Counts of occurrence per depth in 青森県・陸奥湾・津軽海峡

Counts of occurrence per depth in 青森県東方沖 (Eastern offshore of Aomori Pref.） is shown as below graph,

1km/10km account for two-thirds of the total. On the other hand, 70km and deeper accounts for 20% of the total. 90km/80km are the center of the deep area, and their epicenters are concentrated on both the east side and Eastern offshore of Aomori Pre except Simokita Peninsula. 

• 1km(red)…The count is the 1st. There were rapid increases between 1919-1984. The rapid increase in 1929-1930 was the greatest one (count as 41-65). Then, the silent terms became longer. The longest silent term of 1km was between 1993-2013. After that, the terms became shorter again. The largest one of 1km is M5.9 in 1955 (count as 307).
• 10km(yellow)…The count is the 2nd. There were 2 major rapid increases of 10km. The previous one was between 1978-1980 (count as 31-51). M5.8s (count as 31&32) in 1978 were the triggers of them. These M5.8s are the largest one of 1km. The following one was between 1995-1996 (count as 72-91). The steep slope of 10km curve is still continuing. 
• 90km(brown)…The count is the 3rd. The epicenters are concentrated on both the east side and Eastern offshore of Aomori Pre except Simokita Peninsula. The 1st longest silent term is between 1919-1938. The 3rd-5th ones are continuing between 1940-1958 (count as 3-6).  The 2nd one is between 1972-1980 (count as 21-22). Just after it, M5.7 occurred in 1980 (count as 23). The M5.7 is the largest one of 90km. The silent terms became shorter gradually. 
• 80km(navy)…The count is the 4th. As same as 90km, the epicenters are concentrated on both the east side and Eastern offshore of Aomori Pre except Simokita Peninsula. 80km curve was intertwined with 90km curve. The longest silent term is between 1919-1937 (count as 1-2).  The largest one of 80km is M4.9 in 1960 (count as 12).
• 20km(orange)…The count is the 5th. 20km curve was following behind 10km curve. After the longest silent term of 20km between 1953-1968 (count as 5-6), 20km curve was overtaken by 80km/90km curves. The largest one of 20km is M5.1 in 1953 (count as 5).
• 110km(gray)…The count is the 6th. During the 5th silent longest term of 110km between 1954-1964 (count as 10-11), 90km/80km curves overtook 110km curve. As same as 90km/80km, the epicenters are concentrated on both the east side and Eastern offshore of Aomori Pre except Simokita Peninsula. The largest one of 110km is M5.3 in 1921 (count as 2).
• 70km(purple)…The count is the 7th. 70km curve was intertwined with 90km/80km curves. But, after M6.6 of 70km in 1960(count as 14), the silent terms became longer gradually. During the 3rd longest silent term of 70km between 1971-1980 (count as 22-23), 70km started to be late from 90km/80km curves. The M6.6 of 70km in 1960 is the greatest one of all depths.
• 100km(gray)…The count is the 8th. 100km curve is following behind 90km curve. The largest one of 100km is M5.5 in 1960 (count as 7).
• others…omitted.