The 1787 New Spain earthquake, also known as the San Sixto earthquake, occurred on 28 March at 11:30 local time (17:30 UTC). It caused a large

tsunami A tsunami ( ; from ja, 津波, lit=harbour wave, ) is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquakes, volcanic eruptions and other underwater explo ...

that affected the coast of the Puebla Intendancy (includes the current state of

Guerrero Guerrero is one of the 32 states that comprise the 32 Federal Entities of Mexico. It is divided in 81 municipalities and its capital city is Chilpancingo and its largest city is Acapulcocopied from article, GuerreroAs of 2020, Guerrero the pop ...

) and the Oaxaca Intendancy (currently

Oaxaca Oaxaca ( , also , , from nci, Huāxyacac ), officially the Free and Sovereign State of Oaxaca ( es, Estado Libre y Soberano de Oaxaca), is one of the 32 states that compose the political divisions of Mexico, Federative Entities of Mexico. It is ...

) in Southwestern

New Spain New Spain, officially the Viceroyalty of New Spain ( es, Virreinato de Nueva España, ), or Kingdom of New Spain, was an integral territorial entity of the Spanish Empire, established by Habsburg Spain during the Spanish colonization of the Am ...

(currently part of

Mexico Mexico (Spanish: México), officially the United Mexican States, is a country in the southern portion of North America. It is bordered to the north by the United States; to the south and west by the Pacific Ocean; to the southeast by Guatema ...

). With an estimated magnitude of 8.6 on the

moment magnitude scale The moment magnitude scale (MMS; denoted explicitly with or Mw, and generally implied with use of a single M for magnitude) is a measure of an earthquake's magnitude ("size" or strength) based on its seismic moment. It was defined in a 1979 pape ...

, it was more powerful than any instrumentally recorded Mexican earthquake.

Tectonic setting

Southwestern Mexico lies above the

convergent boundary A convergent boundary (also known as a destructive boundary) is an area on Earth where two or more Plate tectonics, lithospheric plates collide. One plate eventually slides beneath the other, a process known as subduction. The subduction zone can ...

where the

Cocos Plate The Cocos Plate is a young oceanic tectonic plate beneath the Pacific Ocean off the west coast of Central America, named for Cocos Island, which rides upon it. The Cocos Plate was created approximately 23 million years ago when the Farallon Plate ...

is being

subducted Subduction is a geological process in which the oceanic lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, the ...

below the

North American Plate The North American Plate is a tectonic plate covering most of North America, Cuba, the Bahamas, extreme northeastern Asia, and parts of Iceland and the Azores. With an area of , it is the Earth's second largest tectonic plate, behind the Pacific ...

at a rate of 6.4 cm/yr. The dip of the subducting slab is about 15° as defined by

focal mechanism The focal mechanism of an earthquake describes the deformation in the source region that generates the seismic waves. In the case of a fault-related event it refers to the orientation of the fault plane that slipped and the slip vector and is ...

s and earthquake

hypocenter In seismology, a hypocenter or hypocentre () is the point of origin of an earthquake or a subsurface nuclear explosion. A synonym is the focus of an earthquake. Earthquakes An earthquake's hypocenter is the position where the strain energy s ...

s. Seismicity in this area is characterised by regular

megathrust earthquake Megathrust earthquakes occur at convergent plate boundaries, where one tectonic plate is forced underneath another. The earthquakes are caused by slip along the thrust fault that forms the contact between the two plates. These interplate earthqua ...

s along the plate interface.

Earthquake

The earthquake was reported as lasting between 6 and 7 minutes. It was followed by three strong

aftershock In seismology, an aftershock is a smaller earthquake that follows a larger earthquake, in the same area of the main shock, caused as the displaced crust adjusts to the effects of the main shock. Large earthquakes can have hundreds to thousand ...

s on 29 March, 30 March, and 3 April, all of which were probably of magnitude 7 or more, based on estimates of the reported intensities in the city of

. It was felt over a wide area from

Valladolid Valladolid () is a Municipalities of Spain, municipality in Spain and the primary seat of government and de facto capital of the Autonomous communities of Spain, autonomous community of Castile and León. It is also the capital of the province o ...

Tehuantepec Tehuantepec (, in full, Santo Domingo Tehuantepec) is a city and municipality in the southeast of the Mexican state of Oaxaca. It is part of the Tehuantepec District in the west of the Istmo Region. The area was important in pre Hispanic period ...

along the coast and as far inland as

Tulancingo Tulancingo (officially Tulancingo de Bravo; Otomi language, Otomi: Ngu̱hmu) is the second-largest city in the Mexico, Mexican States of Mexico, state of Hidalgo (state), Hidalgo. It is located in the southeastern part of the state and also forms ...

. The magnitude of this earthquake has been estimated from contemporary reports of seismic intensity. Analysis of other subduction interface earthquakes along this margin suggest that the extent of shaking of VIII or greater on the

Mercalli intensity scale The Modified Mercalli intensity scale (MM, MMI, or MCS), developed from Giuseppe Mercalli's Mercalli intensity scale of 1902, is a seismic intensity scale used for measuring the intensity of shaking produced by an earthquake. It measures the eff ...

matches well with the rupture extent for each event. This suggests that the 1787 rupture extended for about 450 km along the coast, providing an estimate of magnitude 8.6, based on scaling against other similar earthquakes.

Tsunami

The tsunami triggered by the earthquake affected the Mexican Pacific coast for more than 500 km along the shores of Oaxaca, Guerrero and

Chiapas Chiapas (; Tzotzil language, Tzotzil and Tzeltal language, Tzeltal: ''Chyapas'' ), officially the Free and Sovereign State of Chiapas ( es, Estado Libre y Soberano de Chiapas), is one of the states that make up the Political divisions of Mexico, ...

. The maximum wave height has been estimated as 18.5 m, based on records of inundation and current elevations.

Damage

The earthquake caused damage to buildings in

Mexico City Mexico City ( es, link=no, Ciudad de México, ; abbr.: CDMX; Nahuatl: ''Altepetl Mexico'') is the capital and largest city of Mexico, and the most populous city in North America. One of the world's alpha cities, it is located in the Valley o ...

and many buildings in Oaxaca City were destroyed. Three churches in Teuchitlan were destroyed.

Future earthquake hazard

The rupture behaviour of the subduction interface in the area of the 1787 earthquake involves occasional very large earthquakes, such as that in 1787, with smaller (M7) earthquakes rupturing just part of the plate boundary during the intervening period. Similar behaviour has been observed along the Colombia-Ecuador subduction zone, with three M7 earthquakes since the M8.8

1906 Ecuador–Colombia earthquake The 1906 Ecuador–Colombia earthquake occurred at 10:36:10 (UTC+5) on Wednesday January 31, 1906 off the coast of Ecuador, near Esmeraldas. The earthquake had a moment magnitude of 8.8 and triggered a destructive tsunami that caused at least 50 ...

rupturing just part of the same area that slipped in that great earthquake.

Tectonic setting

Earthquake

Tsunami

Damage

Future earthquake hazard

See also

References

Further reading