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Earth Planets Space, Vol. 64 (No. 12), pp. 1189-1198, 2012
doi:10.5047/eps.2012.04.011

Variability of megathrust earthquakes in the world revealed by the 2011 Tohoku-oki Earthquake

Junji Koyama, Kazunori Yoshizawa, Kiyoshi Yomogida, and Motohiro Tsuzuki

Earth and Planetary Dynamics, Graduate School of Science, Hokkaido University, Sapporo 060-0810, Japan

(Received January 10, 2012; Revised April 10, 2012; Accepted April 27, 2012; Online published January 28, 2013)

Abstract: The seismicity of the Pacific coast of Tohoku, Japan, has been investigated in detail and characterized into regional seismic segments. The 2011 megathrust earthquake of Mw 9.0 on 11 March ruptured almost all of the segments in that area, causing devastating tsunamis. The prime factor that had not been recognized before is the double segmentation along the Japan trench: The apparent absence of earthquakes in the trench-ward segments as opposed to the Japan Island-ward segments that have repeated smaller earthquakes. We term this pattern of seismic activity 'along-dip double segmentation (ADDS)'. The 2011 Tohoku megathrust earthquake is typical of a class of great earthquakes different from that of the 1960 Chile earthquake, in which a young and buoyant plate is subducting rapidly under the continental plate. In the 1960 Chile case, the seismic activity is characterized by 'along-strike single segmentation (ASSS)', where there is weak seismic activity before the main event all over the plate interface of the subduction zone. We study the greatest earthquakes around the world and find that there is a variety of megathrust earthquakes characterized by ASSS to ADDS, where the 2004 Sumatra-Andaman, the 1960 Chile, the 1964 Alaska and the 2011 Tohoku-oki earthquakes are typical end-members.
Key words: Megathrust earthquake, along-dip double segmentation, along-strike single segmentation, 2011 Tohoku, 1964 Alaska, 1960 Chile, 2004 Sumatra-Andaman, multiple segments.


Corresponding author E-mail: koyama@mail.sci.hokudai.ac.jp


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