Counts of occurrence per depth in 岩手県内陸南部

Counts of occurrence per depth in 岩手県内陸南部（Southern inland of Iwate Pref. ）  is shown as below graph,  

Just after M6.2 of 20km in 1970, 1km/10km/20km were occupied the top ranks of the 1st-3rd. But, after M7.1 of 70km on the triple junction among 70km / 80km / 60km in 2003, these rapid increases made the ranks jump up. As M7.2 of 10km in 2008 brought out the rapid increases of 10km/1km, they can keep the high ranks as the 1st/3rd. On the other hand, 20km ranked down from the 3rd to 6th.

• 1km (red)…The count is the 3rd. Long silent terms seem to make rapid increase be occurred, and they make the curve form as steps. The longest silent term was between 1996-2004, and M7.2 of 10km was occurred 4 years later as the greatest one of all depths. The largest earthquake of 1km is M5.1 in 1996. Before the M5.1, there were also 2 long silent terms of 3rd (2nd) / 6th (4th). (() was the rank at that time) .
• 10km(yellow)…The count is the 1st. There were 2 major rapid increases. One was the rapid increase by both foreshocks and aftershocks of M5.8 of 10km in 1996. The another was the one by M7.2 of 10km on triple junction among 60km-80km in 2008. The M7.2 is the greatest one of all depths, and the aftershocks made the counts rank up to the 1st by the aftershocks. 
• 70km (purple)…The count is the 2nd. Before M7.1 of 70km in 2003, the rank was the 3rd. But, the M7.1 made the rank jump overtaking 1km finally. The M7.1 was occurred on the triple junction among 60km/70km/80km (20km was also nearby). The largest earthquake of 70km is the M7.1 in 2003. 
• 80km (navy)…The count is the 4th. 80km curve was following 70km curve, and the rapid increase was occurred by M7.2 of 70km as same as 70km. But, almost always, 80km curve was located below 70km curve. The largest earthquake of 80km is the M5.3 in 1996.
• 60km (blue)…The count is the 5th. 60km curve was following 80km curve, and the rapid increase was occurred by M7.2 of 70km as same as 70km/80km. But, almost always, 60km curve was located below 80km curve. The largest earthquake of 60km is the M4.6 in 2018.
• 20km(orange)…The count is the 6th. But, the rank was the 3rd when there was the rapid increase by M6.2 of 20km in 1970. After the rapid increase, there was the 2nd longest silent term between 1973-1983. On addition to it,the 1st longest silent term was also occurred between 1994-2007. In result, 70km/80km/60km curves overtook 20km curve, and 90km is approaching within reach. The largest earthquake of 20km is the M6.2 in 1970.
• others…omitted.