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Abnormal tsunamis caused by the June 13, 1984, Torishima, Japan, earthquake

Satake, Kenji and Kanamori, Hiroo (1991) Abnormal tsunamis caused by the June 13, 1984, Torishima, Japan, earthquake. Journal of Geophysical Research B, 96 (B12). pp. 19933-19939. ISSN 0148-0227. doi:10.1029/91JB01903.

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An earthquake with an M_S = 5.6 (m_b=5.5) which occurred near Torishima, Japan, on June 13, 1984, generated abnormally large tsunamis (tsunami magnitude M_t = 7.3) for its relatively small earthquake magnitude. The maximum amplitude of the tsunamis is not a simple function of distance as the magnitude formula implies. In order to quantify the abnormal tsunamis, we modeled the tsunami source using a finite difference computation on the actual bathymetry. The source of these abnormal tsunamis is modeled as a water surface displacement, with a radius of 12 km and maximum water height of 13 cm. The displaced water volume is 4×10^(13) cm^3, and the potential energy is calculated as 2×10^(17) ergs. If this water displacement is due to a fault motion at 5 km depth, a moment magnitude M_w is estimated to be 6.3. This value is larger than M_w estimated from seismic waves by 0.7, but smaller than M_t by 1.0. The former difference suggests that the earthquake source is very different from an ordinary faulting. If we assume the source is a horizontally lying tensile crack at shallow depth (about 2 km), that explains both the water surface displacement and the seismic moment tensor. The tensile crack is interpreted as an injection of material, as suggested by a seismological study. The discrepancy between M_w and M_t indicates that the propagation path is responsible for the observed large tsunamis. The numerical computation shows a focusing of energy during the propagation of the tsunami along the shallow Izu-Bonin ridge system. Thus the abnormally large tsunamis from the Torishima earthquake are a result of both source and path effects.

Item Type:Article
Related URLs:
URLURL TypeDescription
Satake, Kenji0000-0002-3368-3085
Kanamori, Hiroo0000-0001-8219-9428
Additional Information:© 1991 The American Geophysical Union. Paper number 91JB01903. Received June 5, 1989; Revised March 4, 1991; Accepted June 19, 1991. We used the bathymetry dataset JTOPOl compiled by M. Okada, Meteorological Research Institute, Japan. This work was supported by USGS grant 14-08-001-01356 and NSF grant EAR 89-15987. K.S. is also supported by a Fellowship for Research Abroad from the Japan Society for the Promotion of Science. Contribution 4768, Division of Geological and Planetary Sciences, California Institute of Technology.
Funding AgencyGrant Number
NSFEAR 89-15987
Japan Society for the Promotion of Science (JSPS)UNSPECIFIED
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Other Numbering System NameOther Numbering System ID
Caltech Division of Geological and Planetary Sciences4768
Issue or Number:B12
Record Number:CaltechAUTHORS:20141105-145104212
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Official Citation:Satake, K., & Kanamori, H. (1991). Abnormal tsunamis caused by the June 13, 1984, Torishima, Japan, earthquake. Journal of Geophysical Research: Solid Earth, 96(B12), 19933-19939. doi: 10.1029/91jb01903
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:51332
Deposited On:05 Nov 2014 23:32
Last Modified:10 Nov 2021 19:09

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