Counts of occurrence per depth in 埼玉県南部

Counts of occurrence per depth in 埼玉県南部(South Saitama Pref.)  is shown as below graph,

50km curve's increase is remarkable. 40km/60km curves are following. On the other hand, the shallow depths of 1km-20km are ranked low. As the greatest one of all depths is M6.3 of 60km, more occurrence may become more in general. But, like as M6.9 of 埼玉県北部(North Saitama Pref.) in 1931, great earthquakes may have the tendency in shallow depths. 

• 50km (light blue)…The count is the 1st. The steep slope is continuing still now. The longest silent term is between 1919-1923. The largest one of 50km is M5.8 in 1974.
• 40km (green)…The count is the 2nd. 40km curve was following behind 50km curve until 1980. There was the longest silent term of 40km between 1980 - 1996. By the long term, 40km curve became far from 50km curve and was overtaken by 60km curve. After it, the silent terms became shorter. In result, 40km curve overtook 60km curve in 2018. The largest one of 40km is M5.5 in 2016.
• 60km(blue)… The count is the 3rd. 60km curve was following behind 50km curve until 1998. During the longest silent term of 50km between 1990-1993, 60km became close to 50km curve. In stead of the end of the longest term of 50km, 50km curve's slope became steeper and 60km slope became gentle. The largest one of 60km is M6.3 in 1931. The M6.3 is also the greatest one of all depths. 
• 20km(orange)… The count is the 4th. There was the rapid increase of 20km in 1931. It was caused by M6.9 of 埼玉県北部(North Saitama Pref.) in 1931 as the aftershocks. The triple junction among 10km/20km/30km curves was occurred just after the M6.9 occurrence. After the rapid increase of 20km, the silent terms became shorter and the slope of 20km became gentle. The largest one of 20km is M5.5 in 1931. The M6.9 in 1931 was outside of this area.
• 70km(purple)… The count is the 5th. 70km curve was following behind 60km curve. The largest one of 70km is M6.1 in 1968.
• 90km(brown)… The count is the 6th. 90km curve was following behind 70km curve. The difference of counts of them has been becoming smaller. The largest one of 90km is M5.4 in 1965. 
• 80km(navy)… The count is the 7th. 80km curve had gone back-and-forth. But, there was the longest silent term of 80km between 1980-1995. In result, 90km curve had left from 80km curve. After the long terms, they became shorter again. Especially, after M9.0 Great East Japan Earthquake, the increase of 80km stood out in 2011. The largest one of 80km is M5.4 in 1980.  
• 1km(red)… The count is the 8th. After the M6.9 of 埼玉県北部(North Saitama Pref.) in 1931, the rank became the 1st-2nd temporally as same as 20km. But, the silent terms of 1km became longer. The longest silent term has been extending since 1983. The largest one of 1km is M4.6 in 1921.  
• 30km(yellow green)… The count is the 9th. After the M6.9 in 1931, there was the rapid increase. But, the rank became the 6th-7th. During the longest silent term between 1974-2009, 30km curve was overtaken by 30km curve. Furthermore, 2 years later the longest term of 30km, 30km curve was overtaken by 80km curve increased by the M9.0 in 2011. The largest one of 30km is M5.5 in 1931. 
• 10km(yellow)… The count is the 10th. After the M6.9 in 1931, there was the rapid increase. The rank became the 7th temporally more than 30km. But, the slope of 10km curve was very gentle. The rank has gone down until the 10th. The largest one of 10km is M4.8 in 1963. 
• others… omitted.