Rupture process of the Ito–Oki, Japan, earthquake of 1989 July 9 and interpretation as a trigger of volcanic eruption

Abstract

The rupture process of the Ito–Oki, Japan, earthquake (MJ 5.5) of 1989 July 9 was studied in detail by waveform inversion, and the relation between this earthquake and the July 13 volcanic eruption on the Teishi Knoll near the epicentre was discussed. We used strong motion seismograms recorded at near‐field stations operated by the Earthquake Research Institute and the Japan Meteorological Agency. The inversion method for estimating spatial and temporal slip distribution is essentially the same as that of Yoshida & Koketsu (1990). The estimated fault model showed that large slip occurred in the epicentral area extending eastward for about 1 km at a depth of 5 km. We calculated the volumetric strain change due to the estimated slip and found that a remarkable pressure drop occurred just under the Teishi Knoll. A model of volcanic eruption by Ida (1990) suggests that such a pressure drop in a magma reservoir causes vesiculation of dissolved volatiles in the magma and leads to magma ascent toward a surface eruption. We attempted to quantitatively explain the process of the Teishi Knoll eruption in terms of Ida's model considering the Ito–Oki earthquake to be a trigger of the eruption. Copyright © 1992, Wiley Blackwell. All rights reserved