Counts of occurrence per depth in 択捉島付近

 Counts of occurrence per depth in 択捉島付近(Etorofu Island)  is shown as below graph, 

Only 1km stands out from others. On the other hand, 100km and deeper ones are high ranks of the counts. Especially, 100km stands out from others except 1km.   Such case is rare. In general, deeper ones are less than shallow ones. It seems  there could be around M7 of 40km or 30km (or both) in several years. Recent curves have steeper slopes.    

1km(red)…This count of the earthquakes is the 1st. The longest silent term was between 1937-1954. 4 years later, M6.7 was occurred in 1958 (M6.7 is the greatest one of 1km). By this M6.7, the count increased rapidly.  After several steps, there was the 2nd longest silent term between 1989-2001. Just before the end of it, there was M6.9 of 30km in 2001. Since 2008, the slope becomes steep. The the largest magnitude in this depth is M5.9 in 1979.   

100km(gray)…The count is the 2nd since M7.2 in 1978. The M7.2 is the greatest one of all depth. Then, the curve follows 1km still now. 5 depths of more than 100km are within top 10 of counts. The count of 100km is less than half of 1km. 

120km(gray)…The count is the 3rd. The the largest magnitude in this depth is M6.6 in 1945. The count of 100km is less than 1/3 of 1km. 

80km(navy)…The count is the 3rd as same as 120km. The the largest magnitude in this depth is M6.4 in 1962. 

90km(brown)…The count is the 5th. After M6.1 in 1938, there was the longest silent term between 1938-1978. About 6 months later, M7.2 of 100km was occurred in 1978. After several steps, there was the 3rd longest silent term between 1989 - 2003 (2nd was between 1919- 1938).  Before 2 years ago from the end of it, there was M6.9 of 30km in 2001.  Since 2011, the slope becomes steep. The largest magnitude in this depth is M6.1 in 1938. 

40km(green)…The count is the 5th as same as 90km. There was the 2nd longest silent term between 1939-1968. Then, the slope became steep. After M7.2 of 100km 1978, it became steeper. In 1982, M6.8 was occurred as the greatest one of 40km. Since the M6.8, there was the longest silent term between 1984 - 2021. It could be around M7 or so on in several years.

150km&160km(gray)…The count is the 5th as same as 90km/40km. The largest magnitude in this depth is M5.7 in 2002(150km)/M6.2 in 1985(160km). 

30km(light green)…The count is the 9th as same as 130km/140km. The count difference between 40km is only 4 times. The largest magnitude in this depth is M6.9 in 2001. 

130km&140km(gray)…The count is the 9th as same as 30km.  The largest magnitude in this depth is M5.7 in 1928(130km)/M6.3 in 1941(140km).  

others…omitted