Investigation of deep and lateral changes of coda wave quality factor using short-time Fourier transform in northwest of Iran

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Abstract

The present study attempts to explore the characteristics of seismic coda wave energy attenuation using single back scattering in northwestern Iranian plateau. For this purpose, the short-time Fourier transform is used to separate the frequency bands. To estimate quality factor, coda waves from more than 1600 small crustal events with magnitudes ranging from 2 to 5 Ml and epicenteral distances of less than 200 km have been used. In this study, coda wave quality factor has been calculated at 7 lapse times of 30 to 90 s. The results show that the best fitted line comes from lapse time of 40 s and the frequency relation is in the form of Q = (103±1)f(0.88±0.04). Relatively small values of Q0 indicate that there is high heterogeneity in the shallow layers of the region of northwestern Iran that can be due to the relatively high seismicity of the region. This is in line with our expectations of the crustal structure and the existence of Sahand and Sabalan volcanoes. The presence Sahand and Sabalan volcanoes in the region has created a warm crust in this area. On the other hand, the relationship between quality factor and temperature changes exponentially, and the quality factor decreases with increasing temperature. Moreover, the relationship between low values of the frequency with parameter n indicates high seismicity, active tectonics and the presence of large heterogeneities in the region. Existence of North Tabriz fault and many fractures in this region is one of the reasons for the high heterogeneity in this region.

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References

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Volume 7, Issue 3
January 0
Pages 241-251

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