Counts of occurrence per depth in 胆振地方

Counts of occurrence per depth in 胆振地方 (Iburi 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 2nd one. But, the max Magnitude is M5.6 in 2014. The max of all depths in this area is M6.7 of 40km in 2018 (named "The 2018 Hokkaido Eastern Iburi Earthquake"). But, there were not rapid increase of 1km/10km, but of 30km/40km. There were 2 major rapid increases of 1km/10km. One was in Jan/1944 related with the growth of M't Showa-shinzan, which is very famous as newborn volcano in Showa era. As the earthquakes were caused by volcano activity, most of the Magnitudes were unknown, and no rapid increase of other depth like as 10km or so on.  The another rapid increase was occurred in Mar/2003. It was caused by the volcano activity of M't Usu eruption. After 2 rapid increases, the increase of 1km count becomes very slow. 
  
• 10km (yellow)…The count has become the 1st one after M't Usu eruption in May/2003. These earthquakes were occurred as the advance activity of the eruption. The max Magnitude was M4.9 as one of the volcanic earthquakes of M't Usu in Apr/2000.
• 30km (Yellow Green)… The count is the 3rd. The rapid increase was occurred continuously. The 1st one was caused by M5.1 of 30km in Jul/2017. The second one was occurred just after the M6.7 of 40km. By the 1st increase , the count of 30km had approached to the count of 21 of 130km. The below graph is the count per depth in 胆振地方.Orange line shows the counts just before M6.7, and Blue one shows the current one.

   By 1st rapid increase of 30km, the count had caught up with the one of 130km as 21 counts. In result of M6.7 in 2018, the counts of 20km-30km has jumped up (especially 30km). This change seems to be the adjustment against the concave of curve around 30km's peak caused by the rising tail around 130km's one. The touch up with the count to 130km may have become the trigger of M6.7 of 40km for the adjustment.

 

 The next graph shows the comparison of the counts  before and after M9.0 in 2011. The curve shapes may be the final ones. It seems Avalanche caused by unbalance potectial energy makes the surface flat. (though the energy from deeper to shallower as a tendency).

 

 

 

• 40km (Green)… The count is the 5th. The below list shows the counts of 20km/30km/40km/130km around count of 22. Red font shows the data of M6.7 of 40km in 2018/9/9. As wrote above, the same count may be the trigger of M6.7 of 40km. Then the count of 40km had the rapid from 5 to 21 almost in 1 hour. The count of 20km reached from 18 to 21 about 3days later. 

• 20km (Orange)… The count is the 5th. The curve of 130km is approaching. The catch up with them might become some trigger of the increase of 20km.
• 130km (gray) … The count is the 6th. It is still increasing continuously.