Counts of occurrence per depth in 長野県南部

Counts of occurrence per depth in 長野県南部  (Southern Nagano Pref.) is shown as below graph,

The count of 10km is the 1st, and it is increasing steadily still now. As the greatest one of all depths, M6.8 of 1km occurred in 1984. Maybe because of 1km occurrence, the aftershocks occurred almost only 10km without 1km ones. 

• 10km (yellow)…The count is the 1st. There was the longest silent term of 10km between 1939-1947. Then, 10km curve was increasing almost gradually between 1952 - 1984 (count 15-51). After the 4th longest silent term of 10km between 1979-1984, there was a rapid increase by M6.8 of 1km in 1984. After the M6.8 of 1km, the count of 10km was accelerated, and overtook the one of 1km in 1995. After the overtaking, the count was accelerated more, and M5.6 of 10km as the 2nd scale occurred in 2017. Recently, the silent terms of 10km have been decreasing gradually. M6.2 of 10km in 1984 is the largest one. 
• 1km (red)…The count is the 2nd. The 5th longest silent term of 1km between 1951-1955 (count  56-57) was the 1st one at that time, and the silent terms became shorter after it. 1km curve changed the slope steeper between 1955-1969 (count 57-114). Then, the silent terms became longer. The 4th longest silent term of 1km occurred between 1990-1994. M6.8 of 1km occurred at the end of the 4th term. Even though the M6.8 of 1km in 1984 is the greatest one of all depths, there was almost no aftershocks of the M6.8 as 1km depth. Most of the aftershocks of the M6.8 in 1984 was induced as the rapid count increase of 10km between 53-84. The start count 53 of 10km was near to the start count of 1km's 5th longest silent term in 1951. 2 years later of the M6.8, there was the longest silent term between 1986-2005. More than 95% of 1km before it were with no magnitude data as "unknown details" or "unknown magnitude". They seem to be one of the sign of the M6.8 of 1km in 1984. After the M6.8 in 1984, there has been no one with no magnitude data yet. And the silent terms became longer gradually after the longest one. The 2nd longest silent term of 1km occurred between 2013-2018. The 2nd one seemed to be interrupted by M5.6 of 1km in 2017.    
• 20km (orange)…The count is the 3rd. 20km curve has been following behind 10km curve. But, 20km curve couldn't catch up even with 1km curve. The latest one was count 57, and the value has reached the 5th longest silent term of 1km between 1951-1955 (count  56-57) . So, 20km curve might go into a long silent term. The largest one of 20km is M4.8 in 1927.
• 50km (light blue)…The count is the 4th. 50km curve has been following behind 20km curve. The silent terms accelerated since 1998 as same as 10km after the overtaking 1km curve. The silent terms of 50km became longer once when becoming close to 40km curve. But, after overtaking 40km curve, they became shorter. The increase stopped in 2024. The largest one of 50km is M5.1 in 1981.
• 40km (green)…The count is the 4th. The 2nd longest silent term was between 1939-1959. 40km curve was caught up with by 20km curve around 1960s. Then, the silent terms became longer. Furthermore, there were the 3rd/1st silent term between 1972 - 1988/1988-2015. The latest one was in 2021. The largest one of 40km is M5.1 in 1919.
• 30km (green)…The count is the 5th. 30km increased steadily, and overtook 40km once in 1958. But, after it, the silent terms became longer rapidly. The latest one was in 2017. The largest one of 30km is M5.3 in 1926.
• 60km (blue)…The count is the 6th. The longest silent term is between 1919-1993. Then, there have been only 5 occurrences since 1993. The largest one of 60km is M5.1 in 1981.
• others⋯ As remarkable ones of others, there were M6.6 of 250km/M6.0 of 260km.