8 December 1812 M6.9

San Juan Capistrano: A description of the earthquake at San Juan Capistrano is given by Engelhardt (1922), from the writings of Fray Suner and Fray Barona who were at that mission: "On the eighth day of this month (December) consecrated to the Most Pure Conception of the Most Holy Virgin, a terrible earthquake occurred while the first holy Mass was be celebrated, which was about (the figure is torn out) in the morning. In a moment, it completely destroyed the new church built of masonry (cal y canto). It required more than nine years to construct it, but it lasted no more than six years and three months to the day; for it was blessed on September 8, 1806. The tower tottered twice. At the second shock it fell on the portal and bore this down, causing the concrete roof to cave in as far as the transept exclusively. Forty Indians, thirty-eight adults and two children, were buried beneath the reins, only six escaping as by a miracle. Of the whites, none were killed, though some were at the holy Mass. The worst of all is the death of those unfortunates. The mishap has left us without a church, for on account of clefts and breaks it is altogether unserviceable; and because the walls of the fallen part remain high, we dare not work and are in constant fear." Englehardt (1897) states, with reference to San Juan Capistrano: "An apartment in an adjoining adobe has been used ever since for religious service." This indicates that the adobe building withstood the earthquake with relatively minor damage. Ruiz(1812) indicates that other buildings were "in bad conditionâ" suggesting that damage was not confined to the church.

San Gabriel: A description of the earthquake at San Gabriel is given in the 1812 annual report of that mission by Fray Jose de Miguel and Fray Jose Maria de Zalvidea: "All the sacred vessels and other ornaments are in good condition except for the carved statues of Saint Joseph, Our Father Saint Dominic, our Father Saint Francis, and Holy Christ which served on the main altar for the celebration of the mass. All of them were broken to pieces by the violence of a terrible tremor or earthquake which happened on the 8th of December at sunrise. Said earthquake, or tremor, damaged the church considerably and made many cracks in the bell tower, the finial of which fell off along with the weathervane. It also left a crack in the Sacristy and extensively damaged the living quarters of the ministers and the other offices of the mission, not to the extent that they are in danger of collapse, but it will take some work to repair them as best we can.

San Diego: The earthquake is mentioned in the 1812 annual report of Mission San Diego by Fray Fernando Martin and Fray Jose Sanchez: "Thanks be to God we have almost finished building the Holy Church, for we are planning in this year of 1813 to bless it, notwithstanding (in spite of) the great earthquake of December 8." This suggests that any damage at San Diego did not significantly delay the construction of the church. Ruiz (1812), who commanded the garrison at San Diego, describes the earthquake as very strong and that it " . . . was felt in this jurisdiction, without any damage at all in this garrison or in the neighboring mission nor in San Luis." This indicates there was no damage at San Diego (Mission and Presidio) nor at Mission San Luis Rey.

San Fernando: The 1812 annual report of Mission San Fernando (Munoz and Nuez, 1812) mentions "Thirty beams to support the walls of the Church due to the strong and repeated Earthquakes." The date of the damage is not specified, it could have been 8 or 21 December, or indeed damage might have occurred on both dates. Damage on the 8th is reasonable because San Fernando is only 37 km west of San Gabriel, which suffered MM VII damage on the 8th. San Gabriel reports damage on the 8th but does not report the earthquake of the 21st; this indicates no significant damage, even though the buildings had been strongly cracked on the 8th and were susceptible to additional damage. This suggests that any damage at San Fernando on the 21st, was probably to walls that were already damaged on the 8th. San Buenaventura: The damage at San Buenaventura is described in the 1812 annual report from that Mission by Fray Marcos Antonio Victoria and Fray Jose Senan, as resulting from " . . . three horrible tremors or earthquakes, during which it seemed to us that the Mission was coming down", further description of the damage is not specified, but the proximity to Santa Barbara and the similarity of the earthquake effects reported at Santa Barbara and San Buenaventura suggests that they were both damaged on 21 December. Moreover, Arguello (1812) in describing the damage at Santa Barbara from the 21 December earthquake states " . . . and the same thing happened to some at Santa Inez, Purisima, and San Buenaventura", mentioning only the Missions that were damaged on 21 December and not mentioning Capistrano and San Gabriel that were damaged on 8 December. Nevertheless, it is possible that the damage at San Buenaventura started on 8 December because it is attributed to 3 earthquakes in the annual report cited above, whereas Purisima, Santa Inez, and Santa Barbara relate their principal damage to 2 earthquakes of about equal severity occurring a quarter of an hour apart on 21 December, and do not mention a third destructive earthquake. Moreover, the intensity during the 1933 Long Beach earthquake was not less at Ventura than at Capistrano, San Gabriel, or San Fernando (U.S. Earthquakes, 1933). San Bernardino Valley: In San Bernardino Valley, earthquakes were felt frequently in 1812 (Crafts, 1906) and "the hot springs of the valley increased in temperature . . . and a new hot mud spring appeared near Politano, now called Urbita" which is in the present city of San Bernardino. These effects might apply to either or both the earthquakes of 8 and 21 December 1812. No damage was reported in the San Bernardino Valley.

Comparison to 1933 Long Beach Earthquake: Comparison of the 8 December 1812 earthquake with the 1933 Long Beach earthquake shows a similarity in that intensities were high in the Capistrano-San Gabriel area, and were lower in the San Diego-San Luis Rey-San Bernardino area. In 1933, the intensities in the San Fernando-Ventura area were comparable to those in the Capistrano-San Gabriel area; although this is not proven to be the case on 8 December 1812, because of the lack of distinction from the 21 December 1812 earthquake, the available data permit that San Fernando and Ventura were damaged on 8 December 1812.

It thus appears that a source in the vicinity of the 1933 Long Beach earthquake is appropriate for the 8 December 1812 earthquake; candidate fault zones in this area include the Palos Verdes, Newport-Inglewood, Whittier-Elsinore, and Santa Monica-Raymond Hill. The Capistrano-San Gabriel area had intensity VII MM in 1812 and intensity IV to V MM in 1933, indicating the 1812 earthquake was substantially larger than the 1933 earthquake.

From: Toppozada, T. R., C. R. real, and D. L. Parke, 1981. Preparation of isoseismal maps and summaries of reported effects for pre-1900 California earthquakes. California Division of Mines and Geology Open-File Report 81-11, pp. 134-136.