Counts of occurrence per depth in 新潟県下越地方

Counts of occurrence per depth in 新潟県下越地方（Kaetsu region, Niigata Pref.）is shown as below graph, 

Until 2005, the count of 1km was the 1st. As there was the longest silent term of 1km between 1968-2003, 10km curve has overtaken 1km curve. 20km / 30km curves are following behind 10km curve. 40km curve has stopped in 1964 on the way of it. These common rapid increase was induced by M7.5 of 30km in 1964.

• 10km (yellow)…The count is the 1st. After the longest silent term of 10km between 1931-1963, there was the rapid increase by M7.5 of 30km in 1964. The next rapid increase was caused by M5.6 of 20km in 1995. Then, the count of 10km has been increasing steadily. The largest one of 10km is M5.2 in 1964. 
• 1km (red)…The count is the 2nd. The count was the 1st until 2005. The largest one of 1km is M5.4 induced by M7.5 of 30km in 1964. There is the longest silent term of 1km between 1968-2003. After it, the silent terms became shorter suddenly. The occurrence of 1km stopped in 2008. Before the stop, 10km curve overtook 1km curve.
• 20km(orange)…The count is the 3rd. 20km curve was following behind 1km curve. The first rapid increase was induced by the M7.5 of 30km in 1964. After it, the silent terms became longer in parallel with the longest silent term of 1km. The next rapid increase was occurred by M5.6 of 20km as same as 10km curve. By the M5.6, 20km curve was overtaken by 10km curve in 1995. Since 1995, 20km has been following behind 10km curve. The largest one of 20km is M6.1 in 1964.
• 30km(yellow green) …The count is the 4th. The major rapid increase was caused by M7.5 of 30km in 1964. After it, there were the long silent terms of the 3rd(between 1965-1982)/2nd(1984-2007)/4th(2010-2023). In result, the count of 30km becomes less than shallower earthquakes by far. The largest one of 20km is M6.1 in 1964. The largest one of all depths is the M7.5 of 30km in 1964. 
• 40km(green)…The count is the 5th. The major rapid increase was caused by M7.5 of 30km in 1964. But, the increase stopped on the way of it in 1964. The largest one of 40km is twice M4.2s in 1964. 
• others…omitted.