Eliminating site effects from surface station secords and improving earthquake early warning parameters

Document Type : Research Article

Authors

1 Ph.D, Department of Earth Sciences, Science and Research Branch, Islamic Azad University, Tehran, Iran

2 گروه علوم زمین، واحد علوم و تحقیقات، دانشگاه آزاد اسلامی، تهران، ایران.

3 Professor, Institute of Geophysics, University of Tehran,Tehran, Iran

Abstract

Earthquake early warning parameters play an important role in issuing of a warning and reducing casualties caused by earthquakes. Site effects are one of the factors that affecting the values of earthquake early warning parameters (, , ,  and B). In this study, in order to investigate the site effects on the values of earthquake early warning parameters, 1830 earthquake accelerograms recorded at the six KiK-net accelerometery stations in Japan between 2008 and 2020, were used. These accelerograms were recorded at the surface and borehole stations. Short time Fourier transform (STFT) as well as deconvolution tool were used to remove the site effects from the accelerograms in the time-frequency domain. After removing the site effect from the waveforms of the surface stations, the values of all the earthquake early warning parameters, especially ,  and B, were improved and became closer to the values obtained from the bedrock. The results show that the early warning parameters  and  have the minimal influence from site effects and also behave on surface and borehole stations similarly. In general, the values of the frequency-dependent early warning parameters  and  increase after modifying the site effect on the vertical component. In contrast, the parameters , and  were reduced at all stations. After modification of the site effect, the difference between the calculated values of all parameters on the surface and bedrock are decreased, which indicates the improvement of the results of earthquake early warning systems in estimating the earthquake source parameters.

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References

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Iranian Journal of Geophysics
Volume 15, Issue 3
December 2021
Pages 59-72

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