[S03-5] Imaging of heterogeneities in the Earth with seismic scattered waves and ambient noise V

[S03-5-01] Depth dependence of stress sensitivity of seismic velocity changes as inferred from noise correlation analyses at Izu-Oshima volcano, Japan

^○Tomoya Takano, Takeshi Nishimura, Hisashi Nakahara (Department of Geophysics, graduate School of Science, Tohoku University)

We determine stress sensitivity of seismic velocity changes at Izu-Oshima in Japan based on a seismic interferometry method. Ambient noises recorded at four seismic stations deployed on the small volcano island for 4 years from January 2012 to December 2015 are used to calculate cross correlation functions. Cross correlation functions are estimated at frequency bands of 0.5-1Hz, 1-2Hz, and 2-4Hz. Applying a moving window time analysis to the cross correlation functions, we estimate daily seismic velocity changes. Decrease and increase of seismic velocity changes are well associated with the areal strain changes observed by GNSS network. Comparing the areal strain changes with seismic velocity changes, we calculate the stress sensitivity of seismic velocity changes to be (7.1+/-1.3)x10-8 Pa-1 at the frequency band of 0.5-1Hz, (1.4+/-0.1)x10-7 Pa-1 at 1-2Hz, and (1.3+/-0.1)x10-7 Pa-1 at 2-4Hz, respectively. The stress sensitivity of seismic velocity at 0.5-1Hz is lower than those at the higher frequencies. The observed seismic velocity changes are located in the upper 1 km by assuming the wave length of Rayleigh-wave. The result at Izu-Oshima is consistent with the stress sensitivity of seismic velocity changes by previous studies. We conclude, therefore, that the stress sensitivity of seismic velocity changes decreases with depth down to a few kilo meters, which is probably due to the increase of confining pressure.