Attenuation of Fourier spectra for ۲۰۱۲ Ahar–Varzaghan earthquakes, Northwestern Iran
Publish place: Journal of the Earth and Space Physics، Vol: 41، Issue: 4
Publish Year: 1394
نوع سند: مقاله ژورنالی
زبان: English
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JR_JESPHYS-41-4_003
تاریخ نمایه سازی: 26 مهر 1402
Abstract:
In this research, we have used ۱۰۲ strong motion recordings from ۲۰۱۲ Ahar-Varzaghan earthquakes (Mw=۶.۵ and Mw=۶.۳) 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 ۰.۱ to ۲۰ 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 ۶۰ km away from the earthquake source; the geometric spreading forms for the first and second segments are R-۰.۹ and R-۰.۵, respectively. The results of this study show that there is considerable dependency of the rate of geometrical spreading on frequency. If only frequencies above ۱ Hz are considered, the first segment of geometrical spreading will have a slope steeper than R-۱. 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 ۰.۱ to ۲۰ Hz) is Q(f)=۱۴۸ f ۰.۶۲. 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.
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Authors
Meghdad Samaei
Postdoctoral Researcher, Graduate School of Natural Science and Technology, Kanazawa University, Kanazawa, Japan
Masakatsu Miyajima
Professor, Graduate School of Natural Science and Technology, Kanazawa University, Kanazawa, Japan
Nobuoto Nojima
Professor, Department of Civil Engineering, Gifu University, Gifu, Japan
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