Strong ground motion estimation in the Sea of Marmara region (Turkey) based on a scenario earthquake

We perform a broadband frequency bedrock strong ground motion simulation in the Marmara Sea region (Turkey), based on several fault rupture scenarios and a source asperity model. The technique combines a deterministic simulation of seismic wave propagation at low frequencies with a semi-stochastic procedure for the high frequencies. To model the high frequencies, we applied a frequency-dependent radiation pattern model, which efficiently removes the effective dependence of the pattern coefficient on the azimuth and take-off angle as the frequency increases. The earthquake scenarios considered consist of the rupture of the closest segments of the North Anatolian Fault System to the city of Istanbul. Our scenario earthquakes involve the rupture of the entire North Anatolian Fault beneath the Sea of Marmara, namely the combined rupture of the Central Marmara Fault and North Boundary Fault segments. We defined three fault rupture scenarios based on the location of the hypocenter, selecting a preferred hypocentral location near a fault bend for each case. We analysed the effect of location of the asperity, within the Central Marmara Fault, on the subsequent ground motion, as well as the influence of anelasticity on the high-frequency attenuation characteristics. The fault and asperity parameters for each scenario were determined from empirical scalings and from results of kinematic and dynamic models of fault rupture. We calculated the resulting time series and spectra for ground motion at Istanbul and evaluated the sensitivity of the predictions to choice of model parameters. The location of the hypocenter is thus shown to be a critical parameter for determining the worst scenario earthquake at Istanbul. We also found that anelasticity has a significant effect on the regional attenuation of peak ground accelerations. Our simulated ground motions result in large values of acceleration response spectra at long periods, which could be critical for building damage at Istanbul during an actual earthquake. (C) 2004 Elsevier B.V. All rights reserved.