On Friday, September 8, at 11:11 p.m. local time, in the many villages dotting the High Atlas mountains of Morocco, thousands were turning in for the night, or were already fast asleep. Fifty miles away, hundreds of thousands in the bustling city of Marrakech were doing the same.
Seconds later, a magnitude 6.8 rupture broke out somewhere in the mountains, close to the town of Oukaïmedene. The entire region shook violently—the residual vibrations were felt as far away as the Portuguese city of Lisbon. Countless homes and buildings across an expansive stretch of Morocco crumbled.
The destruction in Marrakech was significant, but much of the city remains standing. That is not the case for many rural villages, some of which have been entirely obliterated. The death toll currently stands at more than 2,600—a number that is expected to rise in the coming days. And now, as potent aftershocks continue to terrorize the region, many are wondering: What exactly happened? Why was this particular earthquake so lethal?
People often focus on a quake’s magnitude, a measure of the size of, and to an extent the energy released during, the rupture in Earth’s surface. This part of North Africa is seismically active, but large earthquakes are not common. And “this earthquake is larger than any ever recorded in the region,” says Judith Hubbard, an earthquake scientist at Cornell University.
The temblor’s high magnitude certainly contributed to the lethality of the disaster. But multiple factors led to the devastation, including the simple fact that this happened at night, when many would be unable to react to the world convulsing around them, and that many of the region’s buildings were not designed to withstand such a powerful quake.
“Unreinforced masonry, like brick and mortar, is notorious for failing during earthquakes,” says Wendy Bohon, an earthquake geologist and science communicator. “This is another devastating reminder that earthquakes themselves don’t kill people, buildings do.”
Scientists are now using knowledge of the region’s geology to work out how the temblor happened, why it proved to be so deadly, and what is yet to be revealed about the forces behind this tragedy. Such research can help the world better prepare for the next major quake, wherever and whenever it may strike.
A bomb beneath the mountains
North Africa sits on the Nubian plate, also called the African plate, which is slowly moving with respect to the Eurasian plate. Morocco is close to, but not on, this tectonic plate boundary. The country is home to an intricate web of varyingly active faults, including many that streak through the High Atlas mountain range.
Small earthquakes are not uncommon in the region, and the gradual movement along this plate boundary means that large earthquakes are relatively rare—but they can, and have, happened. Scientists often cite two especially grave examples: In 1755, the huge Meknes quake (of somewhat uncertain magnitude) killed perhaps 15,000 people; and in 1960, the magnitude 5.8 Agadir quake killed 12,000.
Major earthquakes can strike on all sorts of fault networks—all that is needed is pressure and time. “There’s a lot of tension in the crust” around the High Atlas mountain range, says Thomas Lecocq, a seismologist at the Royal Observatory of Belgium. “And this event looks like it really released that tension.”
Although a large earthquake in the region was inevitable, the location of Friday’s temblor was somewhat surprising.
“Most of the seismicity in Morocco is related to movement on the boundary between the African and Eurasian plate, and therefore the highest level of seismic hazard was thought to exist in the north of the country,” says Jascha Polet, a seismologist and professor emeritus at California State Polytechnic University Pomona. Friday’s quake took place farther south, in a region of low seismicity.
The style of the rupture is thought to be a messy combination of two types: a reverse thrust fault, in which one block of crust jolts up and over another, and a strike-slip fault, where one block moves sideways with respect to the other. “It is mainly reverse with a little bit of strike-slip,” says Paula Figueiredo, an earthquake scientist at North Carolina State University.
The U.S. Geological Survey calculated a depth of 16 miles for Friday’s earthquake. The overwhelming complexity of the region’s fault network, however, and a lack of high-resolution surveys in some areas, means that it is not at all clear which faults were responsible.
“A number of faults and lineaments have been mapped in the range, with no known earthquakes on any of them,” says Hubbard. “There are a variety of older structures in the range, too, due to ancient rifting, that could be reactivated.”
New satellite data examined by Hubbard has revealed where, and how, the ground in the region deformed during the quake. Based on this, she and fellow geologist Kyle Bradley suspect that the fault that most probably ruptured was the Tizi n’Test fault—a fault that few considered to be active. But more data is still needed to confirm this tentative conclusion.
No disaster is natural
In the coming days, a flood of new data will clue scientists into the seismologic cause of Friday’s catastrophe. But what is already known is that many human factors bolstered the quake’s lethality.
Indubitably, a magnitude 6.8 quake—a value that may rise or fall as seismologists refine their calculations over the coming days—is a severe event. But what leads to devastation is the intensity of the quake, a measure of how much the ground shook at various distances from the rupture’s origin.
According to the U.S. Geological Survey, this shallow, powerful quake caused “severe” shaking around the epicenter, and “strong” to “very strong” in Marrakech—high intensities to be sure, but even that alone does not explain why thousands of lives were lost.
“To make a disaster, you need a strong hazard, the earthquake, and strong vulnerabilities, fragile buildings and houses,” says Robin Lacassin, an earthquake scientist at the Paris Institute of Earth Physics.
Although some of the contemporary, concrete buildings in Marrakech largely withstood the earthquake, parts of the old city fared less well. But the damage to this city, while significant, was not nearly as destructive as what occurred in and around the High Atlas mountains.
Structures in these parts, including mudbrick houses and unreinforced masonry buildings, had no chance of withstanding the quake. Emergency responders are still struggling to reach most of the affected settlements, but initial reconnaissance suggests that several have been completely destroyed.
People here tend to live on sediment-laden plains north of the mountains, or on the slopes of the mountains themselves. “Both of these situations can exacerbate damage,” says Hubbard. “The weaker alluvial sediments can amplify shaking, and mountains are vulnerable to landsliding, including along the roads that lead to mountain villages.”
Another lethal feature of Friday’s quake was the timing—both in the immediate sense and on longer timescales.
“The earthquake occurred at night when most would have been asleep inside buildings,” says Polet.
And it also occurred after a long period of calm, with few severe earthquakes in living memory. Although deadly quakes have happened relatively recently—one in 2004, which shook the Mediterranean port city of Al Hoceima, killed several hundred people, for example—the last truly cataclysmic quake in the region was the Agadir earthquake in 1960.
Many people may have been unaware of how to best protect themselves in an earthquake. In areas where building codes ensure structures are quake-resistant, the most broadly useful advice is to drop to the floor, find a sturdy table or similar structure, and hold on until the shaking stops.
For those already outside, the labyrinthine design of parts of Marrakech also contributed to the disaster. “Images also show people fleeing buildings, only to end up in narrow streets between buildings, and therefore still remain at risk from falling masonry,” says Hubbard. “Finding a safe place, away from structures, seems to have been difficult.”
The end of the beginning
The quake was ferocious—but it was over in seconds. The disaster it engendered, though, will last for years.
“We still do not know exactly how deadly the quake was, especially for people living in remote areas,” says Hubbard. As more villages are reached, the death toll will continue to rise.
Survivors, with many having lost family members, friends, homes, and livelihoods, will suffer an incomparable trauma. And the country will be faced with a huge social, economic, and cultural loss—the latest nation rocked by a deleterious earthquake that struck essentially without warning.
One day scientists may crack the seismological code and work out a way to determine that a major temblor is on its way. But for now, all they can do is commiserate and mourn. “My heart breaks for the people of Morocco as they deal with this tragedy,” says Bohon.