GNSS Observation and Monitoring of the Hakone Volcano and the 2015 Unrest

Abstract

In recent years, earthquake swarm activities have occurred at the Hakone Volcano in the western area of Kanagawa Prefecture, Japan, with a frequency of once in several years. Global Navigation Satellite System (GNSS) observations have detected the inflation of volcanic edifice during these activities. Hot Springs Research Institute of Kanagawa Prefecture (HSRI) regularly observes crustal deformation for monitoring seismic and volcanic activities by using 16 sites of GNSS observation, which were installed in the western area of Kanagawa Prefecture. These observed data, together with those from other agencies, are analyzed routinely, and time-series graphs, displacement vector diagrams, and strain maps are illustrated to monitor seismic and volcanic activities. Given that GNSS monitoring detected the baseline extension about half a month or a month before the earthquake swarm activities, a stacking analysis is routinely performed for early detection of the extension. Some of the analysis results can be found on the website of HSRI. The Hakone Volcano had the largest earthquake swarm activity beginning at the end of April 2015, and a phreatic eruption occurred in Owakudani at the end of June 2015. The GNSS observed crustal deformation, which indicated the inflation of the volcanic edifice in early April 2015. This inflation can be explained by a volume change of a point pressure source located about 6.5 km below sea level.