reduction is significant by using the
Akaike Information Criterion.
- Compare observed and predicted (grouped by magnitude ranges) PGAs by distance and via residual plots
and find good match.