Counts of occurrence per depth in 十勝地方南部

Counts of occurrence per depth in 十勝地方南部 (South 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 M6.0 in 1927. But, the the increase has stopped in 1982. The max magnitude is only M5.4 in 1928.
• 50km(light blue)…This count is the 2nd. Around 50km in depth, the counts are larger than others of shallow depths.There were some long silent terms. The longest one was between 1941-1950, and the 2nd one was between 1989- 1998. After both long terms, the counts had increased faster. After overtaking the curves of 60km/70km, there was the max magnitude of M6.1 in 2012.
• 60km(blue)…This count is the 3rd. After M6.7 in 1970, the curve's slope became steeper. The curves of 60km/70km have been overtaken by each other. Since 2004, 60km's curve overtakes 70km's one. Both of them haven't been affected by M6.1 of 50km in 2012. The max magnitude is M6.7 in 1970, and it is also the max in all depths. 
  
• 70km(purple)…This count is the 4th. The max magnitude is M5.6 in 1979. The curve seems to overtake 60km again in future.
• 40km(green)…This count is the 5th. The count of 40km/30km were increased by M6.7 of 60km in 1970 rapidly. But, the curve of 30km couldn't overtake 40km. The max magnitude is M6.0 in 1927.
• 100km(gray) …This count is the 6th. After M6.5 in 2013, the curve overtook 30km, then 80km also. The max magnitude is M6.5 in 2013.
• 80km(navy blue)…This count is the 7th. The curve has overtaken by 100km in 2024. The max magnitude is only M5.6 in 1925.
• 30km(yellow green)…This count is the 8th.The max magnitude is only M5.0 in 1931.     
• 10km(yellow)…This count is the 9th even though shallow depth. The last occurrence was in 2011 before M6.1 of 50km in 2012. The max magnitude is only M5.0 in 1941.
• 20km(orange)…This count is the 10th even though shallow depth. The last occurrence was in Jun/1970 after M6.7 of 60km in Jan/1970 . The max magnitude is only M5.1 in 1952.
  
• 120km(gray) …This count is the 11th. The max magnitude is M6.6 in 1987.