Region-Specific Key Seismic Parameters for Earthquakes in Northern Iran

Abstract

Strong-motion accelerograms recorded within northern Iran are used to examine the propagation characteristics of shear wave, including geometric spreading behavior, Q-value, j 0 , and horizontal-to-vertical (H/V) ratio. These region-specific key seismic parameters are estimated from 259 three-component records of 22 earth- quakes with magnitude ranging from M 4.9 to M 7.4 in northern Iran. The geometric spreading follows a trilinear behavior with a strong postcritical reflection from the Moho. The first and second hinges of the trilinear behavior are at 75 and 150 km, respectively. The associated Q-value, based on the vertical component is Q 87 f 1.46 . j0 value for vertical and horizontal components are 0.03 and 0.05, respec- tively. Because of lack of station-specific site information, the H/V ratio is considered to be a rough estimation of generic site amplification. The obtained region-specific parameters are used to estimate the average stress drop based on three stochastic modeling approaches. Stochastic point-source modeling suggests a Brune stress drop of 125 bars, whereas stochastic finite-fault modeling based on static and dynamic corner frequency approaches suggests a stress drop of 68 bars.