Evidence for subsurface magma bodies beneath Izu-Oshima volcano inferred from a seismic scattering analysis and possible interpretation of the magma plumbing system of the 1986 eruptive activity

Abstract

Observed seismic waveforms were analyzed to find the distribution of seismic scatterers beneath Izu-Oshima volcano in an island located about 100 km south of Tokyo, Japan, using seismic waveforms generated by earthquakes, whose epicentral distances are from several tens to about a thousand kilometers. The method employed in the study was developed based on a prestack migration of shot gathers and is composed of the following procedure: (1) static correction, (2) the estimation of waveforms incident into a volume of interest, i.e., subsurface structure of the volcano, and (3) an inverse procedure using the developed migration scheme. The location of scatterers and the order of scattering became clear with the present analysis. The petrological implications and results from geoelectromagnetic studies by other researchers agree with the proposed model in which the existence of main and submagma reservoirs beneath the volcano were indicated. These results are interpreted in terms of a model on the magma migration path during the 1986 eruptive activity of the volcano. Seismic scattering analysis played a significant and indispensable role in this study to give a direct view of a possible underground plumbing system, and is considered a promising method for revealing the unknown structure of volcanoes in the future.