Counts of occurrence per depth in 渡島・檜山地方

Counts of occurrence per depth in 渡島・檜山地方 (Oshima,Hiyama region) is shown as below graph,

1km's count was the most one before M't Usu's eruption in 2000. After it, 10km's one becomes the most. It was occurred after the longest silent term (almost seven years) of 1km earthquakes. 10km's curve increased also by it, and there had been increased between 1995/11-2000/3. The increase of 10km seems to be occurred by M6.3 (20km) in 1993/8. Addition to it, M6.3 in 1993 may be occurred M6.1 (120km) in 1992. They had performed one chain reaction. Long silent terms were often found on the curves of shallow depths like as in 1km/10km/20km especially, and the rapid increase of the counts are occurred after them with high accuracy. In curves of deeper ones, the interval themselves are long in general.  So, there should be difficult to be found out the longer silent term than it.   

Counts of occurrence per depth in 石狩・空知・後志地方

Counts of occurrence per depth in 石狩・空知・後志地方 (redefined rectangle area of Ishikari,Sorachi,Shiribetsu region) is shown as below graph,

Before M6.7 (1km) in 1947, there was earthquake swarm of unknown details in Jan/1944. After M6.7 and the aftershock, log of the counts of 1km occurrence is linear against the date.Before M6.7 of 40km in 2018, there was earthquake swarm of 30km in Jul/2017. There was long quiet period of 40km between 1947-2018 also. In 2017, the count of 30km preceded it of 20km.    
 

Counts of occurrence per depth

In 胆振地方 just before M6.7 in 2018/9/6, Distribution of Depth (brown line) was as below,

After M6.7, the new peaks has grown up around 30-40km depth mainly. Before M6.7, there were the even peaks of 30km/130km. By M6.7, the peak of deep area has been shifted to shallow area. M6.7's epicenter was in 40km. If the epicenter were shallower more, the curve might have become more simple like as trapezoid with downhill in 三陸沖. The even peaks of 30km/130km seems to be the trigger of avalanche from the deep area to shallow area.

To make clear the relationship among the count changes per depth as  time sequence, I tried making the graph of Counts of occurrence per depth for the data in 胆振地方 as below,

Note : There are not all data of each depth. Some depth data are omitted.

Intersections among the lines between of the different depths seem to be the changing points of the pattern of the count curves per depth. Counts of 22 times of 4 lines of 20km(orange)/30km(yellow green)/40km(green)/130km(gray) are crossed in narrow area around the time of M7.6. Towards Year 2000, there was the first jump of 20km curve, the 2nd jump of 10km, and 3rd jump of 1km. The jumps had moved to deeper area to shallower area. The close-sets between 2 lines seem to becoming the changing patterns as like circled points. 

So, this graph may be useful for the prediction of the sudden increasing of counts (it may sometimes mean great earthquakes with many aftershocks). The long blank times until the next occurrence can be checked in the graph also. 

In 三陸沖, the graph of counts of occurrence per depth is as below,

The graph is more simple because of less depths.

Counts of 1km(red)/10km(yellow) have been overtaking and being overtaken. After jumping up, the line becomes flat, or tilted straight lines.The previous small jumping up were caused the next change in the other lines.