Unusual low-angle normal fault earthquakes after the 2011 Tohoku-oki megathrust earthquake

• Yagi, Yuji

• Okuwaki, Ryo

• Enescu, Bogdan

• Fukahata, Yukitoshi

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.

Journal

• Earth, Planets and Space

  Earth, Planets and Space 67 2015-06-26

  SpringerOpen

Keywords

• 2011 Tohoku-oki earthquake
• Low-angle normal fault earthquakes
• Slip overshoot

Details

• CRID: 1050845760762899328
• NII Article ID: 120005756317
• ISSN: 18805981
• HANDLE: 2433/212424
• Text Lang: en
• Article Type: journal article
• Data Source:
  • IRDB
  • CiNii Articles