Counts of occurrence per depth in 新潟県下越沖

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

The count of 1km-30km curves was increased rapidly by M7.5 of 30km in 1964. The M7.5 is the greatest one of all depths. Even though the 1km's count became large especially, the rank went down to the 2nd because of the longest silent term of 1km between 1965-2005. Since the end period, there has been any more 1km occurrence, yet. During the stop of 1km, 10km curve has overtaken 1km curve. 20km/30km curves are following them. Other depth's counts are far less.     

• 10km (yellow)…The count is the 1st. After the longest silent term of 10km between 1919-1964, 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. By the 2nd rapid increase in 1995, the count of 10km curve became the 2nd. The next major rapid increase was caused by M6.7 of 10km in 2019. By the increase, the count of 10km became the 1st by far. The largest one of 10km is this M6.7 in 2019. 
• 1km(red)…The count is the 2nd. Before the M7.5 of 30km in 1964, it was the 1st by far. There were 2 twice long silent terms before the M7.5. One was between 1929-1944 (the 4th). The other was between 1929-1944 (the 3rd). They may be the signs of the M7.5 in 1964. By the M7.5, the count of 1km was accelerated rapidly. The silent terms became shorter suddenly, and the longest silent term was occurred between 1965-2005. The next silent term is still extending as the 2nd length of 1km. During it, 10km curve had overtaken 1km curve. The largest one of 1km is M6.1 in 1964. 
• 20km(orange)…The count is the 3rd. Before the M7.5 of 30km in 1964, the count rank was the 2nd though far from 1km. After the rapid increase by the M7.5, the silent terms of 20km became longer suddenly. In result, the rank has gone down to the 3rd. The largest one of 20km is M6.1 in 1964.
• 30km(yellow green)…The count is the 4th. After the longest silent term of 30km between 1924-1964, there was the rapid increase by M7.5 of 30km in 1964. As same as 20km, the silent terms of 30km became longer suddenly. On addition to it, the terms of 30km were longer than 20km's ones. The largest one of 30km is M7.5 in 1964. The M7.5 was also greatest one of all depths.
• 40km(green) …The count is the 5th. There were the continuous long silent terms as the 2nd & the 1st. Each term is between 1919-1944/1944-1964.As same as 1km-20km curves, there was the rapid increase by the M7.5 of 30km in 1964. But, the increase had stopped suddenly in 1964 on the way. Since the stop in 1964, the longest silent term has been extending still. The largest one of 40km is M6.0 in 1964. 
• others…omitted.