%0 Journal Article
%T Attenuation of Fourier spectra for 2012 Aharâ€“Varzaghan earthquakes, Northwestern Iran
%J Journal of the Earth and Space Physics
%I Institute of Geophysics, University of Tehran
%Z 2538-371X
%A Samaei, Meghdad
%A Miyajima, Masakatsu
%A Nojima, Nobuoto
%D 2015
%\ 12/22/2015
%V 41
%N 4
%P 23-38
%! Attenuation of Fourier spectra for 2012 Aharâ€“Varzaghan earthquakes, Northwestern Iran
%K Ahar-Varzaghan earthquakes
%K Attenuation
%K Fourier spectra
%K Geometrical spreading
%K Northwestern Iran
%K quality factor
%R 10.22059/jesphys.2015.56029
%X In this research, we have used 102 strong motion recordings from 2012 Ahar-Varzaghan earthquakes (Mw=6.5 and Mw=6.3) to study the form of attenuation of shear wave Fourier amplitude spectra of those two events. The analysis is carried out in a broad-band frequency range from 0.1 to 20 Hz. A bilinear shape for geometrical spreading is assumed based on nonparametric regression of the data. The hinge point of the bilinear shape is around 60 km away from the earthquake source; the geometric spreading forms for the first and second segments are R-0.9 and R-0.5, respectively. The results of this study show that there is considerable dependency of the rate of geometrical spreading on frequency. If only frequencies above 1 Hz are considered, the first segment of geometrical spreading will have a slope steeper than R-1. In contract, for lower frequencies it has a gentle slope. The associated quality factor for the assumed shape of geometrical spreading (appropriate for frequencies logarithmically spaced between 0.1 to 20 Hz) is Q(f)=148 f 0.62. The estimated Q(f) in this study agrees well with the other estimated shear wave quality factors in the region; however, if the whole attenuation model (consisted of geometrical spreading and quality factor) is considered, there will be conspicuous differences between different models.
%U https://jesphys.ut.ac.ir/article_56029_a5b68556855166cb70a4ddb97739ef52.pdf