1920 Xalapa earthquake
The 1920 Xalapa earthquake rocked the gulf coast of Mexico on January 4, causing major damage in the states of Veracruz and Puebla. The epicenter was located somewhere in mountainous region of the eastern Trans-Mexican Volcanic Belt which triggered massive mudflows and landslides which claimed anywhere between 700 to 4,000 lives.[1] The event produced extreme ground motions reaching XI to XII on the Mercalli intensity scale. Prior to the 1985 Mexico City earthquake, this was the nation's worst earthquake.[2][3]
  | |
| UTC time | 1920-01-04 04:21:58 |
|---|---|
| ISC event | 912397 |
| USGS-ANSS | n/a |
| Local date | 3 January 1920 |
| Magnitude | 7.8 Ms 6.4 Mw |
| Epicenter | 19.260°N 96.970°W |
| Type | Normal Intraplate |
| Areas affected | |
| Max. intensity | XII (Extreme) |
| Landslides | Yes |
| Aftershocks | Continued until April 1920 |
| Casualties | 648-4,000 dead, 167 injured |
Shaking was felt as far as Toluca in the State of Mexico and throughout the central regions of the country.
Background
Tectonic setting
The west coast of Mexico is dominated by a subduction zone where the Rivera and Cocos Plates converge with the North American Plate at a rate of 3 to 9 cm/yr, varying in locations. At the interface of the subduction zone, earthquakes occur occasionally with magnitudes reaching greater than 8.0.[4] These events are capable of producing tsunamis that devastate coastal communities. At the same time, the subducting plates are still seismically active. Faults within the underthrusted slab which accommodate extension as it flexes and dives into the earth's interior can produce intermediate depth earthquakes that are just as destructive. Intraplate faults in the downgoing slab before subducting can also generate tsunamis.
Trans-Mexican Volcanic Belt
This volcanic range stretches from the country's Pacific Coast to the Gulf of Mexico for more than 1,000 km. It does not run parallel to the Middle America Trench where the plates are subducting due to the difference in subduction angle. Along the southern coast of Mexico, subduction is flat-slab where in the northern area, the plates dive steeply.[5] For that reason, the volcanic arc migrate away from the trench in the south. Earthquakes in the volcanic belt may be a result of active crustal extension within the North American Plate.[6] Seismicity of the volcanic belt is usually low, and rarely do these earthquakes reach magnitudes of 5.0 or greater.
Earthquake
The absence of visible surface ruptures has geologists speculating if this was a blind rupture quake or an intermediate depth event.[7] The source of the earthquake has been the subject of debates and controversy. It had a focal mechanism corresponding to normal faulting with some sense of strike-slip, as seen in other earthquakes in the area. A 25 km fault under the volcanic belt was consistent with the damage and shaking intensity patterns. Ground cracks and fissures thought to be surface ruptures were later correctly identified as slumping rather than faulting.
The Xalapa earthquake may have been an intraplate earthquake occurring at a shallow depth within the North American Plate. Such earthquakes within the overriding plate are infrequent but they have occurred in the past with deadly results. In 1546, a shallow crustal earthquake reportedly caused heavy damage in the affected areas.[8]
Effects
The heaviest damage from the 1920 earthquake was in the vicinity between the volcanic cones of Cofre de Perote and Pico de Orizaba, and around the Sierra Madre Oriental where large landslides triggered by strong ground motions traveled down the Huitzilapa and Pescados river valleys. The flow traveled some 15 km, destroying the towns in the process. The settlements of Acuatlatipa, El Rincón, Mecatitla, and Pet-lacuacán were buried by mudflows, some of them were never rebuilt. Some 300 residents were lost under the flow, and in Barranca Grande, only 80 of the 400 villagers survived. In some places, the mudflow deposits were up to 15 meters thick. It traveled for 80 km before entering the Gulf of Mexico.
The churches in Chilchotla, Santiago Lafragua, and Patlanalán were totally destroyed. Little damage was done to the ground and homes as their building material was mainly wood thus structural failures did not claim any lives. In the village of Ayahualulco however, many of the buildings were constructed with bricks and adobe which was destroyed. The towns of Cosautlán and Teocelo although unaffected by the mudflows lost over 150 inhabitants mostly from collapses. In the city of Xalapa, damage was less severe with churches and buildings sustaining some damage. No collapses were reported.
References
- "Significant Earthquake Information Mexico: Veracruz: Cozautlan, Puebla: Patlanala". NGDC. Retrieved 2 January 2021.
- Torres, G.F.; Castillo, S.; Mora, I.; Leonardo, M.; Hernández, F.; Dávalos, R.; Álvarez, J.L.; Rodríguez, M. (2012). Maps of Seismic Intensity in the Metropolitan Area Xalapa, Veracruz, Mexico (PDF). 15th World Conference on Earthquake Engineering. Lisbon. Retrieved January 2, 2021.
- García, Juan José (3 January 2020). "Sismo de Xalapa de 1920 es el segundo más letal en la historia de México". Formatosie7e. Retrieved 2 January 2021.
- Aubouin, Jean; Stephan, Jean-François; Roump, Jacqueline; Renard, Vincent (1981). "The middle america trench as an example of a subduction zone". Tectonophysics. 86 (1–3): 113–132. doi:10.1016/0040-1951(82)90063-4. ISSN 0040-1951.
- Ferrari, Luca. "The Geochemical Puzzle of the Trans-Mexican Volcanic Belt: Mantle Plume, Continental Rifting, or Mantle Perturbation Induced by Subduction?". Retrieved 2 January 2021.
- Gerardo Suárez, Gema V. Caballero‐Jiménez, David A. Novelo‐Casanova (30 August 2019). "Active Crustal Deformation in the Trans‐Mexican Volcanic Belt as Evidenced by Historical Earthquakes During the Last 450 Years". Tectonics. 38 (10): 3544–3562. doi:10.1029/2019TC005601 – via John Wiley & Sons.CS1 maint: multiple names: authors list (link)
- Suter, Max; Carrillo-Martfnez, Miguel; Quintero-Legorreta, Odranoel (1996). "Macroseismic Study of Shallow Earthquakes in the Central and Eastern Parts of the Trans-Mexican Volcanic Belt, Mexico". Bulletin of the Seismological Society of America. 86 (6): 1952–1963.
- Flores, Teodoro; Camacho, Heriberto; Muñoz Lumbier, M. (1922). "Report on the Mexican earthquake of January 3, 1920". Bulletin of the Geological Institute of Mexico (in Spanish). 38 – via Biblioteca Conjunto de Ciencias de la Tierra.