Absolute gravity change associated with the March 1997 earthquake swarm in the Izu Peninsula, Japan

Shigeo Yoshida, Gaku Seta, Shuhei Okubo, Shigeki Kobayashi

Research output: Contribution to journalArticlepeer-review

14 Citations (Scopus)


We carried out both absolute and relative gravity measurements in the Izu Peninsula just before and after the March 1997 earthquake swarm occurred. The measurements revealed significantabsolute gravity changes, which we find to be made of three spatial components. The first one is located near Cape Kawana, and would be associated with the volcanic activity that caused the earthquake swarm. The second one would be associated with shallow and localized magma intrusion just beneath Ito. The third one may be due to a change in the deep region beneath the Kita-Izu fault system, which is considered to be a major tectonic line of this region. The gravity changes can be used to detect underground mass movement. For this purpose, we first use crustal movement observations to construct an elastic dislocation model with two tensile faults and a left lateral fault.Then we use the gravity changes to constrain the density of the material which filled the tensile faults. We find that the density is likely to be small, and that the gravity changes of the first component are reproduced well by the fault model. The smallness of the density implies that highly vesiculated magma or water would have injected into the faults.

Original languageEnglish
Pages (from-to)3-12
Number of pages10
Journalearth, planets and space
Issue number1
Publication statusPublished - 1999
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Geology
  • Space and Planetary Science


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