Document Type : Original Article
Authors
1
1. Assistant Professor, Department of Civil engineering, Nowshahr Branch, Islamic Azad University, Nowshahr, Iran,
2
2. M.Sc., Department of Civil engineering, Nowshahr Branch, Islamic Azad University, Nowshahr, Iran,
3
3. Associate Professor, Department of Physics, Qom Branch, Islamic Azad University, Qom, Iran,
Abstract
Seismic wave attenuation is one of the important features of the earth's structure. Studies performed on it show that the attenuation of seismic waves is related to seismicity, tectonics and physical characteristics of the wave propagation environment and is expressed as the inverse quality factor (Q). The aim of this study is to estimate the shear wave quality factor by spectral decay method for Razavi Khorasan and South Khorasan, enclosed at 32º-36º north latitude and 56º-62º east longitude, which is located in the seismic tectonic state of East-Central Iran and has been destroyed many times by destructive earthquakes. For this purpose, the quality factor of shear waves (QS) for seven frequency bands 1-2, 2-4, 3-6, 4-8, 6-12, 8-16 and 12-24 Hz with central frequencies 1.5, 3, 4.5, 6, 9, 12 and 18 Hz for study area, using accelerometric data recorded from the earthquake of May 10, 1997,Ghaen-Ardakul, by the accelerator network, affiliated to the Housing and Urban Development Research Center (BHRC) , It is estimated. Based on the results, the frequency dependence relationship of the; direct S wave's quality factor is, and for component, L is, also, the relationship of frequency dependence of the average quality factor of shear waves of two horizontal components has been obtained. The value of the quality factor obtained in the reference frequency of 1 Hz (Q0) is less than 200. This indicates that the study area is not only tectonically and seismically active, but also has high absorption and heterogeneity. The results are consistent with the sedimentary structure of the area. Also, the results obtained in this study for Q0 and the relationship between frequency dependence and research conducted for other seismic regions of Iran (such as Avaj, Ardabil located in northwestern Iran) and some other parts of the world (such as Kanto region in Japan, region Kech in Gujarat, India), is well matched and the high absorption and small quality factor estimated for the study area is expected. In general, regions that are similar in terms of tectonics and geology have similar values of quality factor and frequency dependence.
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