Counts of occurrence per depth in 北海道北西沖

Counts of occurrence per depth in 北海道北西沖 (Northwest offshore Hokkaido region) is shown as below graph, 

All 3 earthquakes more than M6.0 were occurred in deeper than 230km. M4.8 is the max in 1km-60km. 

• 1km (Red)…This count of the earthquakes is the 1st. Before M4.5 in 1965, all of 1km were "unknown details" with no data of the magnitude. The M4.5 is the largest one in this depth.
• 10km(yellow)…The count is the 2nd. There was a longest silent term between 1919-1993. In late 2010s, the count increased with 20km rapidly, and it overtook 20km's one. It may also overtake 1km's one in near future. The the largest magnitude in this depth is M3.7 in 2024.
  
• 20km(orange)…The count is the 3rd. There was a longest silent term between 1919-1968. In late 2010s, the count increased with 10km rapidly. The the largest magnitude in this depth is M4.8 in 2013.
• 30km(light green)…The count is the 4th. There was a longest silent term between 1956-1996. The the largest magnitude in this depth is M4.6 in 2016. 
  
• 40km(green)…There was only once as M4.3 in 1978.
• 50km… No occurrence
• 60km(blue) … There was only once in 1952. But, the magnitude is unknown.
• Others…There are few in 240km-330km. But, all 3 earthquakes more than M6.0 were occurred in these depth as shown in the chart above.