Counts of occurrence per depth in 十勝地方北部

Counts of occurrence per depth in 十勝地方北部 (North Tokachi region)  is shown as below graph,

note : There are not included of all depths to avoid too complicated curves. 

• 1km (red)…This count of the earthquakes is the 1st one. There was a rapid increase of the count after the longest silent term of 1km between 1972-2003 (for 21 years) by M6.8 of 30km in 1931/M6.9 of 70km in 1932. The max magnitude of 1km is M5.7 in 1924. Total max value for all depth is M6.4 of 60km in 1931. After it, there was the 2nd longest silent term of 1km between 1931-1950 (for 19 years). Even though almost 100 year ago, the record has been kept. The count is still growing.
• 10km (yellow)…This count of the earthquakes is the 2nd now. But, the 1st record of the initial occurrence was not so old, in 1969. On addition to it, the 2nd occurrence was in 2000 with 31years silent term. Maybe due to the short term, the max magnitude is only M4.6 in 2020. The count is still on going increasing following 1km's curve. 
  
• 20km-80km…These counts are only 2-4 times. As described above, M6.4 of 60km in 1931 is  the max value for all depths. 
  
• 90km(brown)…This count is the 3rd as same as 120km. But, the last occurrence was in 2012 (13 years ago). There was a little bit rapid increase after the overtaking the curve of 140km until the last occurrence. The max magnitude is only M3.9 in 1996.
• 120km(gray with dot line)…This count is the 3rd as same as 90km. The curve overtook once when it had overtook the curves of 140km&100km in 1972. But, after the long silent term between 1972-1999, the count growth of 90km was more and has overtaken. The last occurrence was in 2015 (10 years ago). The max magnitude is M5.8 in 1944.
• 110km(gray)…This count is the 5th. The max magnitude is M6.3 in 1999, and the value is the 2nd one for all depth. Due to the large Magnitude, the count is still increasing. The rank of count may become higher than 90km/120km within several years.