Volcanism of Mount Fuji activated by the 2011 Japanese large earthquakes

The relation between earthquakes and volcanic eruptions, each of which is manifested by large-scale tectonic plate and mantle motions, has been widely discussed. Mount Fuji in Japan last erupted in 1707, paired with a magnitude (M)-9-class earthquake that took place 49 days prior. Motivated by this pairing, previous studies examined the effect of both the 2011 M9 Tohoku megaquake and a triggered M6-class earthquake 4 days later at the foot of the volcano on Mount Fuji, although no volcanic eruption was reported. More than 300 years already have passed since the last 1707 eruption, and although consequences to humans and society caused by the next eruption are already being considered, the implication for future volcanism remains uncertain. Here we show how volcanic low-frequency earthquakes (LFEs) in the deep part of the volcano revealed hitherto-unrecognized activation immediately after the foot earthquake. Our analyses using statistical methods based on the matched-filtering, the epidemic-type aftershock sequence (ETAS), and the Gutenberg-Richter frequency-magnitude distribution of LFEs show that despite an increase in the rate of occurrence of LFEs, these did not return to pre-earthquake levels, indicating a change in the magma system. Our results demonstrate that the volcanism of Mount Fuji was reactivated by the foot earthquake, implying that this volcano is sufficiently sensitive to external events that are enough to trigger eruptions.