August 27, 1810 Earthquake: Loreto, Baja California, Mexico

The earthquake was destructive in Loreto and was followed by a tsunami. The damage area likely included San Ignacio, 200 km northwest of Loreto, and rockfalls were described from Loreto all along the main gulf escarpment to La Paz, 230 km to the south. The earthquake source was most likely the Farallon transform fault in the Gulf of California.

The mainshock was felt in Loreto 27 August 1810 at 8 a.m. The major buildings such as the town hall, the two arsenals, the guard house, the forge, and the house of the lieutenant were destroyed. The church, a massive stone-and-mortar construction (Crosby, 2007), was shifted from its foundation and was in danger of collapse. Frequent aftershocks lasted at least until 2 September 1810. Based on reports received by Goycoechea, the felt area included the Los Cabos region, the southernmost part of the peninsula, and reached at least up to 170 km north of Loreto. The earthquake shifted and fissured the ground between the town and the seashore and opened several holes from which water emanated. There were landslides along the entire mountain range between Loreto and the harbor of La Paz, a distance of 230 km.

Excerpt of report by Goycoechea, translated:"The immediate past 27 August, at 5:20 a.m., an earthquake occurred in this presidio. It destroyed its major buildings such as the town hall, the two arsenals, the guard house, the forge, and the house of the lieutenant. Several other buildings housing the families of the soldiers and sailors were less damaged because of being small and low. However, there were no casualties, since everybody was sleeping outside because of the excessive heat at that time of the year." (Supplement #4)

The magnitude of the A.D. 1810 earthquake can be estimated as Mw 7:4 (+/- 0.2) from the rupture length-magnitude scaling relationship for continental strike-slip faults by Wesnousky (2008), based on the assumption that the A.D. 1810 earthquake ruptured the entire Farallon transform fault.

(all above from reference #12400)