Mw 8.3 Rat Islands, Aleutian Islands
updated 4 June 2021 UTC

On 17 August 1906 a great earthquake occurred at the Rat Islands, Aleutian Islands at a depth of 110km. The seismic event occurred at 00:11:10 UTC and had an estimated moment magnitude (Mw) 8.3. It was the first of two great earthquakes on the 17th within 30 minutes.

In 1905 and 1906 the positions of Uranus and Neptune and also Jupiter made Earth to line with them in an in-between fashion which caused the Moon to make critical geometry with two gas giants on opposite sides within a few hours. All six M 7.8> earthquakes in 1906 occurred under these conditions.

Two planetary alignments occurred around 17 August 1906, but the one precedinig the earthquake on 12 August is not statistically know to cause this large seismic activity on its own. Indeed, a huge lunar peak on the 15th and 16th preceded the earthquake. Earth was closely aligned with Jupiter and Uranus and the Moon lined up with both of them within 4 hours. Later on the 16th the Moon also lined up with Neptune. But the Moon's alignments with Jupiter and Uranus within a few hours was a decisive factor. In addition, two WPG peaks reached index 8 before and during the lunar peak. The critical planetary geometry that also converged with the lunar peak, indicated by the red peak, involved Mercury's 90° angle with Earth and Venus. It's timing also made it a significant contributing factor.

Sun-Mercury-Earth        1906-08-12, 11:49:42  320°08'57"
Sun-Mercury-Saturn       1906-08-18,  4:22:59  342°21'39"

Earth-Moon-Jupiter       1906-08-15, 23:13:54   94°26'53"
Moon-Earth-Uranus        1906-08-16,  2:36:11  276°09'14"
Earth-Moon-Neptune       1906-08-16, 16:01:26  102°59'01"

Mercury: Venus-Earth      1906-08-15, 15:54:23   90°00'00"
SSGI chart
SSGI depiction of planetary (PG) and lunar (LG) geometry


This website is using cookies. Terms and conditions, Privacy Policy