Counts of occurrence per depth in 十勝沖

 Counts of occurrence per depth in 十勝沖 (Tokachi offshore region) is shown as below graph,  

The count of 1km has been down from the 1st to 5th after the longest silent term between 1978 - 2024. On the other hand, 50km's count has been up to the 1st. M8.1 of 50km was occurred at the triple junction of 50km/40km/10km. 6 days later, M6.9 of 70km was also occurred at the triple junction of 70km/80km/60km. The M8.1 is the greatest one of all depths (1km's one is only M6.3). M8.1 may be transferred to 1km by domino effect in some day. 

• 50km(light blue)…This count is the 1st. 50km/40km have been overtaking and being overtaken.As 40km overtook had long silent term between 1942 - 1948, 50km overtook 40km. Then, by M8.2 of 50km in 1952, 40km had more aftershocks and overtook 50km again. Later, 50km caught up with 40km by M7.0 of 50km in 1971. Around 1986, the become more steep, and 1km went into the longest silent term. So, the curve becomes top. The greatest earthquake of all depth is M8.2 of 50km in 1952. The M8.2 was occurred at the triple junction of 50km/40km/10km. 6 days later, M6.9 of 70km was also occurred at the triple junction of 70km/80km/60km. 
• 40km(green)…This count is the 2nd. As described above, 50km/40km have been overtaking and being overtaken. But, the largest magnitude of 40km is M6.9 in 1961 (far less than M8.2 of 50km). The count doesn't reach to 50km. 
• 60km(blue)…This count is the 3rd. The count has been increased smoothly.  The largest magnitude of 60km is M6.4 in 1943. 
• 30km(yellow green)…This count is the 4th. 30km/20km had the double junction at M7.1 of 20km in 2003. The count jumped up after the M7.1 on the same count with 20km. The largest magnitude of 60km is M7.1 in 2008. 
• 1km(red)…This count is the 5th. There was the longest silent term between 1978 - 2024. Before it, the count was the 1st. The largest magnitude of 1km is M6.3 in 1926.   
• 70km(purple)…This count is the 6th. As described above, M6.9 of 70km was occurred at the triple junction of 70km/80km/60km in 1952. M7.1 was occurred the next count became the same as 30km after the long silent term of 30km. The largest magnitude of 60km is M7.1 of the triple junction in 1962.   
• 20km(orange)…This count is the 7th. M7.1 was occurred at the double junction of 20km/30km in 2003. The M7.1 is the greatest magnitude of 20km. After 2021, the curve slope has become steep. So, there is a possibility of the rapid increase in near future. 
• 80km(navy)… This count is the 8th. There was a steep slope increase around M7.1 of 70km in 1962. The largest magnitude of 80km is M6.4 in 1983. 
• 100km(gray)… This count is the 9th.The largest magnitude of 100km is M5.6 in 1926. 
• 10km(yellow)… This count is the 10th. In past, it was 4th after M8. 2 of 50km for a time. But, the silent terms became longer. The largest magnitude of 10km is M6.7 in 1936. 
• others…omitted.