Detailed imaging of the fault planes of the 2004 Niigata-Chuetsu, central Japan, earthquake sequence by double-difference tomography

Tomomi Okada, Tadashi Yaginuma, Norihito Umino, Toru Matsuzawa, Akira Hasegawa, Haijiang Zhang, Clifford H. Thurber

Research output: Contribution to journalArticlepeer-review

29 Citations (Scopus)

Abstract

Imaging of the hypocentral faults of the Niigata-Chuetsu earthquake sequence was performed by double-difference tomography using data obtained by a temporary aftershock observation network densely deployed in the hypocentral region. Two parallel "unfavorly oriented" fault planes steeply inclined to the WNW are revealed, that of the main shock and that of the largest aftershock, as well as a zone of velocity change between the high-velocity footwall and the low-velocity hanging wall for both P- and S-waves. This suggests that the main shock and the largest aftershock are caused by the reactivation of normal faults in the Miocene under the current compressional stress regime. Parts of the fault planes are also found to be located within the low-velocity zone. This low-velocity zone continues to the lower crust, which is imaged by an inversion from the regional data, and would correspond with highly fractured zone around the fault plane with high fluid pressure, which reactivated the "unfavorly oriented" fault and triggered the present earthquake. Large coseismic slip area appears to extend to the northeastern portion with relatively high velocity. This suggests that the asperity (large coseismic slip area) of the main shock possibly correspond with a higher velocity region along the fault plane.

Original languageEnglish
Pages (from-to)32-43
Number of pages12
JournalEarth and Planetary Science Letters
Volume244
Issue number1-2
DOIs
Publication statusPublished - 2006 Apr 15

Keywords

  • Aftershocks
  • Asperity
  • Fault plane
  • Seismic tomography
  • The 2004 Niigata-Chuetsu (Mid Niigata) earthquake

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science

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