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Mechanism of tsunami earthquakes

Kanamori, Hiroo (1972) Mechanism of tsunami earthquakes. Physics of the Earth and Planetary Interiors, 6 (5). pp. 346-359. ISSN 0031-9201. doi:10.1016/0031-9201(72)90058-1.

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The mechanism of the Aleutian islands earthquake of 1946 and the Sanriku earthquake of 1896 is studied on the basis of the data on seismic waves from 5 to 100 s and on tsunamis. These earthquakes generated, despite their relatively small earthquake magnitude, two of the largest and most widespread tsunamis in history. The data obtained at different periods are interpreted in terms of the effective moment, M_e. The effective moment at a certain period is defined as a seismic moment of a virtual step function dislocation that explains the observation at this period. The effective moment of the tsunami earthquakes increases rapidly towards 0.5 to 1.0 × 10^(29) dyne · cm as the period increases while, for ordinary earthquakes, it is more or less constant. This dependence can be explained in terms of a source deformation having a time constant of about 100 s. The M_c versus ƒ (frequency) diagram provides a diagnostic method of estimating the tsunami potential of earthquakes. If the M_e - ƒ diagram for an earthquake has a steep upgrade towards low frequency implying an effective moment exceeding 10^(28) dyne · cm at zero frequency, the earthquake has a high tsunami potential. Since the determination of the effective moment at various periods can be made by a simple procedure, this method could be incorporated in the tsunami warning system. The abnormal slow deformation at the source of the tsunami earthquakes may be a manifestation of viscoelasticity of a weak zone beneath the inner margin of the trenches. The weak zone which is implied by large normal-fault earthquakes such as the 1933 Sanriku and the 1929 Aleutian islands earthquakes may be a result of frictional heating at the interface between the oceanic and the continental lithospheres.

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Kanamori, Hiroo0000-0001-8219-9428
Additional Information:© 1972 Published by Elsevier B.V. Received 24 April 1972. This paper was stimulated by discussions with Professor Kinjiro Kajiura in connection with the striking difference between the 1896 and the 1933 Sanriku earthquakes. Professor Kajiura made many valuable suggestions on the analysis of tsunami data.Professor Lynn Sykes kindly sent me a preprint of his paper from which I greatly benefited. He also informed me of the uncertainty in the depth of the 1929 earthquake in the in Aleutians. Conversations with Professor Kazuaki Nakamura were very helpful in increasing my knowledge on the possibility of sea-bottom slumps. Dr. Hideo Watanabe kindly provided me with useful information on the seismographs and the intensity scale used in Japan in 1896. To these colleagues I express my sincere thanks. The seismograms used in the present study were kindly supplied by many seismological observatories in the world and of the Japan Meteorological Agency, the names of which, however, are too numerous to mention here. I would like to express my sincere thanks to these observatories. The assistance by Miss Tatoko Hirasawa throughout this study is gratefully acknowledged.
Group:UNSPECIFIED, Division of Geological and Planetary Sciences
Issue or Number:5
Record Number:CaltechAUTHORS:20150217-150630656
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Official Citation:Hiroo Kanamori, Mechanism of tsunami earthquakes, Physics of the Earth and Planetary Interiors, Volume 6, Issue 5, 1972, Pages 346-359, ISSN 0031-9201, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:54889
Deposited By: Ruth Sustaita
Deposited On:18 Feb 2015 03:52
Last Modified:10 Nov 2021 20:39

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