Abstract
We present some singular characteristics of the 2011 off the Pacific coast of Tohoku Earthquake in comparison with other megathrust earthquakes, such as the 1960 Chilean and the 2004 Sumatra-Andaman earthquakes. In addition to the conventional along-strike segmentation, along-dip segmentation of the fault area or subduction zone is an important feature for the Tohoku subduction zone, as indicated by the difference in background seismicity: virtually no seismicity in shallow segments but active with large events repeating in deep segments. The interaction between along-dip segments (deep and shallow segments) led to the great 2011 Tohoku earthquake. The along-dip segmentation results in plane or two-dimensional rupture propagation on a coseismic fault. Significant along-strike variability is also important for the 2011 Tohoku earthquake, with segments of both weak (e.g., slow or tsunami earthquakes) and strong plate couplings located adjacent to each other. In contrast, every segment appears to be with strong plate coupling for other megathrust earthquakes. One exception is the 1964 Alaska earthquake that shares a certain degree of common characteristics with the 2011 Tohoku earthquake: two distinct seismogenic zones along the dip direction of the trench, that is, the along-dip segmentation is noticeable. Significant along-strike variability also characterizes the activities in and around the subduction zone of the 1964 Alaska earthquake, including a creeping segment and a tsunami-earthquake segment.
Highlights
The 2011 off the Pacific coast of Tohoku, Japan, Earthquake of JMA magnitude 9.0 occurred on 11 March, 2011, in the most intensively investigated subduction zone in the world
In addition to the conventional along-strike segmentation, along-dip segmentation of the fault area or subduction zone is an important feature for the Tohoku subduction zone, as indicated by the difference in background seismicity: virtually no seismicity in shallow segments but active with large events repeating in deep segments
While the 1960 Chilean and 2004 Sumatra earthquakes are different from the 2011 Tohoku earthquake, we find some similarity in several characteristics between the 1964 Alaska earthquake and the 2011 Tohoku earthquake
Summary
The 2011 off the Pacific coast of Tohoku, Japan, Earthquake of JMA magnitude 9.0 occurred on 11 March, 2011, in the most intensively investigated subduction zone in the world. Megathrust earthquakes had been believed to occur commonly in a so-called Chilean-type subduction zone (e.g., Kanamori, 1977; Uyeda, 1982; Lay et al, 1982). The 2011 Tohoku earthquake appears to lack these major characteristics of megathrust earthquakes of the Chileantype subduction zones the number of examples is limited. For the 2011 Tohoku earthquake, we notice remarkable along-strike variability in the behavior of seismogenic zones, reflecting highly spatially heterogeneous plate coupling. We compare these characteristics with other earthquakes. While the 1960 Chilean and 2004 Sumatra earthquakes are different from the 2011 Tohoku earthquake, we find some similarity in several characteristics between the 1964 Alaska earthquake and the 2011 Tohoku earthquake
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