Earthquake Private Laboratory in Japan

Tuesday, May 13, 2025

Counts of occurrence per depth in 北海道南西沖

Counts of occurrence per depth in 北海道南西沖 (Southwest offshore Hokkaido region) is shown as below graph,

According with the wider domino effect of depth range, the magnitudes become greater from M6.1 in 1950, M7.1 in 1982, and M8.3 in 1993.

10km (yellow)…This count of the earthquakes is the 1st one. 10km&20km curves has chased each other back and forth. Recently, 10km is more than 20km. There was a rapid increase of 10km caused by M6.1 in 1950 after the longest silent term between 1929 - 1950. The 2nd step up was caused by M7.1 in 1983 after the 2nd longest silent term between 1967 - 1983. The 3rd step up was caused by M7.8 of 40km in 1993. The rapid increase of 10km after M7.8 was delayed from the ones of 40km/30km/20km/1km. It seems to show the domino effect of earthquakes of M7.8 should have been carried over from the epicenter of 40km to shallower depth. The max magnitude of 10km is M7.1 in 1983.

20km(orange)…This count was the 2nd overtaken by 10km recently. The 1st step up was caused by M6.1 of 10km in 1950 delayed from 10km after the 2nd longest silent term between 1930 - 1953 of 20km. The 2nd step up was caused by M7.1 of 10km in 1983 after the longest silent term between 1966 - 1983. The 3rd step up was was caused by M7.8 in 1993. M6.3 of 20km was also caused M7.8. This M6.3 is the max magnitude of 20km.

30km(light green)…This count was the 3rd. After the longest silent term between 1942 - 1966, there were 2 long silent terms between 1966 - 1977 / 1977-1983. After them, there was the rapid increase of 30km in 1983 was caused by M7.1 of 10km. The 2nd increase was caused by M7.8 of 40km in 1993. In result, 30km has overtaken 1km. The max magnitude of 30km is M6.0 in 1983 caused by M7.8.

40km(green)…This count was the 4th. After the longest silent term between 1933 - 1967 , M7.8 was occurred in 1993 as the end period of 2nd longest silent term since 1967. The M7.8 in 1993 became the origin of domino effect from 40km to 1km. M7.1 of 10km in 1983 had the smaller domino effect from 30km to 1km. The difference from M7.1 to M7.8 seems to be the difference of the depth ranges, not only the one of the length of fault (The deeper cut should have the wider aperture area). M6.1 of 10km in 1950 had the further smaller domino effect from 10km to 1km.

50km(light blue)…This count was the 5th. After long silent terms, only 2 earthquakes were occurred just after M7.8 of 40km in 1993 as 4th & 5th of the total count of 50km additionally.

Others … M6.4s were occurred of 240km in 1981 / of 250km in 1996 as outstanding ones.