Counts of occurrence per depth in 内浦沖

Counts of occurrence per depth  in 内浦湾（Uchiura Bay）is shown as below graph,

10km/1km's counts seems to be related with M't Usu's volcanic activity. There was no occurrence or only once in each depth of 30-90km. More than M6.0 was occurred as only M6.1 in 120km.

10km(yellow)…The count is the 1st. 3 days ago of M't Usu's eruption in 2000/3/31, the counts of 10km/1km started increasing rapidly, and continued about for a week. There had been also the advanced rapid increase of 10km in 1997. It had started when the count catch up with 1km. The largest one is M5.3 in 2016. 

1km(red)…The count is the 2nd. Just before the rapid increase in 2000, there had been the longest silent term between 1989-2000. The largest one is M5.2 in 1955. The last occurrence was in 2021.

20km(orange)…The count is the 3rd. The longest silent term is between 1945 - 1974. The curve's slope became steeper since 2020. The largest one is M4.4 in 2021.

120km(gray)…The count is the 4th. The longest silent term is between 1938 - 1992. It was stopped by M6.1 in 1992 as the largest one of all depths. The 2nd largest is M5.4 in 2007, and the last occurrence of 120km.

130km(gray)…The count is the 5th. The first occurrence is M5.1 as the largest of 130km. 

others …omitted. Their counts are only 1 or 0.