Counts of occurrence per depth in 日高地方

Counts of occurrence per depth in 日高地方 (Hidaka region) is shown as below graph,

note : There are not included of all depths to avoid too complicated curves. 

• 1km (red)…This count of the earthquakes is the 1st one. There was a rapid increase of the count by M6.8 of 30km in 1931/M6.9 of 70km in 1932. After the pace down gradually, there was a speed up by M6.8 in 1944. This M6.8 is the max magnitude of 1km. There was a long silent term of 1km between 1964-1968 (4 years). Before 2 months ago of the end of the term, M6.8 of 50km was occurred in Sep/1968. 2 years later, M6.7 of 60km was occurred also. These earthquakes seem to have accelerated the count of 1km. The increase might be stopped by 2 earthquakes of M6.9 of 130km in 1981/M7.1 of 40km in 1982. The 2nd longest silent term was occurred between 1982-1995. The longest one continued to occur between 1995-2011. As described above, M7.1 of 40km is the max magnitude in this area. After the other long silent term between 2011-2018, M6.7 of 40km was occurred in Sep/2018 as just before the end of it. Since then, the frequency has increased a little bit more.
• 60km(blue)…This count of the earthquakes is the 2nd one. It is far more than them of 10km/20km. Such reversal status may become the trigger of avalanche phenomenon to release the unbalance of the potential energy. The count seems to accelerate the count when it takeovers them of 20km/40km/50km. The max magnitude is M6.7 in Jan/1970.    
  
• 70km(purple)…This count of the earthquakes is the 3rd one. The curve overtook 50km/60km. But, It has been overtaken by 60km at last. The max magnitude is M6.9 in Nov/1932.  
• 50km(light blue)…This count of the earthquakes is the 4th one. Though the curve was overlapped with it of 40km, it just barely succeed in keeping the count raking as 4th. The max magnitude is M6.8 in Sep/1968.     
  
• 40km(green)/30km(yellow green)…The curve 40km(green) has almost been keeping higher rank than 30km's one. There has been 3 major rapid increases in common with 40km/30km. The 1st was M6.7 of 60km in 1970, the 2nd was M7.1 of 40km in 1982, and the 3rd was M6.7 of 40km in 2018. M7.1 is the max Magnitude of 40km. On the other hand, the max magnitude of 30km is M6.8 in 1931 (far older than 3 major increases). The counts of 50km/40km/30km are in reverse status against the natural one with low potential energy. Further more, the difference of them are few. It may show there should be a big turning the table in future.  
• 10km(yellow)…This count of the earthquakes is the 9th (lowest in 1km-90km). It seems there should be huge stress stocking around there.
• Others…100km-120km's curves are still extending actively also.  
  

In wide range depths, the earthquake occurrences are very active. So, we should need to watch them carefully.