- Ground-motion model is:
where PGA is in g, c1 = -0.45 ± 0.44, c2 = 0.85 ± 0.09, c3 = -2.39 ± 0.20 and σ = 0.27 for Italy with
station correction and c1 = -0.49±0.38, c2 = 0.86±0.08, c3 = -2.41±0.16 and σ = 0.38 for Italy without
station correction. Sk is correction term for kth station and δkj is Kroneker delta and Ns is number of
stations in a geographical cluster. Also provides coefficients for different zones but these are not reported
- Uses individual site terms for each station. Data from 137 different stations.
- Investigates theoretical improvement of GMPEs for ShakeMap purposes in Italy, obtainable by accounting
for regional dependencies and site effects. Notes that presented GMPEs are explorative tools rather than
proposals for ShakeMap implementation because of limited data and narrow magnitude range.
- Uses data from INGV stations from between December 2005 and July 2008. Stations give homogeneous
coverage in central and southern Italy and eastern Sicily but more sparse elsewhere and not existent in
- To exclude possible outliers, performs preliminary regression on all data and removes those records with
absolute normalised standard deviations greater than three. Also excludes data from stations that have
recored only one earthquake.
- Data distribution roughly uniform w.r.t. magnitude and distance.
- Tries using rhypo but finds a slightly worse fit (σ = 0.39 rather than σ = 0.38), which relates to poor
estimates of focal depths for some earthquakes (even though theoretically rhypo should be better since it
includes more information).
- Considers various partitions of available stations into different geographical zones using Delaunay
triangulation. Derive a GMPE for each zone with station correction terms. Applies a genetic algorithm
to minimise the standard deviation, based on the Bayesian information criterion, over the set of possible
partitions. Note that this approach cannot recognise regionalised site effects. Also this method uses some
data from earthquakes occurring outside the zone where the station is located. Notes that considering
these complexities is not possible with current data but that most earthquakes occur in the same zone as
the station. Finds that the optimal zonation has four zones.
- Investigates source and focal depth characteristics of different zones to understand the possible causes of
regional variations. Concludes that observed differences are attributable to crustal structure and anelastic
- Computes GMPEs for the six regions used in ShakeMap implementation.
- Computes GMPEs for all of Italy after correction for site amplification modelled by V s,30-based
amplification factors of Borcherdt (1994), used by ShakeMap. Find σ is unchanged. Also regress using site
classes based on V s,30s estimated from geology.
- Concludes that site effects contribute about 30% of overall standard deviation and that regional differences
contribute only 4%.
- Find that station correction terms are weakly correlated to V s,30-based amplification factors of
Borcherdt (1994) used in ShakeMap to model site effects.