MONTE CARLO SIMULATIONS OF SOIL AMPLIFICATION FUNCTIONS FOR SITE-SPECIFIC SEISMIC HAZARD ANALYSIS – CASE STUDY: TEHRAN, THE CAPITAL CITY OF IRAN

To design earthquake resistant buildings and structures, strong ground motions’ accelerations and their uncertainties should be estimated. Nevertheless, the effect of soil-profile amplification needs to be evaluated for a complete site-specific seismic hazard estimation. Despite all uncertainties in hazard analyses phases including source, magnitude and attenuation equations, soil profiles are of high deviations in properties and characteristics in a study area. To tackle soil profile uncertainties in the site-specific seismic hazard estimation results, in the present work, a Monte Carlo simulation (MCS) approach has been proposed and examined to evaluate soil amplification function at each soil profile location or borehole. In the proposed approach, shear modulus, damping ratio, soil density and layer thickness are considered as random variables, which follow their corresponding probability distribution functions. The method includes 10,000 times randomising soil layer thicknesses as well as shear modulus reduction models, damping increase models and unit weights for each soil profile. In the present paper, soil amplification functions are achieved utilising SHAKE91 while an in-house subroutine generates a mega-input file for MCS at each soil profile. Furthermore, greater Tehran, the capital city of Iran and one of the most seismically active urban areas in the world, has been considered as a case study for the proposed method. Analysing the soil borehole data received from the governmental authorities, MC simulated mean soil amplification functions as well as the transformed surface uniform hazard spectrum from the bedrock spectrum have been presented respectively, for a borehole among all the database in Tehran area.