The Effect of soil nonlinearity on ground motion amplification in Urmia City

Direct observations from past earthquakes، experiences and modeling carried out by researchers، have shown that the ground motion during earthquakes is impacted by a great variety of factors such as specific site-soil behavior، source and path effects. With respect to the subject، the nonlinear behavior of Urmia city’s sediment has been studied in this paper. First the methodology of soil nonlinear response analysis، including the constitutive model and dynamic equation of motion for horizontally layered soils and it’s time domain solution has been investigated. Afterwards، geotechnical properties of underlying soil for Urmia city have been interpreted. Seismic hazard maps of seismic geotechnical bedrock have prepared for 3 hazard levels. One- dimensional ground response analysis has conducted. Synthesized acceleration time histories for analysis according to regional seismic hazard analysis and the maximum ground acceleration and response spectra in ground surface have been calculated and compared with maximum ground acceleration and response spectra of bedrock and then the amplification spectra of the surface was obtained. Finally according to geotechnical information and estimated amplification factors، the Urmia city is divided into five regions and amplification spectrum for each region has been proposed.