Mexico City: Preview of Coming Events
On the night of September 19, 1985, a jetliner packed with journalists, foreign rescue workers and worried family members banked low across the flanks of Mexico City. The twinkling sprawl of suburbia gradually gave way to a black hole at the heart of the city. Only the twisting flames of unquenched fires and pockets of light powered by emergency generators penetrated the gloom. From window seats on short final it was impossible to see the full extent of damage down below, but every person on that plane knew they were about to land in the haze of an ongoing nightmare.
Even on the ground visibility was so limited the arriving passengers could not appreciate how bad things were that first night. Robb Douglas, a Canadian television news cameraman, went to work straight away using a battery-powered lamp to shoot pictures of rescue teams digging through slabs of broken concrete and twisted steel. All he could capture in the small swath of light projected from his camera were close-cropped images of frenzied workers—their grim, sweat-streaked, exhausted faces. Dust and smoke and death.
Early the next morning the scale of the disaster revealed itself. “When the sun came up you could see—holy shit! It looked like it had been bombed—like the city had been bombed,” Robb would tell me later. “All those buildings had just dissolved.” In little more than three minutes of horrific shaking, 10,000 people had died. Unofficial estimates would later push the death toll to 40,000 or more. Another 50,000 were injured and 250,000 were homeless.
In the city proper 3,124 buildings were severely damaged, 412 had collapsed. If you included the impact on outlying regions, more than 6,000 buildings were either destroyed or so heavily damaged they would have to be demolished. With a population of 18 million, the world’s largest city was reeling from the blow and woefully unprepared for the aftermath.
Those of us who did not see it firsthand, who did not stand like Robb on the brink, who did not smell the blood or hear the screams barely paid attention. If we didn’t know someone who lived there, it was one more disaster, far away and too gruesome to think about. But flash back several months to the summer of 1985 and consider the context.
On June 23, a terrorist’s bomb blew Air India flight 182 from the sky off the Atlantic coast of Ireland killing 329 passengers. On July 19, the Val di Stava dam in northern Italy collapsed, killing 268 people. On August 2, Delta Airlines flight 191 crashed near Dallas, killing 137 people. Ten days later a Japan Air Lines flight from Tokyo to Osaka crashed, killing 520, the deadliest single-aircraft accident in history. A crash on September 6, outside Milwaukee killed 31 more. Disasters had dominated the summer headlines with depressing regularity.
On Thursday, September 19, the morning the earthquake wrecked Mexico City, I was working in New York on a Canadian Broadcasting Corporation television documentary about a handful of Russian soldiers who had defected in Afghanistan and escaped to the United States. By the time the first shockwave (magnitude 8.1 on the Richter scale) hit the Mexican capital at 7:19 a.m. local time, the CBC camera crew and I had already left our Manhattan hotel. The front page of The New York Times carried stories about an American hostage in Lebanon freed after 16 months of captivity and a feature about police corruption in Philadelphia but not a word about Mexico City, of course, because the paper had gone to bed the night before.
Off to a good start on the Soviet defector story, I worked my way through the first full day of Mexico’s tragedy without hearing a word about it. I was focused on “Russia’s Vietnam,” blissfully unaware of the mounting death toll in that smoky, flickering cauldron more than 3,000 kilometres to the south and west. I did not know about heroic efforts underway to tunnel beneath the buckled walls and floors of a hospital to find survivors still alive. I could not see the heartbreaking pictures my friend Robb was shooting at that very moment.
Even had I heard a radio newscast as we rattled over potholes and lurched back into New York just before midnight, the Mexico City story probably would not have fazed me as much as it should have. I had never experienced a disaster like that myself, so I had no effective way to process the information, no visceral sense of what it was like to feel the earth heave or to see the known world come crashing down around me. My awareness of distant tragedies was limited to a mental montage of anonymous grieving widows, orphaned children crying, broken men with vacant stares, collapsed buildings and body bags.
