Alerta sísmica! Alerta sísmica!” Few things strike as much fear into the hearts of Mexico City residents as the words “seismic alert” blaring from speakers in schools and parks. It means an earthquake is rumbling up from the Pacific coast, and you have 60 to 90 seconds to get someplace safe.
I had just turned out the light to go to sleep when the alarm went off last night at almost midnight. My husband and I heard it from the elementary school next to our apartment building. We both grew up with earthquakes—him in Mexico City, me in Los Angeles—but we still spent the first 10 seconds in disbelief. A false earthquake alarm had gone off the day before, due to human error during maintenance of the system. The few other times I had heard the alarm, the resulting shaking had barely registered in my building. Couldn’t we ignore it and go to sleep?
¡Alerta sísmica! ¡Alerta sísmica! “Pocas provocan tanto miedo en los corazones de la CDMX como las palabras ” alerta sísmica” resonando en altavoces, en escuelas y parques. Eso quiere decir que un terremoto retumba encima de la costa del Pacífico, y usted tiene 60 a 90 segundos para ponerse a salvo.
Ciudad de México es uno de los pocos lugares que tiene suerte de tener un sistema público de alerta de terremoto. Fue el primer sistema de este tipo en el mundo y sólo seis años después del terremoto de 1985 que mató a decenas de miles de personas en la capital. Ciudad de México tiene una ventaja geológica incorporada cuando se trata de sistemas de alerta temprana: la zonas de subducción que producen los terremotos están a lo largo de la costa del Pacífico, a más de 200 millas de la ciudad.
La alerta sísmica no nos dice nada sobre la intensidad, así que no había ninguna manera de saber qué tan fuerte sería el temblor. Resultó ser el terremoto más grande registrado en México en un siglo, magnitud 8,2 en el epicentro de 54 millas de la costa de Chiapas.
No. Mexico City is one of the few lucky places to have a public earthquake warning system at all. It was the first system of its kind in the world, up and running just six years after the 1985 earthquake that killed tens of thousands of people in the capital. Mexico City has a built-in geological advantage when it comes to early warning: The subduction zones that produce the quakes are along the Pacific coast, more than 200 miles away from the city. While seismic waves normally would peter out over that distance, here they are amplified by the pile of mud upon which Mexico City is built, the remnants of a large lake drained during the colonial period. That can make for some particularly deadly earthquakes. But it also gives us time to learn that one is on the way.
I scooped up my dog and ran to get under the dining room table, my husband right behind me. Many people in Mexico City run out of their buildings when they hear the seismic alarm, an instinct honed by the memories of pancaking hospitals and tumbling apartment towers in 1985. We’re on the third floor, though, and I didn’t think we could get to the courtyard within the 1-minute warning window—especially not with a cat and a dog. Plus, everything about my California earthquake training told me to get underneath something and stay put; my building might fall, but so might trees and power lines outside. From our spot under the table, we could hear some of our neighbors in the hallway. They were laughing sheepishly, seemingly a bit embarrassed to be so frightened by an alarm and unsure whether evacuating was really necessary. We were under the table long enough for me, too, to wonder if it might be another false alarm. But then the ground started rolling beneath us. That’s when our neighbors started running.
The seismic alarm doesn’t tell you anything about intensity, so there was no way to know how strong the quake would get. It turned out to be the largest earthquake recorded in Mexico in a century, clocking in at 8.1 magnitude at the epicenter 54 miles off the Chiapas coast. In Mexico City it lasted a full minute, the floor heaving, the building creaking, furniture rattling. I focused on every breath, just trying to get to the next one. But nothing fell in our apartment—much less the building itself—and our electricity stayed on. As soon as I was sure it was over and my dizziness passed (earthquakes in Mexico City can feel like being on a boat because of our Jello-like ground), I opened Twitter to see how the rest of the city had fared.
My feed had erupted with videos of everything from lampposts to the giant Angel of Independence monument swaying feverishly. People filmed transformers exploding, sending sparks flying and leaving many neighborhoods without power. The city’s emergency services jumped into action, pushing out data about the quake and fanning out to check for damage while warning of aftershocks.
It was quickly apparent there had been only minimal damage in Mexico City. A few factors spared us from a repeat of 1985. The epicenter was farther from the city this time, and it occurred deeper in the crust. Building codes have been updated and stringently enforced since 1985, when many shoddy structures—some authorized through corrupt government contracts—collapsed into rubble. Since there was no widespread destruction, the early-warning alarm likely didn’t save any lives this time, but it worked just as it was meant to. Mexico City residents are relieved. Sure, we got lucky geologically, but we also benefited from measures implemented to protect the capital, which withstood their strongest test yet.
Large swaths of these states are rural and isolated, and it will likely take several days to understand the true extent of the devastation. The sensors for the early-warning system run up and down the Pacific coast, and some of the cities there, such as Acapulco, have an early-warning system (though residents there necessarily have a shorter window to get to safety, because they are closer to where the quakes originate). These coastal areas help protect us from earthquake damage in Mexico City, but due to poverty and isolation they are some of the least protected.
Mexico is a very centralized country, with political, cultural, and economic life revolving around Mexico City. The trauma of the devastated capital in 1985 is seared into the country’s psyche, and for good reason. People who remember it say it looked like the city had been bombed; you could smell the dead bodies for days. But in its wake, the city and country stepped up to do everything they could to prevent another disaster of that scale here. So far, it’s worked. But the devastation in the south makes it clear that communities that are even more at risk haven’t received the same protection. They don’t have building codes nor the inspectors to enforce them. They don’t have early-warning alarms. Many don’t even have reliable roads by which help can arrive. For too long, Mexico City has been the only place on people’s minds when it comes to earthquake preparedness and protection. Perhaps this is the quake that will finally change that.