Counts of occurrence per depth in 岩手県沿岸北部

 Counts of occurrence per depth in 岩手県内陸北部（Northern inland of Iwate Pref. ）  is shown as below graph, 

As 20km curve has overtook 1km curve, shallow depths are top group of the counts. On the other hand, 20km curve is under 70km-100km curves. About magnitudes, M6.8 of 110km in 2008 is the greatest one of all depths. Such reversal status seems to be the energy charging mode. The stocked energy may be released huge earthquakes of shallow area as the open end with lots of aftershocks like as domino toppling.

 

• 1km (red)…The count is the 2nd. There was the longest silent term between 1988 - 1998. About 2 months later, M6.2 of 10km was occurred and brought out the rapid increase of 1km as the aftershocks. But, the increase of 10km had more aftershocks. The largest earthquake of 1km is M5.4 in 1927.
• 10km(yellow)…The count is the 1st. After becoming the 2nd by overtaking 80km, there was the rapid increase until 1963. Then, the silent terms became longer suddenly. During it, 80km curve caught up with 10km curve. But, back to back, the 80km curve had the longer silent terms. So, 10km curve became the 2nd again and the silent terms became shorter and shorter. Since May / 1998, the rapid increase began. They led to M6.2 of 10km in Sep/1998, and many aftershocks. On the way overtaking the 1km curve, the rapid increase is continuing still now. The longest silent term is between 1968 - 1982. The largest earthquake of 10km is M6.2 in 1998 (It was M5.0 in 1986 before M6.2).
• 80km(navy) …The count is the 3rd. Except the terms overtaken by 10km curve, 80km kept the 2nd. The largest earthquake of 80km is M4.9 in 2013.
• 90km(brown) …The count is the 4th. 90km is following behind 80km curve. But, it couldn't have caught up with 80km curve still. The largest earthquake of 90km is M5.9 in 1955.
• 70km(purple)…The count is the 5th. 70km is following behind 90km curve. But, it couldn't have caught up with 90km curve still. (It means 80km > 90km> 70km anytime.) The largest earthquake of 70km is M5.0 in 1936. 
• 100km(gray)…The count is the 6th. There is the 2nd longest silent term between 1919 - 1933. After M5.9 of 90km in 1955, 100km curve overtook 20km curve temporally. But, 20km curve overtook 100km, and kept the order until 2007. Finally, 100km curve has overtaken 20km curve at this moment. The largest earthquake of 100km is M5.2 in 1956.
• 20km(orange)…The count is the 7th.  As above, 20km curve and 100km curve was going back and forth. The largest earthquake of 20km is M5.0 in 1962.
• 110km(gray)…The count is the 8th as same as 120km. The largest earthquake of 110km is M6.8 in 2008. The M6.8 is also the greatest one of all depths.
• Others…omitted.