Source Scaling and Ground-Motion Variability along the East Anatolian Fault

Abstract

We investigate the source scaling and ground-motion variability of 1585 earthquakes with Mw>3 occurring along the East Anatolian fault since 2010. We compile a dataset of 17,691 Fourier amplitude spectra of S waves recorded by 186 stations. A spectral decomposition is applied to isolate the source contribution from propagation and site effects. Source spectra are fit with Brune’s model to estimate seismic moment and corner frequency and to compute the stress drop Δσ. The 10th, 50th, and 90th percentiles of the Δσ distribution are 0.18, 0.51, and 1.69 MPa, respectively, and the average Δσ increases with earthquake magnitude. For the two mainshocks of the 2023 sequence, the estimated Δσ is about 13 MPa, significantly larger than the Δσ of the smaller events. At intermediate and high frequencies, the interevent residuals are correlated with Δσ. When recorded peak ground accelerations and velocities for Mw<6 are compared with the predictions from ground-motion models proposed in the literature, the negative value of the average interevent residuals is consistent with low values of Δσ. Contrariwise, the average residuals for the peak parameter of the Mw 7.8 and 7.5 mainshocks of the 2023 sequence are almost zero, but with distance dependencies.