Source process of very long period seismic events associated with the 1998 activity of Iwate Volcano, northeastern Japan

Takeshi Nishimura, Haruhisa Nakamichi, Satoru Tanaka, Minemori Sato, Tomokatsu Kobayashi, Sadato Ueki, Hiroyuki Hamaguchi, Masakazu Ohtake, Haruo Sato

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59 Citations (Scopus)

Abstract

We observed very long period seismic events that are associated with the 1998 activity of Iwate Volcano, northeast Japan. The events show a dominant period of 10 s and duration of 30-60 s, often with accompanying short-period waves at the beginning and at the end of the long-period signals. By analyzing the broadband seismograms we find that the source elongates in the east-west direction for ∼ 4 km at a depth of 2 km beneath the western part of Iwate Volcano. Results of moment tensor inversions show a source mechanism of mutual deflation and inflation of two chambers located at the western and eastern edges of the source region. The source region coincides with the low seismic velocity zone detected by seismic tomography and is very close to the locations of pressure sources estimated from crustal deformation data. On the basis of these results we infer that the very long period seismic events are generated by transportation and movement of magmatic fluid (hot water and/or magma) in a shallow part of the volcano. We further present a simple source model of very long period seismic events based on one-dimensional flow dynamics and propose a new parameter to characterize the size of very long period event: the energy flow rate, which is obtained by dividing the seismic moment by the dominant period. The energy flow rate was estimated as 3.1 × 1012 J/s for the event on July 29, 1998.

Original languageEnglish
Article number2000JB900155
Pages (from-to)19135-19147
Number of pages13
JournalJournal of Geophysical Research: Solid Earth
Volume105
Issue numberB8
DOIs
Publication statusPublished - 2000 Aug 10

ASJC Scopus subject areas

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

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