Counts of occurrence per depth in 釧路地方北部

Counts of occurrence per depth in 釧路地方北部 (North Kushiro region) is shown as below graph, 

1km (red)…This count of the earthquakes is the 1st one. There was the longest silent term between 1967-2002 (35 years). After it, there was a rapid increase of the count and 5 years silent term. Then the count is still increasing with high frequency. On the way, the curve have overtaken 10km. The max magnitude is M6.1 in 1938.

10km(yellow)…This count is the 2nd as overtaken by 1km when there was the longest silent term between 1988-2015 (27 years). The max magnitude is M6.5 in 1967. Before it, there was a rapid increase after M6.3 in 1959. M6.5 is the largest one of all depths also. 

20km(orange)…This count is the 3rd. The curve was following 10km with the rapid increase in 1959. But, there is no additional occurrence of 20km after M3.7 in 1971. The max magnitude is M5.6 in 1956.

30km(yellow green)…This count is the 4th. The latest occurrence was in 1968 (the magnitude was unknown). The max magnitude is M6.1 in 1959 as same as 1km. So, it seems there has been enough energy to grow up the count. But, the count is in the longest silent term since 1968 (57 years and more).

40km-80km … No occurrence.

90km(brown)… Only once occurrence in 1929 as unknown details (no magnitude data).

110km/130km/140km/150km…New comers since 1998. The max magnitude of them are only M3.5-M4.4. The counts are only 1-3 times.