Application of two-step GIT on source, path and site effects case study: Mw7.3 Sarpol-e Zahab great earthquake on 12 November 2017

One of the largest earthquakes in the Zagros region occurred on November 12, 2017, in Sarpol-e Zahab with Mw=7.3. We considered the aftershocks of this event and collected the S-wave amplitude spectra from 87 strong-motion records to determine the source, path, and site effects using a non-parametric generalized inversion technique. The grid-searching method based on Brune’s ω2 model was employed to determine some of the source parameters. The corner frequency and seismic moment vary from 1.11 to 5.14 Hz and from 9.12×1014 to 1.36×1017 N.m, respectively. Also, The seismic moment and the cube of corner frequency are inversely related to each other. The stress drop of earthquakes is determined with the ε indicator. In this study ε is equal to 1.91; thus this value indicates that frictional overshoot has occurred with the dynamic frictional stress larger than the final stress. The S-wave quality factor is estimated as Q=101f0.67. The value of Q0 is small, which is characteristic of an active tectonic environment. We compared the site effects that were calculated by GIT and H/V methods. In most cases, a very good agreement was observed and the small difference between them is mainly due to the constraints and assumptions of these methods.