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Mexico is a seismically active part of the world and is impacted by the movements of several tectonic plates. Earthquakes are a recurring phenomenon here due to Mexico´s its geographic location, and throughout history, earthquakes have caused both loss of life and severe damage in the country. Today, the nation is investing a lot in early detection systems and public education, while also enacting and enforcing stricter building codes.
Why is Mexico earthquake-prone?
The primary cause of earthquakes in Mexico is the movement of the Cocos, Pacific, and North American tectonic plates. The Cocos plate, in particular, constantly moves under the North American plate, resulting in frequent seismic activity along Mexico’s Pacific coast. This phenomenon, known as subduction, is the primary cause of the country’s frequent and often devastating earthquakes.
Examples of notable earthquakes in Mexico
June 3, 18 and 22, 1932
On June 3, 1932, an 8.1 Mw earthquake struck Mexico. It was to be the first in a series of three serious earthquakes that would shake Mexico throughout the month of June that year, all reaching a magnitude of at least 7. They became collectively known as the Jalisco Earthquakes of 1932.
The June 3 earthquake had its epicentre off the coast of Colima and Jalisco, and caused widespread damages along western Mexico. The Guadalajara area was especially affected, and there were 300 deaths reported from that area alone. In total, at least 400 deaths were reported from Mexico and Guatemala. The quake registered at 8.1 and had a perceived intensity of X (Extreme) on the Mercalli scale.
On June 18, a 7.7 earthquake struck with an estimated rupture length of 60 km. It lasted for 22 seconds and a majority of the deaths from this one were reported from around the city of Colima. Much fewer people died form this earthquake than from the previous one, perhaps because a lot of people were still sleeping outdoors, as they had been scared by the June 3 quake.
The final of the Jalisco earthquakes occurred on June 22. It was less powerful, “only” reaching a magnitude of 7, but within a few minutes a tsunami generated by the quake reached the coast and the wave caused widespread destruction, including circa 100 deaths and an almost complete devastation of the homes and hotels in Cuyutlán. The city of Colima, where residents were already struggling since the June 18 quake, took in circa 2,000 refugess from the coast.
September 19, 1985
One of the most devastating earthquake event in Mexico’s history occurred on September 19, 1985. This was actually an event with two epicenters and the second shake started 26 seconds after the first. In total, ground shaking lasted for over 5 minutes along certain parts of the coast, while the shaking in Mexico City was somewhat shorter in duration. The September 19 event was then was followed by a 7.5 after-shock on September 20.
With a maximum magnitude of 8.1, the September 19 event had its epicenters off the Pacific coast of Michoacán. Shockwaves hit the mouth of Río Balsas at 7:12 am and reached Mexico City two minutes later. The event reached a Mercalli intesity of IX (Violent).
The epicentre for this event was located off the coast, along the Middle America Trench, but Mexico City – more than 350 km away – was still heavily damaged. The disaster resulted in the loss of at least 5,000 lives and caused extensive damage om the Greater Mexico City area.
Even though the states Jalisco, Colima, Guerrero, and Michoacán were closer to the epicentre, they suffered less damage than Mexico City, with one notable exception – roughly 60% of the buildings in Ciudad Guzmán were destroyed and 50 people killed. The coast and most of the western inland was protected by the fact that it sits on bedrock, which transmitted the shockwaves but did not amplify them. Mexico City is built on an ancient lakebed and, therefore, much more vulnerable, and Mexico City also had more tall buildings.
In Mexico City, the buildings most damaged were 6-15 stories in height. Both lower and taller buildings in the city fared better, generally speaking. Also, buildings erected after the 1957 earthquake, but before the new stricter regulations resulting from the 1976 earthquake were in place, were more likely to have sustained serious damage. This was an era when Mexico City started to build upwards, typically in the 6-15 floor range, but without the benefit of the post-1976 building code.
One famous example of a building that survived almost undamaged was the 44 stories tall Torre Latinoamericana, built in 1948-1956. This building had been built with 200 piles extending down 30 metres into the stable earth stratum, even though that was not mandatory at the time. It handled both the 1957 and the 1985 earthquake remarkably well.
September 7 and September 19, 2017
More recently, in September 2017, two severe earthquakes struck Mexico. The first, on September 7, registered a 8.2 magnitude near Chiapas, and was followed by a 7.1 magnitude earthquake on September 19 that caused great damage in Mexico City and surrounding states.
The Chiapas earthquake of September 7 struck at 04:49 local time when most people were a sleep. The epicentre was in the Gulf of Tehuantepec off Mexico´s southern coast, near the state of Chiapas. The moment magnitude was Mw 8.2 and it had a Mercalli intensity of IX (Violent). Even though the epicentre was off the southern coast, the quake was powerful enough to cause Mexico City to tremble. This was the second-strongest earthquake recorded throughout the history of the country; only the infamous 1787 earthquake is considered stronger. It was also the strongest earthquake recorded anywhere in the world during the year of 2017.
With Mexico still being on edge from the September 7 earthquake and its after-shocks, a new earthquake struck later that same month, on 13:14 CDT (local time) on the 19th of September. This earthquake had its epicentre roughly 55 km south of the city Puebla in southern Mexico and produced strong shakings for about 20 seconds. It had a magnitude of 7.1 Mw and caused damage in the states Puebla and Morelos, as well as in the Greater Mexico City area. 370 people were killed, either directly or by related building collapses. Over 6,000 people were injured.
The September 19 earthquake coincided with the commemoration of the 1985 Mexico City earthquake, which occurred on that date 32 years earlier. Because of this, a national earthquake drill had been carried out in Mexico that day, starting at 11 am local time, roughly two hours before the earthquake struck.
Earthquake Preparedness in Mexico
Mexico has made substantial strides in mitigating the impact of earthquakes. The country boasts one of the world’s earliest warning systems, the Seismic Alert System (SAS), allowing residents up to a minute’s warning before an earthquake hits. This system, coupled with better building codes and regular earthquake drills, has significantly improved the nation’s preparedness for seismic events.
With advancements in technology, Mexico continues to invest in seismic research to improve early detection systems. Scientists are now able to monitor plate activity more closely, providing a better picture of where and when earthquakes might occur.
Yet, while these advancements are promising, predicting earthquakes with absolute certainty remains an elusive goal. Hence, strict building codes, public education, and general disaster preparedness present at all levels of the public and private sectors continues to be the most reliable defense against the effects of earthquakes.