Abstract

We study source, path, and site effects for eastern Iran earthquake, based on regression analysis of 243 three‐component Fourier acceleration spectra from 32 eastern Iran earthquakes with moment magnitude M 4.4–7.4, recorded at hypocentral distances from 5 to 250 km. The geometric spreading follows a trilinear behavior. The first and second hinges of the trilinear behavior are at 87 and 119 km, respectively. The associated quality factor (Q) based on the horizontal components is Q(f)=166f1.13. The site‐dependent parameters κ0 for vertical and horizontal components are 0.035 and 0.048, respectively. Because of lack of station‐specific site information, the horizontal‐to‐vertical ratio is considered to be a rough estimation of generic site amplification. The mean value of Brune stress drops estimated for the events is 81 bars. To construct an empirical model for source spectra (horizontal component of the shear‐wave spectrum), for M 4.4–7.4, we tested several functional forms, including those suggested for California and eastern North America, to search for the best combination of the coefficients that minimizes the average residual errors. The model we attained is a function of two multiplicative corner frequencies of fa and fb and a parameter forumla: forumla, in which log(fa)=2.69−0.56M, log(fb)=3.40−0.53M, and forumla.

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