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Title: Unusual low-angle normal fault earthquakes after the 2011 Tohoku-oki megathrust earthquake
Authors: Yagi, Yuji
Okuwaki, Ryo
Enescu, Bogdan  kyouindb  KAKEN_id  orcid https://orcid.org/0000-0003-2153-0097 (unconfirmed)
Fukahata, Yukitoshi  kyouindb  KAKEN_id  orcid https://orcid.org/0000-0002-1009-7366 (unconfirmed)
Author's alias: 深畑, 幸俊
Keywords: 2011 Tohoku-oki earthquake
Low-angle normal fault earthquakes
Slip overshoot
Issue Date: 26-Jun-2015
Publisher: SpringerOpen
Journal title: Earth, Planets and Space
Volume: 67
Thesis number: 100
Abstract: A few low-angle normal fault earthquakes at approximately the depth of the plate interface, with a strike nearly parallel to the trench axis, were detected immediately after the 2011 Tohoku-oki earthquake. After that, however, no such normal fault events have been observed until the occurrence of the 2014 M <inf>W</inf> 6.6 Fukushima-oki earthquake. Here we analyze the teleseismic body waveforms of the 2014 Fukushima-oki earthquake. We first compare the observed teleseismic body waves of the 2014 Fukushima-oki earthquake with those of the largest previous low-angle normal fault aftershock (M <inf>W</inf> 6.6), which occurred on 12 March 2011, and then estimate the centroid depth and moment tensor solution of the 2014 Fukushima-oki earthquake. The teleseismic body waves and moment tensor solution of the 2014 Fukushima-oki earthquake are similar to those of the 2011 normal fault aftershock, which suggests that the 2014 Fukushima-oki earthquake occurred at a similar depth and had a similar mechanism to that of the 2011 aftershock. We detected five low-angle normal fault aftershocks at approximately the depth of the plate interface, with a strike nearly parallel to the trench axis, and confirmed that all of them except for the 2014 Fukushima-oki earthquake occurred within 17 days after the mainshock. The occurrence of these low-angle normal fault events is likely to reflect the reversal of shear stress due to overshooting of slip during the 2011 Tohoku-oki earthquake. We speculate that a fast but heterogeneous recovery of stress state at the plate interface may explain why these events preferentially occurred immediately after the megathrust event, while one of them occurred with a significant delay. In order to better understand the characteristics of stress state in the crust, we have to carefully observe the ongoing seismic activity around this region.
Rights: © 2015 Yagi et al. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.
URI: http://hdl.handle.net/2433/212424
DOI(Published Version): 10.1186/s40623-015-0271-6
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