12:00 PM - 12:15 PM
[SCG61-05] Groundwater pressure changes at the Ohtaki observatory before and after the 2007 and 2014 eruptions of Mt.Ontake
Keywords:Mt.Ontake, eruption, groundwater, crustal deformaiton
After 1998 there were two eruptions at Mt.Ontake. One is the 2007 eruption, which occurred in March, 2007. The other is the 2014 eruption, which occurred in September 2014. A few months before the 2007 eruption, a relatively large crustal deformation, which was the gradual increase in the length of the baseline crossing Mt Ontake, was observed although no such crustal deformation was observed in the 2014 eruption. At the 2007 eruption the groundwater pressure at GOT dropped 20 cm during almost the same period when the length of the baseline gradually increased. However no such groundwater pressure change was observed in the 2014 eruption. Taking the volumetric strain sensitivity into account, the 20 cm drop in the groundwater pressure means about 100 nstrain increase in the volumetric strain at GOT. The precursory gradual increase in the length of the baseline is converted into about 300 nstrain increase in the linear strain along the baseline. These two values are well-matched.
In the presentation we will report the details of those groundwater pressure changes and the crustal deformation.