Counts of occurrence per depth in 福島県中通り

Counts of occurrence per depth in 福島県中通り（Nakadori area of Fukushima Pref.）is shown as below graph, 

10km/1km/20km curves jumped up by M9.0 Great East Japan Earthquake far from this area. The total counts of 1km-20km&90km&80km account for about 92% of all occurrences in this area. The rapid increase by M5.7 of 10km in 2010 was occurred on the twin junction of 10km/90km in the previous year of M9.0. The M5.7 seems to be one of the sign of the M9.0 in 2011 as same as the long silent terms of 1km/20km/40km/50km. The M5.7 of 10km in 2011 led to M6.1&M7.0 of 10km in 2011. The M7.0 of 10km is the greatest magnitude of all depths in this area.

  

1km (red)…The count is the 2nd. There was the rapid increase by M5.7 of 1km in 1924. The next rapid increase was in 1938. It was caused by M7.5 off the coast of Fukushima Pref. (outside of this area). These rapid increases made the rank of the 1st keep for long time until 2010. Then, the silent terms became longer gradually. The longest silent term was occurred between 1984-2005.  M9.0 Great East Japan Earthquake was occurred after 5 years silent term between 2005-2010. The M9.0 induced both M7.0 of 10km and the many aftershocks of 10km/1km. Because of less aftershocks of 1km than 10km, the rank went down to the 2nd. The largest magnitude of 1km is M5.7 in 1924.

10km (yellow)…The count is the 1st. Before the M9.0, the curve was located near 90km curve or so on. 1 years ago of the M9.0, M5.7 was occurred in 2011 on the twin junction of 10km/90km. There was the rapid increase in 2010 by M5.7 before the further rapid increase by M9.0 in Mar/2011. It led to M7.0 of 10km in Apr/2011. The 7.0 is the greatest one of all depths. 

20km(orange)…The count is the 3rd. Before the M9.0, 20km ranked the 6th or so on. The longest silent term is between 1960-1981. The 2nd and 3rd were occurred before the M9.0 in 2011. The 2nd is between 1989-1999, and the 3rd is between 2000 - 2011 until the next day of the M9.0. M5.7 of 20km in 2013 was induced by the M9.0. By the M5.7, 20km was increased rapidly in 2013. According withe the rapid increase, 20km was close to the twin junction of 10km/90km in 2011 nearby. The largest magnitude of 20km is M6.5 in 1922. 

90km(brown)…The count is the 4th. The 90km curve has been increased almost constantly. The curve was overtaken by 10km/20km aftershocks of the M9.0. But, 90km curve is closing to 20km recently. The largest magnitude of 90km is M5.4 in 2022.  

80km(navy)…The count is the 5th. 80km curve was following behind 90km curve. The largest magnitude of 90km is M5.7 in 1957.  

others… Remaining counts except the 1st-5th are only 8%.