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タイトル: 1973年浅間火山噴火に伴う爆発地震について : (第1報)スペクトル解析
その他のタイトル: Explosion Earthquakes Associated with the 1973 Eruptions of Asama Volcano : (Part I) Spectral Studies
著者: 今井, 博
行田, 紀也
小山, 悦郎
著者(別言語): Imai, Hiroshi
Gyoda, Noriya
Koyama, Etsuro
発行日: 1979年11月30日
出版者: 東京大学地震研究所
掲載誌情報: 東京大学地震研究所彙報. 第54冊第1号, 1979.11.30, pp. 161-186
抄録: Asama Volcano, located in the central part of Honshu, commenced an eruption at the summit crater on Feb. 1 in 1973 after 11 years'quiescence and a series of explosive eruptions continued until April 26 of the same year. The data of three component seismograms analysed in this paper were recorded by long-period seismographs (T0 = 5.0 sec) at the seismic station NAKANOSAWA located 4.2 km east of the summit crater and were registered on smoked paper recording drums at the Asama Volcano Observatory. Power spectral analyses were carried out separately, by use of the Maximum Entropy method and the Fast Fourier Transform method for both the initial parts and the later parts, of the explosion earthquakes that exceeded 1015 ergs in seismic energy. The results of the spectral studies are as follows: 1) As to the initial parts (5 sec from on-set) of seismic waves, N-S components prevail in longer periods against E-W components. 2) As to the later parts (51.2 sec after 10 sec from on-set), the results are contrary to 1). Moreover, E-W components of Feb. 1 and Mar. 10 resemble each other. The other components (U-D, N-S), however, are different from each other. Particularly, it should be emphasized that the maximum value of the spectrum for the U-D component is found at about 0.2 Hz on Feb. 1 but at about 0.7-1.3 Hz on Mar. 10. 3) Sweep maximum amplitudes (or running diagrams) for E-W components have splittings at about 1.4-1.6 sec. 4) Predominant periods of the initial part of seismic waves on running diagrams change and/or separate into other periods. As the results of these analyses, it is recognized that the explosion earthquake on Feb. 1 is different from others on the mechanism, particularly, from that on Mar. 10. In addition, it is characteristic that the spectra of the later parts for E-W components, which are in a radial direction from the summit crater, are stable in shape. It is obvious that these results give some clue to the knowledge of the mechanism of explosion earthquakes, and of eruptions.
URI: http://hdl.handle.net/2261/12724
ISSN: 00408972


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