Mt. Zao is an active volcano located in northeastern Honshu and has histories of phreatic or phreato-magmatic eruptions in the last 2 ka. Unrest of Zao volcano started in January, 2013 with a volcanic tremor followed by activated seismicity mainly in the lower crust and very long-period seisimic events (VLP) up to today. GNSS data obtained around the volcano for the period from January to July in 2015 demonstrate radial horizontal displacements and uplifting (shown in the figure), suggesting the pressurized magma source estimated in the summit caldera at a depth of around 4 km below sea level.
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