Roughly a dozen years in television news and documentaries had sent me around the world more than once, but somehow I’d never been assigned to cover a natural disaster. An evolving cynic at the ripe old age of thirty-six, I had filed plenty of stories about human mayhem from places where the roads were mined and people tended to shoot at each other—places like Nicaragua and Honduras, Sri Lanka and the Punjab. But floods, typhoons and earthquakes were terra incognita.
For me these doomsday stories had an air of unreality about them. The numbing repetition of so much tragedy, packaged neatly in two-minute doses and delivered almost instantly by television news caused in me a blunted reaction. Disaster shock tended to fade quickly.
I was ignorant not just of the people struggling to survive that night in the Mexican capital, but of the scientific significance of the earthquake itself. I would not learn until weeks later that the “event” (as geologists would refer to it) had come as a bit of a surprise. The offshore fault that ruptured had been quiet for perhaps 200 years even though smaller earthquakes had occurred on either side of the epicentre.
The quiescence or absence of quakes on the Michoacán segment roughly 300 kilometres southwest of Mexico City, had convinced some seismologists that this particular fragment of the earth’s crust was for reasons unknown a special case. Two tectonic plates were apparently sliding past each other smoothly. No stress, no worries.
Was there some kind of subterranean lubrication that kept the plates from getting jammed-up? No one knew. But for as long as humans had kept written records, this zone and a few others like it around the world had not generated large, destructive earthquakes. Therefore this particular stretch of the Mexican coast was thought to be aseismic—not likely to produce major earthquakes.
At sunset on Friday, September 20, Robb Douglas and his soundman Gunter Mende, stood at the base of what once might have been a thirty-storey apartment building but was now a twisted heap. Next to the destroyed building stood two more towers that looked like they were part of the same complex. What caught Robb’s eye was the apparent randomness of the wreckage. It was obvious the other two had been badly damaged and could collapse at any moment, but they were still vertical. Why? His pictures raised questions that civil engineers would be forced to answer in the coming months.
As Robb lined up his next shot, the ground started to shake violently beneath his feet. At 6:30 p.m., thirty-six hours after the initial shockwave, a magnitude 7.2 aftershock (some experts believe it was another, completely separate earthquake) instantly made a bad situation worse. People who’d counted themselves lucky, who thought they had survived the disaster, realized in a heartbeat that it wasn’t over yet. Hundreds ran screaming from homes and apartments in the congested neighbourhood surrounding the three towers.
They swarmed across sidewalks and into the streets. Some scrambled into cars and tried to make a getaway, racing toward a nearby freeway onramp. “I got shots of everybody running through the streets, trying to get in their cars to drive away,” said Robb, “but it was hopeless.” A torrent of humanity choked the only avenue of escape.
The TV camera was locked on a tripod and the recording deck was connected by a thick black cable, so Robb and Gunter were shackled together. With nowhere to run, they hunkered down, two rocks in a river of terrified people. “It happened so quickly. It’s not like you have any warning.” The more Robb told me the more vividly the scene came back into focus for him. “We were so frightened, we couldn’t even move. I was just weak in the knees.” This from a guy who doesn’t get rattled by much.
Sensing movement over his shoulder, Robb glanced up and saw in a darkening sky that the two remaining towers, thirty storeys high, were bending side-to-side like tall trees in a wind storm. “When we saw those other two buildings moving back and forth like that, swaying—and you know one had already collapsed—and we were right beside ’em. We figured we were in the wrong place…” But Robb and Gunter were lucky that night. The towers did not fall. And they lived to tell the tale.
Mexico had survived plenty of big earthquakes—forty-two of magnitude 7 or higher in the 20th century—but nothing as big and horrific as the shockwave of September 19 had occurred there in all of recorded history. So geologists immediately started looking for ways to make sense of what had happened. An eerily similar offshore quake had rocked Alaska in 1964. Chile’s 1960 seafloor rupture, at magnitude 9.5, was the largest earthquake ever recorded in the world. In both cases the faults that caused the quakes were impossible to examine, concealed beneath thousands of metres of seawater.
