oa 3-D Seismic Image beneath Hakone Volcano, Japan

Hakone volcano is located in the northern part of Izu peninsula. It is well known as inactive volcano and hot springs resort. But sometimes there are earthquake swarms. There was big earthquake swarm in April 2001. Total number of earthquakes was 15,816 during April to October. The cause of this activity is not yet solved. Explosion observation was carried out and 3-D velocity structure was estimated using explosions and micro earthquakes hybrid inversion method to know where magma exists or not. Not only micro earthquakes but also explosions were used, so the high resolution subsurface image and velocity value can be obtained with good accuracy. As results, we can find some faults as lines of hypocenter beneath Hakone volcano, and there is no results that suggests existence of magma. So it is considered that the cause of swarm earthquakes activity that occurred on 2001, was not activity of magma.