Attenuation of ground-motion spectral amplitudes in central and eastern Iran

In this study, more than 2769 seismograms of 633 earthquakes recorded by 18 stations of the Iranian Seismological Center (IRSC) during 2006–2016, were used to estimate the spectral attenuation relation for strong ground motion in central and eastern Iran. First, In frequency domain by using a local regression smoothing method (robust LOWESS), through considering Hinged trilinear function, the distances at which the nature of geometrical spreading attenuation changes significantly was graphically found in 80 km and 124 km distances. Then, using a brute force optimization, it's found that b1 = −1.11 ± 0.27, b2 = 0.09 ± 0.22, and b3 = −0.70 ± 0.23 minimize the average absolute value of the Fourier spectrum amplitude residuals. Finally, the direct quality factor Q in the study region is obtained as Q = 166 ± 1.08f0.62±0.02, using an anelastic attenuation coefficient at different frequencies. The geographical distribution of station corrections at 1 Hz shows a positive station correction for east and the southeastern part of Iran in Kerman province. •Estimation of the average attenuation relation parameters in the Central and eastern Iran•2769 records due to 633 earthquakes recorded at 18 stations of the Iranian Seismological Center during 2006–2016 were selected.•Establish of the shape of the attenuation curve of the Fourier spectrum of acceleration for finding graphically the distances at which the nature of geometrical spreading attenuation changes significantly.•using of local regression smoothing method (robust LOWESS), through considering Hinged trilinear function•The regression analysis has determined that Fourier spectral amplitudes for the shear window follow a hinged trilinear attenuation model.•The results indicate that the attenuation curve for ground motion amplitudes in the frequency domain has three distinct sections with two hinged points at distances of 80 and 124 km.•Determination of the shear wave quality function Using an anelastic attenuation coefficient at different frequencies