Mw 8.5-9.0 Offshore Lisbon, Portugal
updated 8 August 2021 UTC

On 1 November 1755 a great earthquake occurred offshore Lisbon, Portugal. The seismic event occurred at 09:40 local time and had an estimated moment magnitude (Mw) between 8.5 and 9.0.

Three planetary alignments from 28 to 31 October preceded the earthquake, most notably Sun-Mercury-Saturn on the 28th and Mercury-Sun-Neptune on the 31st. Lunar geometry does not seem overly critical at first. However, the Moon lined up with Saturn hours before Saturn lined up with the Sun and Mercury. In a very similar fashion, the Moon lined up with Neptune just hours after Neptune lined up with Mercury and the Sun. Apart from this specific geometry, it requires a very critical amount of fault stress for a rupture of this size to occur, which only happens every few to several hundred years at these kind of subduction zones.

Moon-Earth-Saturn        1755-10-27, 15:29:41  296°28'27"
Venus-Sun-Earth          1755-10-28,  2:47:38   37°47'52"
Sun-Mercury-Saturn       1755-10-28, 10:30:28  302°05'33"
Earth-Moon-Neptune       1755-10-29,  1:01:52  134°18'09"
Mercury-Sun-Neptune      1755-10-31, 13:19:14  132°26'03"

Sun:     Mercury-Earth   1755-10-31,  1:26:37   90°00'00"
Sun:     Mercury-Venus   1755-11-01,  0:37:24   90°00'00"
SSGI chart
SSGI depiction of planetary (PG) and lunar (LG) geometry


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