Causes of the N–S compressional aftershocks of the E–W compressional 2008 Iwate–Miyagi Nairiku earthquake (M7.2) in the northeastern Japan arc

Sumire Maeda, Toru Matsuzawa, Keisuke Yoshida, Tomomi Okada, Takeyoshi Yoshida

Research output: Contribution to journalArticle

Abstract

In this study, we investigated the influence of local structural heterogeneities on aftershocks of the 2008 Iwate–Miyagi Nairiku earthquake (M 7.2) that occurred in the northeastern Japan arc. Although this area is characterized by an E–W compressional thrust faulting stress regime, many N–S compressional thrust-type and strike-slip-type earthquakes were also observed in the aftershock activity of the 2008 event. The occurrence of such N–S compressional aftershocks indicates that the differential stress was very low before the main shock. We investigated Vp/Vs structure in the aftershock area in detail to find most of the area showed Vp/Vs as low as less than 1.70, which is consistent with the previous studies. Our result shows, however, the aftershock area was dotted with high Vp/Vs small areas, which suggests the locations of abundant fluid-filled cracks. The comparison of the distributions of Vp/Vs, the stress changes due to the mainshock, and focal mechanisms of the aftershocks indicate that the N–S compressional aftershocks are concentrated in regions with high Vp/Vs and large N–S compressional stress change. From these results, we concluded that the N–S compressional aftershocks occurred in regions with low strength due to the high pore pressure and with N–S compressional stress caused by the stress change due to the mainshock in a low differential stress regime.[Figure not available: see fulltext.]

Original languageEnglish
Article number94
Journalearth, planets and space
Volume71
Issue number1
DOIs
Publication statusPublished - 2019 Dec 1

Keywords

  • Fluid
  • Geological structure
  • Heterogeneous structure
  • Microearthquakes
  • Stress field

ASJC Scopus subject areas

  • Geology
  • Space and Planetary Science

Fingerprint Dive into the research topics of 'Causes of the N–S compressional aftershocks of the E–W compressional 2008 Iwate–Miyagi Nairiku earthquake (M7.2) in the northeastern Japan arc'. Together they form a unique fingerprint.

  • Cite this