Counts of occurrence per depth in 国後島付近

Counts of occurrence per depth in 国後島付近 (Kunashiri Island)  is shown as below graph, 

Only 1km's count has been stood out. On the other hand, the other shallow 10km/20km's counts are very low. The curves except 1km/50km were jammed around M6.9 of 30km in 1980. As same as it, the curves except 1km/10km/30-50km were also jammed around M7.2 of 100km in 1978. 

• 1km(red)…This count of the earthquakes is the 1st. Before M5.4 in 1924, all of 1km were "unknown details" with no data of the magnitude. 7 months later  from M5.4, M6.9 was occurred in 1925. Both M6.9 of 1km in 1925/of 30km in 1968 are the 2nd greatest in all depths (The 1st was M7.2 of 100km in 1978). The longest silent term is continuing since 1994 after the 2nd one between 1982-1994. The 1km earthquakes occurred in 1994 were aftershocks of M8.2 (Hokkaido East offshore Earthquake). The epicenter (of 30km) was out of this area.
• 50km(light blue)…The count is the 2nd since 1955. Recently, 50km is the most active depth. The the largest magnitude in this depth is M5.9 in 1979.  
  
• 40km(green)…The count is the 3rd. 40km curve had overlapped with 30km since M6.7 in 1964. But, there was a rapid increase by M8.2 (Hokkaido East offshore Earthquake) in 1994. After the aftershocks of 40km, there was a long silent term 1994-2005. Then, the count has started the increase again after it. The largest magnitude in this depth is M6.7 in 1964.  
  
• 70km(purple)…The count is the 4th. The curves of 70km/60km is overtaken and being overtaken. The largest magnitude in this depth is M5.7 in 1994.  
  
• 80km(navy)…The count is the 5th. The curve almost stays between 70km and 90km. Before M8.2 (Hokkaido East offshore Earthquake) of 30km in 1994, there had been the rapid slope of 90km between 1992-1994. After M8.2, the rapid slope was taken over by 80km. In recent years, the curve is approaching 70km. The largest magnitude in this depth is M6.3 in 1994.  
  
• 60km(blue)…The count is the 6th. The curves of 60km/70km is overtaken and being overtaken. The largest magnitude in this depth is M5.7 in 1994.   After around 2010, the silent term has the tendency of becoming longer. So, 70km/80km curves overtook 60km. As the silent terms became longer since 2010,  the count rank became lower. The largest magnitude in this depth is M6.2 in 1929.  
  
• 30km(yellow green)…The count is the 7th. Though the curves of 30km/40km was overtaken and being overtaken, no significant increase of the count wasn't occurred after M8.2 (Hokkaido East offshore Earthquake) in 1994. On addition to it, there was the longest silent term between between 1995-2013.  The largest magnitude in this depth is M6.9 in 1968. As the value is large, the count should become greater than now in future.
• 90km(brown)…The count is the 8th(100km's curve is the 9th). Though the curve was following 80km until M7.2 of 100km in 1965, it was delayed from 80km after the M7.2. The largest magnitude in this depth is M5.9 in 1957. 
• 20km(orange)…The count is the 10th. There were 2 times major rapid increases after both M6.9 of 30km in 1980 and M6.8 of 30km in 1980.  After the long silent term between 1987-2011, the count has been accelerated. The largest magnitude in this depth is M6.3 in 2018.
• 10km(yellow)…The count is the 11th. As same as 20km, this shallow 10km is also low rank of counts. The longest silent term of 10km is continuing since 1995. The largest magnitude in this depth is M5.6 in 1934. The value is less than 20km's largest value of M6.3. So, the update may be still far in the future.
• Others…omitted.