Geoscience Reference
In-Depth Information
elementofdifferenttypologyandtheestimatedseismicactions(i.e.groundmotionpara-
meters like
PGV
and
PGS
), we evaluate the number, the type (i.e. leaks, breaks) and the
location of the damages. There are three issues of great importance and equally large
difficultyintheriskassessmentoflifelinesystemsasdescribedabove.Thefirstone,dis-
cussedalreadyinpreviousparagraphs,isrelatedtotheaccuracyofestimatingthespatial
variability, and the characteristics of ground motion (amplitudes, frequency content) in a
specific site, for example a city. Local surface geology, 2D and 3D geometry of alluvial
depositsandbasins,soilcharacteristics,seismotectonicfeatures,andmethodsofanalysis
are among the basic parameters which play a crucial role in the accuracy of estimated
groundmotions.Theapplicationwhichfollowswillattempttoillustratefurtherthediffi-
cultiesandthecomplexityoftheproblemoftheselectionofthegroundmotionparameter
when itisto be used for theseismicriskassessment of spatiallyextended systems.
The second problem is the inherent difficulty to know the exact geometry and typology
of the lifeline systems, comprising often hundred of kilometers of pipes, constructed in
different periods with different materials and procedures. The third major problem is
the empirical nature of the fragility curves and the lack of many different well docu-
mented studies for different earthquakes and systems around the world. While in Japan
and America there are some good data, in Europe there is a tremendous penury of infor-
mation and usually the available data are not well documented. Among the few excep-
tionstherecentLefkasearthquake(
M
6.5,2003)intheIonianislandsinGreece,which
affectedseriouslythewatersystemsofthecity(Alexoudi,2005).Thisisthemainreason
of moderate credibility when using available fragility curves without proper validation
andimprovement.Inthissenseitisveryimportanttodeveloptheoreticalfragilitycurves
applying sophisticated numerical models.
w
4. Application examples
Thefirstexamplepresentedanddiscussedhereinconcernstheseismicriskassessmentof
the main water system of Duzce (Turkey) seriously damaged during the devastating
M
w
7.1earthquakein1999,alreadyaffectedbytheprevious
M
7.4Kocaeli1999earthquake.
As liquefaction phenomena have not been observed in Duzce, damages are due only to
groundshaking.Thereporteddamages,withoutanydistinctionbetweenbreaksandleaks,
aresummarizedinFigure18.11(Tromans,2004).Thedocumentationispoorandthedata
aresummedperdistrict.Moreoverthereisnoreferencetothepercentageandtheintensity
of damages during the previous (only three months before) earthquake of Kocaeli.
w
The full re-examination of the damage reports few years after the earthquake reveals at
least 21 well documented cases, which are described in Figure 18.12 (Pitilakis et al.,
2005).
Duzce is located in the center of a large plain (Figure 18.6). The geotechnical conditions
are characterized by medium rigidity sands and clays with gravels
)
of high thickness. In the center of the city, due to the river crossing, the surface soils
(mainly silty sands) are looser with mean
V
s
of the order of 200-250m/s. The seismic
(
Vs
=
300-450m
/
s
