Decadal Monitoring of Seismic Velocity Changes Beneath Izu‐Oshima, Central Japan, Using Ambient Seismic Noise Records

Abstract This study monitors the seismic velocity changes beneath the Izu‐Oshima volcano, central Japan, using ambient seismic noise records from 2003 to 2020. Applying seismic interferometry to the continuous waveform data from 24 seismic stations, we observed significant temporal variations in the seismic velocity structure. The seismic velocity rapidly decreased following several large earthquakes, including the 2011 magnitude 9.1 Tohoku‐oki earthquake. The observed rapid velocity changes are primarily attributable to dynamic stress changes caused by the earthquakes, suggesting high stress sensitivity in this area. In addition, we identified periodic velocity changes with a 400–500‐day period cycle, which dominate in the 0.5–2.0 Hz frequency range and at stations near the volcano vent. These periodic changes are temporally correlated with crustal deformation detected through geodetic observations, suggesting that strain change is linked to seismic velocity fluctuations in the crust. The observed velocity changes can thus be explained by the strain change, although additional effects, such as fluid migration associated with the velocity reduction, cannot be ruled out. These findings highlight the complex interplay between seismic velocity changes and crustal deformation.