An Assessment of the relationship between the local site effects and the distribution of damage in the city of Yalova (Turkey) during 17 August 1999 İzmit earthquake

İlhan, Cemal
The relationship between the local site effects and the damage distribution at the City Centre of Yalova after 1999 İzmit earthquake is investigated. The spatial distribution of building damage is presented by compiling the damage statistics reported after the event. It is observed that structural damage at the coastal areas and the ridges were limited. The most severe damage, however, was observed on Hacımehmet Basin and on the west side of Bağlarbaşı Quarter. Peak ground acceleration during the earthquake is estimated by available ground motion estimation equations. Then, liquefaction evaluations are conducted for the available borehole data. It is concluded that, some deposits of the coastal areas with variable thickness have liquefaction potential. Finally, liquefaction potential map of the site in terms of liquefiable thickness is prepared. It is shown that the frequency of collapsed buildings near the boreholes with a liquefiable layer thicker than 2 m is limited. The relationship between the spatial distribution of collapsed buildings and the local site effects are investigated by one-dimensional non-linear site-response analyses, including response of liquefying layers. Idealized profiles are analysed with five selected and scaled ground motion records. The computed spectral accelerations and spectral amplification ratios are presented. One-dimensional site-response simulations showed that the liquefaction can reduce the spectral amplitudes by a factor about 2.5 in the range of periods from 0.3 s to 0.4 s. This result is consistent with the observed building damage in the City. However, intensity of damage at Hacımehmet Plain cannot be explained with one-dimensional analyses. It is considered that two-dimensional response of the basin might have a prevalent contribution to the seismic demand in this area.