The continuous estimation of changes in seismic velocity and seismic
scattering property by passive interferometry using seismic ambient
noise is a promising tool for monitoring volcanoes. To improve the
usefulness of this method, it is necessary not only to detect subsurface
structural changes but also to quantitatively compare the estimated
changes in seismic wave velocity and seismic wave scattering property
with other observations such as ground deformation. We applied passive
interferometry to continuous seismic records from Suwanosejima volcano,
Japan, recorded between April 2017 and December 2021. We detected
repeated significant waveform decorrelations in seismic ambient noise
cross-correlation functions, indicating seismic scattering property
changes in the shallow areas of the volcano. These decorrelations were
observed from 2 week to a few days before the increase in the number of
explosions, suggesting that seismic scattering properties changed
significantly during that period. We found that the timing of the
decorrelation in seismic ambient noise cross-correlation functions and
tilt changes related to magma accumulation and injection beneath
Suwanosejima were well synchronized. The high correlation between the
amounts of decorrelation and tilt change during the magma accumulation
period suggests that a large volume of accumulated magma caused great
changes in the scattering property. These results provide a significant
first step toward a quantitative comparison of the amount of changes in
the scattering property with the amount of magma accumulation beneath
volcanoes.