Earthquake characteristics before eruptions of Japan's Ontake volcano in 2007 and 2014

We detect earthquakes associated with Japan's Ontake eruptions in 2007 and 2014 using the match-and-locate method. Thirty-seven times more events (4949) than the Japan Meteorological Agency (JMA) catalog (133) and 30 times more events (1880) than the JMA catalog (62) are detected during the eruptions of 2007 and 2014, respectively. The detected earthquakes are further classified into three different types: long-period (LP) events, LP-associated events, and volcano-tectonic (VT) earthquakes. Both LP and LP-associated events are observed in the two eruptions. We suggest that the observed intense seismicity before both eruptions indicates the rewaking of Ontake volcano and might be used to predict its impending eruption in the long term. The temporal persistence and spatial concentration of LP and LP-associated events may be used to predict the eventual eruption and eruption location, and the maximum magnitude of the LP events may be used as an indicator of eruption magnitude.