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Fig. 18.10. Peak values of shear strainand thecorresponding longitudinal (horizontal)
strainat 3m(left)and 15m(right)depth obtained by 2D numerical simulations of two
geological cross-sections inThessaloniki, subject toin-plane vertical incidence of
S-waves. A M6.5earthquake scenario was considered
groundstrainevaluationandpipelineresponse,atleastasafirstapproximationatshallow
depths
(<
5m
)
.
As a second drawback of the (b) approach, 1D numerical simulations neglect the effects
of lateral variation of soil properties and the onset of surface waves.
PGSs
close to the
surface deduced from 1D analyses are typically smaller than the
PGSa
provided by 2D
simulations. An explanation of this result lies in the fact that the 2D results are mostly
affectedbylaterallyinducedsurfacewaves,sincetheygenerallyrefertogeologicalcross-
sections with important lateral variations of soil properties.
Whenhazardmapsintermsof
PGA
,
PGV
,or
PGS
areavailable,thentheriskassessment
of pipeline systems and networks is carried out using appropriate empirical and semi-
empirical vulnerability or fragility expressions of expected damages (often in terms of
Repair Ratio per kilometer
RR
/km) with the hazard parameters; usually with the peak
ground velocities (eq. 18.6 after O'Rourke and Ayala, 1993) and more recently with the
peak ground strains (eq. 18.7 after O'Rourke and Deyoe, 2004). Further information on
the seismic risk assessment of lifelines may be found in ALA (2001a,b), NIBS (2004),
O'Rourke and Liu (1999), and Pitilakiset al. (2004).
2
.
25
RR
=
0
.
0001
·
(
PGV
)
(
PGV
incm
/
s
)
(18.6)
0
.
89
RR
=
513
·
(
PGS
)
(18.7)
The methodology applied herein is summarized in Pitilakis et al. (2004). It comprises
two main branches; the evaluation of the spatial variability of ground motion for dif-
ferent seismic scenarios and the description of the lifeline network under consideration
(geometry,materials,typology,classification).Foreachtypologyaspecificfragilitycurve
is proposed. Then, through the combination of the appropriate fragility curves for each
