Counts of occurrence per depth in 渡島・檜山地方

Counts of occurrence per depth in 渡島・檜山地方 (Oshima,Hiyama region) is shown as below graph,

1km's count was the most one before M't Usu's eruption in 2000. After it, 10km's one becomes the most. It was occurred after the longest silent term (almost seven years) of 1km earthquakes. 10km's curve increased also by it, and there had been increased between 1995/11-2000/3. The increase of 10km seems to be occurred by M6.3 (20km) in 1993/8. Addition to it, M6.3 in 1993 may be occurred M6.1 (120km) in 1992. They had performed one chain reaction. Long silent terms were often found on the curves of shallow depths like as in 1km/10km/20km especially, and the rapid increase of the counts are occurred after them with high accuracy. In curves of deeper ones, the interval themselves are long in general.  So, there should be difficult to be found out the longer silent term than it.