On the Nature of the 20°—Discontinuity in the Earth’s Mantle
The structure of the earth’s mantle, mainly its upper part, having been investigated by the analysis of seismic waves of five Kamchatka-Kurile Islands earthquakes of shallow focus and some others, the problems on the existence and property of the 20°-discontinuity and the low-velocity layer in the m...
Published in: | Tellus A: Dynamic Meteorology and Oceanography |
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Stockholm University Press
1958
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Online Access: | http://dx.doi.org/10.3402/tellusa.v10i1.9211 https://account.a.tellusjournals.se/index.php/su-j-tadmo/article/download/3573/6703 |
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crstockholmup:10.3402/tellusa.v10i1.9211 2024-06-02T08:09:43+00:00 On the Nature of the 20°—Discontinuity in the Earth’s Mantle Nishimura, Eiichi Kishimoto, Yoshimichi Kamitsuki, Akira 1958 http://dx.doi.org/10.3402/tellusa.v10i1.9211 https://account.a.tellusjournals.se/index.php/su-j-tadmo/article/download/3573/6703 unknown Stockholm University Press https://creativecommons.org/licenses/by/4.0 Tellus A: Dynamic Meteorology and Oceanography volume 10, issue 1, page 137-144 ISSN 1600-0870 journal-article 1958 crstockholmup https://doi.org/10.3402/tellusa.v10i1.9211 2024-05-07T14:17:31Z The structure of the earth’s mantle, mainly its upper part, having been investigated by the analysis of seismic waves of five Kamchatka-Kurile Islands earthquakes of shallow focus and some others, the problems on the existence and property of the 20°-discontinuity and the low-velocity layer in the mantle are discussed in some detail. The time-distance graphs obtained in Japan are in fair agreement with JEFFREYS-BULLEN’s Table (1939), and also the 20°-discontinuity is considered to exist certainly at nearly the same depth as given by Jeffreys. The amplitude relation observed at the epicentral distance near 20° between the direct wave propagating through the medium entirely above the 20°-discontinuity and the refracted wave penetrating down into that discontinuity is just the reverse of that commonly expected, that is, the former being small and the latter large, both for the P- and S-waves. Concerning this phenomenon some arguments are given. Moreover, the existence of a new discontinuity was ascertained at some depth below the 20°-discontinuity, as deduced from the appearance of a prominent later phase. As to the existence of a low-velocity layer in the mantle, it is somewhat questionable at least in the form after Gutenberg from the analysis of seismic waves observed at the stations in Japan of the earthquakes of Kamchatka-Kurile Islands. But its existence is still probable in some forms, which is uncertain at present, at some depths below the Mohorovi?i? discontinuity. This problem will be postponed to a succeeding paper. Article in Journal/Newspaper Kamchatka Stockholm University Press Tellus A: Dynamic Meteorology and Oceanography 10 1 137 144 |
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Stockholm University Press |
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The structure of the earth’s mantle, mainly its upper part, having been investigated by the analysis of seismic waves of five Kamchatka-Kurile Islands earthquakes of shallow focus and some others, the problems on the existence and property of the 20°-discontinuity and the low-velocity layer in the mantle are discussed in some detail. The time-distance graphs obtained in Japan are in fair agreement with JEFFREYS-BULLEN’s Table (1939), and also the 20°-discontinuity is considered to exist certainly at nearly the same depth as given by Jeffreys. The amplitude relation observed at the epicentral distance near 20° between the direct wave propagating through the medium entirely above the 20°-discontinuity and the refracted wave penetrating down into that discontinuity is just the reverse of that commonly expected, that is, the former being small and the latter large, both for the P- and S-waves. Concerning this phenomenon some arguments are given. Moreover, the existence of a new discontinuity was ascertained at some depth below the 20°-discontinuity, as deduced from the appearance of a prominent later phase. As to the existence of a low-velocity layer in the mantle, it is somewhat questionable at least in the form after Gutenberg from the analysis of seismic waves observed at the stations in Japan of the earthquakes of Kamchatka-Kurile Islands. But its existence is still probable in some forms, which is uncertain at present, at some depths below the Mohorovi?i? discontinuity. This problem will be postponed to a succeeding paper. |
format |
Article in Journal/Newspaper |
author |
Nishimura, Eiichi Kishimoto, Yoshimichi Kamitsuki, Akira |
spellingShingle |
Nishimura, Eiichi Kishimoto, Yoshimichi Kamitsuki, Akira On the Nature of the 20°—Discontinuity in the Earth’s Mantle |
author_facet |
Nishimura, Eiichi Kishimoto, Yoshimichi Kamitsuki, Akira |
author_sort |
Nishimura, Eiichi |
title |
On the Nature of the 20°—Discontinuity in the Earth’s Mantle |
title_short |
On the Nature of the 20°—Discontinuity in the Earth’s Mantle |
title_full |
On the Nature of the 20°—Discontinuity in the Earth’s Mantle |
title_fullStr |
On the Nature of the 20°—Discontinuity in the Earth’s Mantle |
title_full_unstemmed |
On the Nature of the 20°—Discontinuity in the Earth’s Mantle |
title_sort |
on the nature of the 20°—discontinuity in the earth’s mantle |
publisher |
Stockholm University Press |
publishDate |
1958 |
url |
http://dx.doi.org/10.3402/tellusa.v10i1.9211 https://account.a.tellusjournals.se/index.php/su-j-tadmo/article/download/3573/6703 |
genre |
Kamchatka |
genre_facet |
Kamchatka |
op_source |
Tellus A: Dynamic Meteorology and Oceanography volume 10, issue 1, page 137-144 ISSN 1600-0870 |
op_rights |
https://creativecommons.org/licenses/by/4.0 |
op_doi |
https://doi.org/10.3402/tellusa.v10i1.9211 |
container_title |
Tellus A: Dynamic Meteorology and Oceanography |
container_volume |
10 |
container_issue |
1 |
container_start_page |
137 |
op_container_end_page |
144 |
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