Open Access

Temporal changes in seismic velocity of the crust around Iwate volcano, Japan, as inferred from analyses of repeated active seismic experiment data from 1998 to 2003

  • Takeshi Nishimura14Email author,
  • Satoru Tanaka14,
  • Teruo Yamawaki14,
  • Hidekazu Yamamoto24,
  • Takashi Sano24,
  • Minemori Sato14,
  • Hisashi Nakahara14,
  • Naoki Uchida14,
  • Shuichiro Hori14 and
  • Haruo Sato14
Earth, Planets and Space201457:BF03352583

https://doi.org/10.1186/BF03352583

Received: 3 December 2004

Accepted: 2 May 2005

Published: 24 June 2014

Abstract

We have examined temporal changes in seismic velocity of the crust through repeated active seismic experiments at Iwate volcano, Japan, where a significant volcanic activity and an M6.1 earthquake were observed in 1998. We apply a cross spectrum moving window technique to seismic data recorded at eight stations for the six explosions detonated from1998 to 2003. The seismic velocity at the frequency range of 3-9 Hz decreased by about 1% during the three months including the occurrence of M6.1 earthquake. The seismic velocity gradually increased, and about one third of the decrease was recovered by 2002. Then, the seismic velocity decreased again in 2003. Spatio-temporal changes in the volumetric strains predicted from the M6.1 fault mechanism and the volcanic pressure sources are well correlated with the seismic velocity changes observed in 1998. However, the predicted stress fields are not completely matched with the observed velocity changes from 1998 to 2003. This inconsistency may be due to unknown regional tectonic stress field and/or localized stress fields induced by volcanic pressure sources. It should be noted that the observed velocity changes indicate frequency dependent characteristics although the mechanism is not yet understood.

Key words

Temporal changes seismic velocity Iwate vocano active seismic experiment