Geologists who’d suggested the Michoacán segment of the Mexican seaboard was somehow a special case—an aseismic zone—were about to face a steep new learning curve. But they weren’t alone. Earth scientists around the world were undergoing a paradigm shift, a fundamental change in thinking about how the planet had formed, how mountains were built and what makes huge earthquakes happen. For more than three decades, starting in the mid-1950s, much of the conventional wisdom of geology had been debated, updated, and revised by fresh data and new ideas.
By the mid-1960s a new hypothesis called plate tectonics had emerged from the dust of an earlier and much ridiculed theory known as continental drift (more on this later). But in 1985, twenty years after tectonic papers began to appear in the science literature, the idea was still relatively new and more than a little controversial. Not everyone had come to terms yet with the concept of slabs of the earth’s crust, 70 to 100 kilometres thick, floating around on convection currents of superheated, semi-liquid rock, crashing and grinding against each other, creating jagged mountain ranges like the crumpled fenders of a car wreck, generating giant earthquakes in the process.
Even basic things like the textbook definition of a fault—a rupture in rock along which movement has taken place—had become vastly more complex in light of new discoveries. It turns out not all faults are simple fractures near the surface on dry land. Unlike the glaringly obvious San Andreas fault in California, where two plates are sliding past each other horizontally (where a geologist can easily stand with one foot on the North American plate and the other on the Pacific plate and straddle the fault to study it), these offshore rupture zones remained a deep, dark mystery. Was the boundary between two plates always vertical? Or could one plate slip underneath another? And if so, at what angle? How could you prove it one way or the other? These were just some of the unknowns that would generate a spirited exchange in the coming years.
In the immediate aftermath of the Mexico City disaster, seismologists, marine geologists and engineers tried to draw conclusions about the underlying cause and what it might mean for other supposedly aseismic zones around the world. Perhaps these monster quakes had happened before but researchers had not looked far enough into the past to find the evidence. Perhaps “all of recorded history” was simply too brief, in geologic terms, to see a repetition of these enormous undersea earthquakes. If it takes several centuries to build up enough stress for a quake this big, perhaps the last one happened so long ago there was nobody around to write it down.
Some scientists thought the Michoacán zone was a “seismic gap” where strong earthquakes (in 1939, in 1973, and again in 1979) had relieved stress on either side of the main segment, but the part in the middle—the Michoacán zone itself—had remained stuck for nearly two centuries. The Michoacán zone was the only part of this tectonic plate that had not snapped free of the continental crust that had drifted over it. It was a holdout—a 145-kilometre slab of sub-sea rock that was bound to fail sooner or later. And when it did, the amount of strain released was unprecedented.
For half a minute that must have felt like a lifetime, 825,000 square kilometres of Central and North America shuddered and rumbled up and down and from side to side. More than 20 million people, some as far away as Los Angeles, Guatemala City, and Corpus Christi, Texas felt the earthquake. Even though the rupture zone was 50 kilometres offshore, south and west of Mexico City, the quake might as well have been directly underneath the downtown core.
Like the lowest notes of an upright bass, this fractured slab of sea floor played fatal music, a throbbing rhythm that pulsed with stunning efficiency through 300 kilometres of continental crust to reach the capital city. The first burst of notes lasted roughly thirty seconds—about the duration of most normal earthquakes that occur closer to the surface. But then another segment of the plate broke loose and the vibrations started again. Many towers that had survived the initial attack were too crippled to endure the second.
As if that weren’t enough, a significant part of the centre of the city was constructed upon a layer cake nine metres thick of sand and gravel and clay, washed into the Mexico Valley from a ring of volcanic mountains. The modern city occupies the same site Tenochtitlan, capital of the Aztec empire, built on the shore of an ancient lake called Texcoco. After Hernán Cortéz conquered the Aztecs in 1521, Spanish engineers drained the lake to make room for a larger settlement. They knew nothing at all about the risk of massive earthquakes from the sea.
