Counts of occurrence per depth in 新潟県上越地方

Counts of occurrence per depth in 新潟県上越地方（Joetsu region, Niigata Pref.）is shown as below graph,  

Most occurrence in this area are occupied with shallow earthquakes (1km-20km). Their major activities were induced by M9.0 Great East Japan Earthquakes. Especially, 1km ones around volcanoes (Niigata-Yakeyama/Shiranesan) were remarkable as the volcanic with the volcanic activities. They also were remarkable around Myoko-san. But, it has kept silent as far as we know. 20km increase stared one year ago of M9.0. It seems one of the sign of M9.0.  

(note:Shiranesan is located at the northwest end of 群馬県北部 North Gunma Pref., and located to next to Niigata Pref.) 

10km (yellow)…The count is the 1st. There were some rapid increases step by step. The largest one was induced by M9.0 Great East Japan earthquake as M6.7 of 10km in 2011. The M6.7 of 10km is the greatest one of all depths. As the increase of the aftershocks of the M6.7 were less than one of 1km, the count rank was 2nd or 3rd between 1923-1999. 20km curve has been increasing steadily. On the way, there was the rapid increase as a continuing earthquakes (max M5.5) in the eastern side of M't Fuji in 1976. The M7.9 in 1923 is the greatest of all depths.      

1km (red)…The count is the 2nd. Between 1923-2000, 1km curve had kept the count as the 1st. But, during the longest silent tern between 1990-2001, 1km curve was overtaken by 10km curve. After it, the silent terms became shorter suddenly, and the short terms had continued until 2021 as less than 1 year (average=28days). The largest one of 1km was induced by the M9.0 as M5.9 in 2011. The 1km's aftershocks of the M5.9 increased dramatically so as to catch up with the advanced count of 1km's one. But, 10km counts had gone further far away. So, 1km curve has been following behind 1km curve recently. 

20km(orange)…The count is the 3rd. Since 1939 when 20km curve was overtaken by 10km curve, 20km curve has been following behind 20km curve. The greatest increase of 20km started since 2010 before the M9.0. Even the one year advanced start of the rapid increase against ones of 1km/10km, 20km couldn't catch up with them. The largest one of 20km is M5.7 in 1947. It seems there has been not enough stocked energy of 20km to increase rapidly as of M9.0 in 2011.   

30km(yellow green)…The count is the 4th. The first increase was between 1960-1972 after the longest silent term between 1919-1960. Then, there was the 2nd longest silent term between 1972-2006.  After it, the silent terms were almost 4 or 5 years. The largest one of 30km is M4.7 in 1966.

40km(green)…The count is the 5th as same as 210km. But, there has been only 2 earthquakes of 40km as M4.4/M3.5.  

others…There is only each 1 time occurrence of 160km/190km/200km.