Fig. 11

Frequency–depth variations of volcano-tectonic earthquakes in the hydrothermal system during post-2001 volcanic unrest episodes. Frequencies of every 500 m depth interval are shown. Upper panels; frequency–depth variations of a) pre- b) co- and c) post-eruptive volcanic unrests. Lower panel d) shows cumulative frequency–depth variations for each volcanic unrest episode. We count the number of earthquakes with epicenters within 2 km of the summit of Kamiyama (35.2333º N 139.0208 º E). Here, the earthquakes during volcanic unrest are defined as those occurring within 6 months of the initial date. The initial dates and total number of earthquakes (N) are shown in the upper right of d). The hypocenter catalog is obtained by the routine analysis by the Hot Springs Research Institute of Kanagawa Prefecture. Error of hypocenter location is estimated by square of the diagonal element of the error covariance matrix as 0.05 km (NS), 0.06(EW), and 0.14 km (depth). Note that hypocenter depths for earthquakes shallower than 0 km are not well constrained