Counts of occurrence per depth in 東京都

Counts of occurrence per depth MD-T chart in 東京都 (Tokyo）is shown as below graph,  

1km curve increased rapidly by far from others. But, after it , the silent terms became longer and longer. The increase has stopped since 1981. During the stop, 20km/30km curve are increasing instead of 1km. 40km-80km curves are also increasing. But, the slopes are far gentler than one's of 20km/30km. 

20km (orange)…The count is the 1st. There was the rapid increase by M7.9 Great Est Earthquake in 1923. 60km curve has been increasing steadily. The largest one of 60km is M5.7 in 1980. The next major rapid increase was caused by M5.5 in 1976. The 3rd major occurrence was caused by M9.0 Great East Japan in 2011. By the 3rd increase, 20km curve overtook 1km curve. The largest one of 20km is M6.0 in 1983. The M6.0 was occurred 2 years later of the last occurrence of 1km.      

1km (red)…The count is the 2nd. There was the rapid increase by the M7.9 in 1923, and the count rank became the 1st. Then, the silent terms became longer and longer. The 2nd longest silent term was between 1961-1973, and now, the 1st longest silent term is extending since 1981. The largest one of 1km is M6.2 in 1923. The last count of 1km was 225 times. The same count of 20km was occurred in Mar/2011 only 4 days later. It seems the count might have suggested the occurrence of the M9.0 in Mar/2011. 

30km（yellow green）…The count is the 3rd. 30km curve was following 20km curve. But, the major rapid increase timings were different from one's of 20km curve. The major increases were both in 1923/1988. The one in 1988 was caused by M5.6. The M5.6 is the largest one of 30km. As these increases were far less than one's of 20km. The count of 30km is only half of one of 1km.

40km(green)…The count is the 4th. After the rapid increase of 40km in 1923, 40km curve continued steadily, and the count became the 2nd in 1944. But, the silent term became longer. The longest silent term was between 1946-1953. After it, there has been no major increase. The count of 40km is only half of one of 30km. But, M6.3 of 40km in 1929 is the greatest one of all depths as same as M6.3s of 50km/60km. 　  

60km(blue)… The count is the 5th. 60km curve was accelerated by 2 times of M6.3 in 1926/1931. 60km was following behind 50km curve until the catching up with it. During it, 60km curve almost overlapped with 70km curve. But, after it, 60km closed with 50km. M6.3 of 60km is the greatest one of all depths as same as M6.3 of 40km/50km.

50km(light blue)… The count is the 6th. 50km curve was following behind 40km curve. But, after the acceleration by M6.3 of 50km in 1923, there has been no major rapid increase. The M6.3 is the greatest one of all depths as same as ones of 40km / 60km. The count is almost same as ones of 60km/10km now.

10km(yellow)…The count is the 7th. Until 1940, the count was the 2nd or so on. But, as there has been no major rapid increase after it, the counts become almost same as ones of 60km/50km. The largest one of 10km is M5.2 in 1923. 

others …omitted.