The activity of deep low frequency earthquakes beneath Fuji volcano became vigorous since October 2000. Hypocenters were distributed about 15km deep under Fuji volcano. Our seismic observation detected not only low frequency earthquakes but also high frequency ones. According to our observation, 20 to 40 high frequency earthquakes have been occurring in a year and shallow earthquakes have been also observed. The shallow seismicity has not changed associated with the low frequency earthquakes activity and no crustal deformation has been observed by tiltmeters and others. Therefore, these are not thought as urgent signals for volcanic eruptions.
Examples of high frequency earthquake (upper) and low frequency earthquakes (lower) observed at the station situated at the summit of Fuji volcano.
Monthly number of low frequency earthquakes at Fuji volcano (until 31 October 2007).