Deep distribution of the hypocenters of earthquakes of the Kuril region
This work is aimed at a comparative analysis of earthquake distribution by depth and magnitude in the four study subregions of the Kuil Islands and numerical determination of the Hopt value for these subregions. The Hopt value is the depth boundary which divides seismic events in every study subregion into two non-overlapping subsets. The seismic events of the first subset are distributed non-uniformly during the year, while the distribution of seismic events of the second subset is uniform. The analysis shows that the boundary position between these two subsets depends on the character of hypocenter distribution over the depth and on the magnitude values. The optimal threshold value of the depth calculated by statistical method varies from 40 to 80 km for the Southern, Middle Kuriles and Hokkaido Island and from 60 to 100 km for the Northern Kuriles. A comparison was made of the statistical analysis results with the earthquake distribution over depth according to the basic Kuril catalog.