Seismological Studies on Magma Ascent Process of failed eruption based on degassing

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We present seismological studies of Mt. Ontake, which relate to the small eruption in 2007. We determined the hypocenter locations beneath the summit of Mt. Ontake. The focal depths are from 0.5 to 2.0 km below sea level. We conducted a moment tensor inversion to determine the location and source mechanisms of a very-long-period (VLP) event, which occurred on 25 January 2007. The VLP source was located at 600 m above see level beneath the summit and explained by volumetric changes in an inclined crack at the source. We also conducted S-wave splitting measurements to estimate spatial variations and temporal changes of seismic anisotropy associated with the eruption in 2007. The polarization angles show no significant change before or after the eruption, as the eruption was so small.