Four centuries later eighteen million Mexicans had stacked a sprawling metropolis around and on top of this mudflat basin. When deep bass notes from the Michoacán gap hit the loosely-packed soil, it throbbed and resonated. Apartment blocks on the dried-up lake moaned and swayed to the rhythm of the quake. Swinging side-to-side like inverted pendulums, each tower rang at its own frequency depending on how tall it was. High-rise slabs on the sands of Texcoco were in big trouble.
Every two seconds another shockwave thundered in from the coast like a horizontal pile driver hitting the foundations of the city. Concrete and steel joints were cracking, walls were pulling away from floors. Tall structures standing too close together smashed into each other at the top and tore themselves apart from the roof down. Multi-wing complexes that were not perfectly square or rectangular—those with T-shapes or with a number of sections connected to a central hub—yanked themselves apart at the joints because each wing rattled and snapped to its own beat in syncopated self-destruction.
Anything between six and seventeen storeys tall had a special problem—an internal rhythm in near-perfect synch with the earthquake itself. Shockwaves from the quake caused these mid-sized towers to hum like a tuning fork. This “resonant oscillation” amplified the amount of energy that pulsed through their vertical frames. With the arrival of each new wave, the foundations would be slammed to the side yet again before the rooftops had flexed back to a vertical position. Like rocks along the fault itself, the urban bricks, mortar, and steel inevitably failed.
As stress was relieved along the fault, the continental shelf off the west coast came unstuck from the oceanic plate that had snagged it sixteen kilometres below the surface. The overlying crustal plate snapped free, rebounded sideways as much as 2.5 metres and then sagged. Western beaches slumped as much as 80 centimetres, causing local sea level to rise.
Offshore, while the continental shelf was rattling loose and rebounding to the west, it also heaved upward at the same time. Roughly 7,500 square kilometres of the shallow sea floor lifted a huge mound of salt water. When gravity broke this hump of hoisted seawater into elliptical waves—a train of tsunamis raced across the Pacific.
Given the magnitude of the earthquake, the size of the tsunami was relatively small. From Manzanillo to Acapulco and Zihuatanejo the waves measured from one to three metres but caused relatively little damage. When the tsunami hit Hilo, Hawaii hours later the wave was only 22 centimetres high. One possible explanation was that the ocean floor had been shoved underneath the continental land mass at such a shallow angle that the volume of seawater lifted by the earthquake did not amount to much, compared to other tsunamis generated by large earthquakes.
But in September of 1985, scientists were still struggling to understand what had happened. The intricate details of tectonic motion and the fine points of rock failure far below ground were still pretty sketchy. One thing, however, was clear: a seemingly logical explanation for the lack of major earthquakes off Mexico’s west coast—if we haven’t seen any in all of recorded history, they must not happen here—was wrong.
Since a great earthquake had just happened in a supposedly aseismic zone like Mexico’s, where else might the same thing occur? What about the coast of northern California, Oregon, Washington and British Columbia, also thought to be aseismic? A major disaster like Mexico’s had not happened in the Pacific Northwest in all of recorded history either. By the same logic, if monster quakes were going to happen up there, surely we would have seen one by now.
On the other hand, maybe not. Overnight it seemed anything was possible. Perhaps a megathrust quake could happen on any offshore “subduction zone.” Teams of scientists scrambled to Mexico as quickly as they could to examine this newest twist in the young science of plate tectonics. Ideas about how the world’s largest earthquakes are created would change in the months and years ahead. For some scientists, the Mexico City disaster would be a tipping point.
As I fell asleep that night in New York, I too faced a knowledge gap. I did not know the Mexico City earthquake had become the opening chapter of a story I would soon be covering myself—a plotline I would follow for the next twenty-five years. It’s a mystery that continues to unfold like a dimestore thriller, one that probably will not end for me until my home on British Columbia’s west coast has faced its own megathrust nightmare.