The frequency spectra of body waves from near and distant earthquakes are investigated by the use of a set of analogue band-pass filters, each having an octave band width in frequency. The seismic waves are separated into five frequency bands ranging from 0.5 to 40 cycles per second. The filtered wave signals are amplified and recorded continuously on a multi-channel ink-writing oscillograph. Some of the results of the present analysis based on the observations since December, 1965 may be summarized as follows. 1) From the attenuation curves of the amplitude ratio of two different frequency bands obtained from many near earthquakes, the minimum Q value of P waves in the earth's crust and the upper-most mantle is estimated at about 500. 2) The ratio of the spectral amplitude of the teleseismic P waves at 2 cps to that at a lower frequency than 1 cps increases generally with the focal depth. A remarkable fact is that the amplitude ratio for earthquakes with the focal depth from 100 to 200 km in Fiji Islands is small as compared with that for the other focal depth ranges suggesting a possible effect of the low velocity channel. On the contrary, two exceptional shocks in Central Asia with shallow depths indicate a larger amplitude ratio at 2 cps channel than that of deep earthquakes and may be suggested as man-made explosions.
近地地震ならびに遠震実体波についてのスペクトル構造をしらべるため,周波数分析装置を試作した.試作した装置はアナログ方式であり, 0.5サイクルから40サイクルの周波数範囲について,5組の濾波器により分類し,その出力はオリジナルの記録と共に6成分のインク書きオツシログラフによって連続記録をおこなっている.
雑誌名
東京大學地震研究所彙報 = Bulletin of the Earthquake Research Institute, University of Tokyo
巻
44
号
3
ページ
873 - 891
発行年
1967-01-30
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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Frequency Analysis of Seismic Waves (1)
ji0443005.pdf
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