Mw 8.1 Bio-Bio, Chile
updated 28 August 2021

On 21 May 1960 a great earthquake occurred in Bio-Bio, Chile at a depth of 25 km. The seismic event occurred at 10:02:57 UTC and had an estimated moment magnitude (Mw) 8.1.

A series of four planetary alignments occurred from the 17th to the 22nd, most notably Venus-Sun-Neptune on the 20th and Mars-Mercury-Uranus on the 21st. The great earthquake in Bio-Bio, Chile was the first in a series of major earthquakes in the region, peaking magnitude 9.5 on the 22nd, thus far the largest earthquake on record (since recording began in 1901). A lunar peak on the 20th, that reached index 13 practically converged with the Venus-Sun-Neptune alignment, but peaked slightly afterwards, after which the earthquake occurred. The Mars-Mercury-Uranus alignment later on the same day preceded three additional large tremors on the 22nd. Lunar geometry was already critical on the 17th, especially with Mars and Jupiter. The lunar peak on the 20th involved a conjunction with Mars. Two weeks later, after the opposition, another major earthquake occurred in Aisen, Chile, also involving critical planetary geometry.

Mercury-Sun-Earth         1960-05-17, 15:04:11  237°15'07"
Venus-Sun-Neptune         1960-05-20, 12:29:24  218°27'30"
Mars-Mercury-Uranus       1960-05-21, 15:05:56  141°42'49"
Mercury-Sun-Jupiter       1960-05-22,  8:32:19  266°57'27"

Earth:   Moon-Jupiter     1960-05-17,  4:30:34   45°00'00"
Earth:   Moon-Mars        1960-05-17,  8:09:02   45°00'00"

Earth-Moon-Mars           1960-05-20, 22:49:12    7°53'36"

SSGI chart
SSGI depiction of planetary (PG) and lunar (LG) geometry