Remotely-triggered seismicity in the Hakone volcano following the 2011 off the Pacific coast of Tohoku Earthquake

Seismic activity in the Hakone volcano at an epicentral distance of 450 km was remarkably activated just after the 2011 off the Pacific coast of Tohoku Earthquake. More than 1600 events were observed in the caldera of the volcano, from 15:00 on March 11 to 12:00 on April 2. To clarify the relationship between the occurrence of the main shock and the induced activity in the Hakone volcano, we investigated the spatial distribution of hypocenters and temporal changes of the seismicity, and we examined seismographs of the main shock to identify small local events during the passage of the surface waves. Hypocenters determined with the double-difference method are mostly distributed in the N-S direction, showing several clusters of seismicity. Focal mechanisms of major earthquakes are predominantly strike-slip having the P axis in the NNW-SSE direction. These features of the hypocenter distribution and the focal mechanisms are consistent with those of earthquakes that occur ordinarily in the Hakone volcano. The onset of the local event was initiated during the Love and Rayleigh waves from the main shock, suggesting that large dynamic stress changes of 0.6 MPa dominantly contributed to initiate the sequence of seismic activity.