Seismic zonation and earthqueke damage prediction for İstanbul

ABSTRACTIn this study, seismic microzonation maps of Old Istanbul (Eminönü and Fatih Provinces) areprepared in terms of local site effects. Seismic microzonation studies generally involve threestages: the assessment of regional seismicity , identification of geologic structure and faultfeatures, and determination of local geotechnical conditions. The geotechnical local siteeffects are generally evaluated with respect to soil amplification, landslide hazard andliquefaction potential.The seismicity of the region is determined for the probabilities of exceedance of 10% and40% in 50 years with a probabilistic approach, utilizing the studies performed within thescope of GSHAP (1999) project and by using the computer code SEISRISK III (Bender vd.,1987).For the simulation of earthquake motions, a computer code TARSCTHS (Papageorgiou, A.vd., 2000) which is capable of producing spectrum compatible earthquake time histories isutilized. The detailed geology and the fault maps, and geological sections of the study area areprepared utilizing the data from 125 soil borings, geological observations and topographicalfeatures. The study area is divided into 250m*250m cells and representative soil profiles aredefined for each cell based on the geology map and cross sections.The one dimensional behavior of soil layers under earthquake loading is analysed using thecomputer code EERA (Bardet, J.P et.al., 2000) which is based on the propagation of waves ina viscoelastic halfspace, and the earthquake characteristics at the ground surface are weredetermined for each cell. The soil amplification values for each cell are also computed fromequivalent shear wave velocity using the empirical relationship proposed by Midorikawa(1987). The landslide hazard of the region is evaluated using the computer code KoeriSlopeV1.0 (Fahjan, Y.M. vd., 2003) which based on the slope stability analysis method proposedby Siyahi ve Ansal (1993). The liquefaction hazard of the region is assessed based onmodified simplified procedure recommended by Seed et. al. (1984, 1985). The results ofanalysis are processed utilizing GIS techniques in order to produce microzonation maps interms of ground shaking intensity, liquefaction potential and landslide hazard. Themicrozonation maps produced are compared with the damages that took place in the studyarea during the past earthquakes. Generally, the damages that occured during the pastearthquakes are observed to be compatible with the ground shaking maps, and it is alsoconcluded that in some regions liquefaction effects, might have contributed to the damagelevel, whereas no correlation could be established between landslide hazard and earthquakedamage.Keywords: Seismic microzonation, probabilistic earthquake hazard, earthquake simulation,dynamic site response analysis, soil amplification, liquefaction, landslide, geographicinformation systems