Existence of low-velocity zones under the source areas of the 2004 Chuetsu and 2007 Chuetsu-oki earthquakes inferred from travel-time tomography

Junichi Nakajima, Akira Hasegawa

Research output: Contribution to journalArticlepeer-review

15 Citations (Scopus)

Abstract

Travel-time tomography reveals the presence of highly heterogeneous seismic velocity structures around the source areas of the 2004 Chuetsu and 2007 Chuetsu-oki earthquakes. A prominent low-velocity zone present below the Moho under the source areas of the two events is probably formed by fluids being conveyed through a small-scale upwelling in the mantle wedge. A low-velocity zone distributed in the lower crust below each source area is attributable to fluids supplied from the uppermost mantle to the source area. Since this region with these two source areas is exceptional in that the low-velocity zone is distributed in the uppermost mantle but no Quaternary volcanoes are formed at the surface, a relatively large amount of fluids may be stored below the source areas. These localized fluids may have reduced the strength in the lower crust as well as in the fault zones in the upper crust and, consequently, have promoted a brittle failure in the seismogenic layer. Relocated hypocenters of aftershocks of the two events become several kilometers shallower than the original locations determined by the Japan Meteorological Agency, suggesting the importance of using the three-dimensional velocity model in locating the hypocenter.

Original languageEnglish
Pages (from-to)1127-1130
Number of pages4
Journalearth, planets and space
Volume60
Issue number11
DOIs
Publication statusPublished - 2008

Keywords

  • Chuetsu earthquake
  • Chuetsu-oki earthquake
  • Fluids
  • Low-velocity zone
  • Mantle upwelling
  • Seismic tomography

ASJC Scopus subject areas

  • Geology
  • Space and Planetary Science

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