The high frequency decay parameter, kappa and its variations in distance is evaluated using 114 three component strong motion records from two strong events in Northwestern Iran. We show that in classical method of estimating kappa, the results are very sensitive to the choices of [Formula: see text] (where spectrum starts to fall) and [Formula: see text] (where spectrum reaches the noise floor) and automated procedures for estimating kappa are likely to lead to a biased estimation. For the present database, we found an obvious concavity in dependency of kappa on distance. The kappa values in distance were regressed to a trilinear shape for which the first line has a zero slope. Based on this trilinear shape the zero distance kappa are 0.043 and 0.026 for horizontal and vertical components, respectively.

The goal of this study is to estimate source and path attenuation parameters of recorded earthquakes in Tehran province, Iran so they can be used for strong motion prediction purposes. For this, we have used four well recorded earthquakes recorded on Iran Strong Motion Network (ISMN). Assuming a simple geometric spreading of 1/r we have estimated Q factor for S-wave attenuation by characterizing spectral amplitude decay with distance at discrete frequencies. We propose the form of Q(f)=73f 0.72 for attenuation of S-wave in Tehran province. We show that the proposed attenuation quality factor is in the range of Q factors that have been proposed by the other studies. We have also estimated source parameters, such as seismic moment (M 0), corner frequency (f c) and Brune stress drop (Δσ) for each earthquake. We have fitted Brune source model to the observed spectra of motion by a grid search for least squares. Stress drop for studied earthquakes ranges between 7.7 to 37.1 MPa (77 to 371 bars).

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The main purpose of this study is to predict strong ground motions from future large earthquake for Karaj city, the capital of Alborz province of Iran. This city is an industrialized city having over one million populations and is located near several active faults. Finite fault modeling with a dynamic corner frequency has adopted here for simulation of future large earthquake. Target fault is North Tehran fault with the length of 110 km and rupture of west part of the fault which is closest to Karaj, assumed for this simulation. For seven rupture starting points, acceleration time series in the site of Karaj Caravansary -historical building-are predicted. Peak ground accelerations for those are vary from 423 cm/s 2 to 584 cm/s 2 which is in the range of 1990 Rudbar earthquake (M w =7.3) . Results of acceleration simulations in different distances are also compared with attenuation relations for two types of soil. Our simulations show general agreement with one of the most well known world attenuation relations and also with one of the newest attenuation relation that hase developed for Iranian plateau.