August 27, 1810 Tsunami: Mexico

Reference #12400:

Goycoechea also reports several tsunami waves 1 hr after the mainshock. The waves approached with such a speed that the habitants thought they would be inundated by the sea without having a chance to run to higher ground. A brigantine, firmly tied up with four anchors at Puerto Escondido, a natural harbor 28 km south of Loreto, did not stay in place because of the strong sea, and the vessel was almost stranded.

As for the A.D. 1810 earthquake, the reported tsunami points to a marine source. This event likely originated on the Farallon transform fault, ∼125 km long, which links the Carmen and Farallon extensional segments of the plate boundary ∼90 km east of Loreto. The tsunami may imply a vertical component in the motion of the ocean floor or else it possibly was caused by a submarine landslide. However, given the arrival time of the tsunami waves, ∼1 hr after the mainshock, it is unlikely that the tsunami was triggered by the mainshock.

Excerpt of report by Goycoechea, translated:Up to 150 varas [125.7 m] from the seashore, nearly up to the town hall, the earthquake shifted and fissured the ground and opened several holes from which water emanated. There were landslides along the entire mountain range between here and the harbor of La Paz, which caused much noise and crash. After one hour, the sea was several times in motion. It moved outside the shoreline with such a speed that for a moment we thought to become buried by it (without giving us a chance to run to higher ground to avoid becoming a victim), unless, as it was noted, the furious waves moved towards the island located opposite this presidio, which is called del Carmen. (Supplement 4)

Reference #12401:

the associated tsunami was disproportionally large if compared with the earthquake intensity (IX) and approximate magnitude (7.4Mw; Suter 2018), fault style, and the relatively late tsunami arrival, i.e. an hour after the earthquake, suggesting that a submarine landslide, triggered by this earthquake, was the suspect source for the Loreto tsunami.

The historical description of the tsunami suggests localized large waves and approximately ‘‘40 leagues (ca. 5 km) inundation distance'', which does not agree with the 27 August 1810 earthquake as the direct source mechanism.

historical accounts indicate that ‘‘the tsunami flooded 5 km inland in Tembabichi''.

[...]the earthquake-triggered ground motion that is destabilizing and produces a tsunamigenic submarine landslide.

‘‘…they saw the vast movements that the sea made and they subsequently learned that between this garrison and the port of La Paz in an inlet that they call de Tembabichi (alternatively Tembabiche) the sea went out more than a league; it destroyed the piers and left for the vessels a good anchorage, and at other sites made less damage''.