Spectral content and decay characteristics with time of the coda waves from local earthquakes are studied using the data of narrow band-pass niters of six stations distributed in the Kanto district, Japan, and some properties of the effects of attenuation, excitation and radiation at the source on the coda waves are obtained. The decay characteristics of coda waves determined at a given station are independent of the epicenter location and source size, and depend only upon the duration time measured from the origin time as suggested by AKI (1969). The apparent Q derived from the coda waves at four stations increase with frequency, approximately proportionally to the square root of the frequency, with the values increasing from 120-250 at 0.75 Hz to 800-2500 at 24 Hz. The coda excitation at the six stations located on different geological formations also depends on frequency. The difference of coda amplitudes measured at the same lapse time between the stations located on the sediment and the granitic rocks is, on the average 20 times at 0.75 Hz and less than 1/10 at 24 Hz. This behavior suggests the differences in intrinsic Q and inhomogeneity size of the earth's crust beneath the station. The scaling laws of the earthquake source spectra are constructed using the spectral ratios of coda source factors and the source spectrum of the smallest earthquake used in the estimation of coda source factors. The local variation of the source spectrum is found within the area of the Kanto district, which may be attributed to the difference in rupture strength of the earth's crust.
雑誌名
東京大學地震研究所彙報 = Bulletin of the Earthquake Research Institute, University of Tokyo
巻
53
号
1
ページ
1 - 48
発行年
1978-08-15
ISSN
00408972
書誌レコードID
AN00162258
フォーマット
application/pdf
日本十進分類法
453
出版者
東京大学地震研究所
出版者別名
Earthquake Research Institute, University of Tokyo
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Spectral Analysis of the Coda Waves from Local Earthquakes
ji0531001.pdf
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