Geoscience Reference
In-Depth Information
Microzonationstudieswerecarriedoutforfivemunicipalitieslocatedindifferentpartsof
the Marmara Region, Turkey. Depending on the availability of geological, geophysical,
andgeotechnical datatheinvestigatedareasweredividedintototalof819cellsbyagrid
system composed of 500m
×
500m or 250m
×
250m (Erdik et al., 2005; Ansal et al.,
2006b).
Three real acceleration time histories compatible with the earthquake hazard assessment
intermsofprobablemagnitude,distance,andfaultmechanismwereselectedastheinput
rock outcrop motion (Ansal et al., 2006b). The input acceleration time histories were
scaled for each cell with respect to the peak accelerations obtained from earthquake
hazardstudy(Erdiketal.,2005).Thethreescaledaccelerationtimehistoriesforeachcell
wereusedasinputmotionforsiteresponseanalysesusingShake91(IdrissandSun,1992)
andtheaverageofthePGAsandaccelerationresponsespectraatthegroundsurfacewere
determined for each cell toobtain thenecessary parameters for microzonation.
Thegroundshakingintensitymappresentstheestimatedrelativeshakingintensitylevels
based on the combination of two parameters. The peak spectral accelerations (at 0.2s)
calculated from Borcherdt (1994) using equivalent (average) shear wave velocities for
the top 30m were adopted as one of the microzonation parameters. The second para-
meter used was the average spectral accelerations calculated between the 0.1s and 1s
periods using the average acceleration spectra determined from the results of the three
siteresponseanalysesconductedforeachcell.Themicrozonationwithrespecttoground
shaking intensitywas established with respect tothese twoparameters.
The approach adopted in the assessment of the calculated microzonation maps involves
the division of the area into three zones as A, B, and C (Ansal et al., 2004a, b). Since the
site characterisations, as well as all the analysis performed, require various approxima-
tions and some assumptions, it was preferred not to present the numerical values for any
parameter.Inallcases,thevariationsofthecalculatedparametersareconsideredforeach
study area separately and their frequency distributions were calculated. Thus the zone C
shows the most unsuitable 33 percentile (e.g. high spectral accelerations or high spectral
amplification), zone B the medium 34 percentile, and zone A shows the most favourable
33 percentile (e.g. low spectral accelerations or low spectral amplifications). Thus the
final microzonation map is a relative map defined in terms of three zones independent of
theabsolutevaluesofthegroundshakingintensityasshownforBandırmainFigure4.8.
4.2. MICROZONATION WITHRESPECT TOLIQUEFACTION SUSCEPTIBILITY
Liquefaction of soil layers has been a major cause of damage to soil structures, lifeline
facilities, and building foundations during the past earthquakes. The approach that has
gained wide acceptance within the framework of urban planning is to establish micro-
zonation maps with respect to liquefaction susceptibility to mitigate possible earthquake
damage related to liquefaction (Kavazanjian et al., 1985; Todorovska, 1998; Ansal and
Tonuk, 2005).
