Counts of occurrence per depth in 群馬県北部

Counts of occurrence per depth in 群馬県北部（North Gunma Pref.）is shown as below graph,

The counts of 1km-20km is occupied 96%. Both 1km and 10km curves has been overtaking each other since 2000 including the rapid increases as the aftershocks of M9.0 Great East Japan Earthquake. 20km curve stopped after the longest silent term between 2003-2023. 

•  1km (red)…The count is the 1st.  1km curve had kept the 1st rank until 2000. There was the longest silent term between 1989-1999. During it, 1km curve was overtaken by 10km curve once. But, the rapid increase of 1km was caused by M5.9 of 1km as the one of the aftershocks of M9.0 Great East Japan Earthquake. As the increase of 1km was more than the one of 10km, 1km curve became the 1st rank. 2 years later, 1km curve increased again by M6.3 before being caught by 10km curve. Both the M5.9 and the M6.3 of 1km were the largest one at that time. The M6.3 is the greatest one of all depths.
• 10km (yellow)…The count is the 2nd. There was the longest silent term between 1919-1933. The 5th one（the 2nd at that time）was between 1937-1941 after 4 years. Furthermore, the 2nd one continued between 1942-1949 after 1 year. After it, the silent term became shorter until 1970.  Then, there were the 4th and the 3rd longest silent terms between 1970-1974 / 1974-1981. After them, the curve slope became steeper until 2011. During it, 10km curve overtook 1km as wrote above. In 2011, there was the rapid increase as the ones of aftershocks of the M9.0. But, the increase of 10km was less than 1km. The largest one of 10km is M5.2 in 2018.
• 20km (orange)…The count is the 3rd. 20km curve was following behind 10km curve until 1988. Then, the silent terms became longer. After the longest silent term between 2003-2023, there has been no earthquake. The largest one of 10km is M4.9 in 1975. 
• others…The sum of counts among the 1km-20km is occupied 96%. Others are omitted.