Mexico City sits on a drained lakebed that amplifies seismic waves and has a public alarm system that buys you up to a minute of warning. Here is how to use it.
When the alarm sounds, drop to the floor, take cover under a sturdy table or desk, and hold on. If no table is nearby, crouch beside a large fixed appliance like a refrigerator, which can create a protective void. Don't stand in a doorway — that advice is outdated. If you're outside, move away from buildings and power lines and stay low. After the shaking stops, leave the building calmly using stairs, not the elevator, and don't re-enter until authorities say it's safe.
Mexico City is one of the most seismically active cities on earth, and it sits on a particularly treacherous piece of ground: the drained lakebed of ancient Lake Texcoco, a layer of soft clay that amplifies seismic waves the way a bowl of gelatin amplifies a tap on the table. When an earthquake originating hundreds of kilometers away on the Pacific coast reaches the valley, the ground here can shake at two to three times the intensity felt at the epicenter. That fact shapes everything about how the city prepares and responds.
Mexico City’s public seismic early warning system, SASMEX, detects earthquakes at their origin point on the coast and broadcasts an alarm to the city before the waves arrive. Depending on where the earthquake starts, that window can be anywhere from a few seconds to about a minute. The alarm is a repeating rising tone broadcast through outdoor speakers mounted throughout the city. You will hear it. When you do, you have time to act before the shaking starts.
The alarm does not always fire. Earthquakes that originate very close to the city, or directly beneath it, arrive faster than the system can warn. The 2017 earthquake had no useful warning time at that proximity. Know what to do before the alarm goes off, because sometimes it doesn’t.
Drop, cover, and hold on. Get down on hands and knees. If a sturdy table or desk is nearby, get under it and hold on to a leg. Protect your head and neck with your arms. Stay away from windows, exterior walls, heavy furniture that can fall, and anything hanging from the ceiling.
The doorway advice is wrong. For decades, the received wisdom in Mexico — and elsewhere — was to stand in a doorway during an earthquake, a holdover from a time when doorframes in adobe buildings were the strongest structural element. In modern reinforced concrete construction, doorways offer no special protection and are often in the middle of the most active areas of a building. Mexican civil protection authorities updated this guidance after the 2017 earthquake.
If no table is nearby, get beside the refrigerator. The current guidance from Mexico’s Secretaría de Gestión Integral de Riesgos y Protección Civil recognizes what’s called the “refuge triangle”: large, solid fixed appliances like a refrigerator or a washing machine are heavy and structurally dense enough that if a ceiling or wall collapses, the appliance can bear weight and create a survival void beside it. Crouch beside the appliance, not under it, and protect your head. This is a specific addition to guidance following structural analysis of building collapses in 2017.
If you’re outside, move away from buildings and stay in the open. The main danger outdoors is falling glass, facade pieces, and debris from the upper floors of buildings. Don’t run back inside to retrieve anything.
After the shaking stops, look up before you move. Downed power lines are a serious secondary hazard that doesn’t get enough attention. A line on the ground may still be energized. Assume any downed line is live, give it a wide berth, and alert others. Don’t touch any metal surface near a downed line. If you’re in a car and a line falls on or near it, stay inside until emergency services arrive and tell you it’s clear.
Secondary hazards also include gas leaks. If you smell gas after leaving a building, don’t light anything, don’t operate light switches, and put distance between yourself and the building.
Leave the building using the stairs. Do not use the elevator. Even if a building looks undamaged from the inside, there can be structural damage that isn’t visible. Mexico City’s building stock varies enormously in age and quality; the 1985 earthquake exposed catastrophic failures in construction that met code on paper, and the city has been improving its enforcement since, but older buildings remain.
Check in with your group or whoever is expecting you. Cell networks often saturate immediately after a major earthquake as everyone calls at once; texts go through more reliably. WhatsApp and other data-based messaging apps typically work before voice calls do.
Aftershocks follow major earthquakes. The 2017 quake had dozens of significant aftershocks in the days and weeks after. If you feel another tremor while you’re inside a building after a quake, treat it the same way: drop, cover, hold on, and get out when it passes.
The September 19, 1985 earthquake, an 8.1-magnitude rupture off the Pacific coast, killed at least 10,000 people in Mexico City — the official count was lower, but independent estimates ranged much higher — and collapsed hundreds of buildings across the city center. The response by the Mexican government was widely seen as too slow and too disorganized, and out of that failure came something remarkable: ordinary residents organized their own rescue operations before official help arrived.
The group that formed in Tlatelolco during those first chaotic days became the Brigada de Rescate Topos, known simply as Los Topos — the moles. Volunteer urban search-and-rescue specialists trained in finding and extracting survivors from collapsed structures. In the years since 1985, Los Topos and their trained search-and-rescue dogs have deployed to earthquakes, floods, and structural collapses across the world: El Salvador, Haiti, Ecuador, Nepal, Turkey, and dozens of others. The image of the Topos arriving in a disaster zone with their dogs has become one of Mexico’s most recognized expressions of civic solidarity. The dogs are trained in scent detection and can locate survivors in debris that would take human teams days to search by hand.
The 1985 earthquake also produced SASMEX, the seismic alarm network, and a comprehensive overhaul of the city’s building codes. An earthquake of similar magnitude today would still cause damage, but the city that rebuilt after 1985 had fundamentally different infrastructure and a population that knew what to do.
September 19 became a date the city does not forget. Mexico observes a national earthquake drill every year on that date. On September 19, 2017, the annual drill had been completed that morning when a separate 7.1-magnitude earthquake struck at 1:14 p.m., killing roughly 370 people in the metropolitan area and collapsing dozens of buildings. The coincidence of dates — 32 years apart to the day — was not lost on anyone.
Identify the exit routes from wherever you’re staying. Note where the stairs are relative to your room or apartment. Know the nearest open space (a park, a wide street, a plaza) in your immediate neighborhood; that’s where to go once you’re out of the building. If you’re in a hotel, ask whether they have a seismic protocol and what it is. Most good hotels have floor wardens and a designated assembly point.
The alarm can give you up to a minute. Know in advance what you’ll do with it.
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