What the Turkey earthquake tells us about the science of seismic forecasting

The 7.8-magnitude earthquake that struck Turkey last month destroyed many buildings, such as this one in the city of Kahramanmaraş. Credit: Adem Altan/AFP via Getty

Two decades ago, John McCluskey drew a red line on a map of southeastern Turkey to determine where a large earthquake was likely to strike. The only question was when.

The answer came last month, when a 7.8-magnitude shock hit the exact location McCluskey and his team had identified. The attack took place at 4.17am local time on February 6, when most people were asleep, and killed more than 50,000 residents in neighboring Turkey and Syria.

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McCloskey’s work shows both the promise—and the limitations—of seismology. Although geologists have long tried to provide warnings about the exact location, magnitude and time of future earthquakes, decades of research have shown that it is probably impossible to predict when a geological fault will begin to vibrate. “When you try to hum it to see what happens next, it tends to be a lesson in humility,” says Susan Hough, a geophysicist in the USGS’s Earthquake Hazards Program. “The real focus in most parts of the world is not on forecasting, but on assessing long-term risks and rates of earthquakes.”

Today, researchers are working on forecasting: identifying the most dangerous fault segments and the magnitude of earthquakes expected to occur. Armed with this knowledge, policymakers can take steps to reduce death and destruction by, for example, ordering better building practices or getting local residents to prepare. Some regions of Japan, the United States and Turkey have developed early warning systems that alert residents when an earthquake starts nearby. “In principle, you can eliminate earthquake risk,” says McCloskey.

Danger area

Turkey is a seismically active crossroads where several parts of the earth’s crust meet and grind against each other. In southeastern Turkey and northern Syria, the Arabian plate pushes north against the Anatolian plate, pressing it to the west. But the transition is not one smooth motion. Instead, friction holds the plates in place, sometimes for centuries. When pressure overcomes friction, the plates on either side of the fault line will quiver against each other, releasing massive energy in the form of an earthquake.

This has happened again and again in Turkey—a date that allowed McCloskey and his colleagues to map the stresses along one of the main earthquake sources, the East Anatolian Fault. Like the other defects, it is divided into segments that slide off at different times. When one part shifts and vibrates, it changes pressure on adjacent sections of the same fault and other nearby faults. It builds tension in some places, bringing them closer to failure, but relieves the stress on others – making them safer in the moment.

A fracture cuts a road in Turkey’s Kahramanmaraş region after two strong earthquakes on February 6. Photo: Utku Ucrak/Anadolu Agency via Getty

“It’s not just earthquakes that happen randomly,” says Ross Stein, CEO of Temblor, which specializes in assessing seismic hazards and hazards. “They are in conversation. And that conversation is made through the transfer of tension.”

In 2002, McCloskey (now a geophysicist at the University of Edinburgh, UK) and colleagues used this technique to diagnose areas on the East Anatolian Rift that were under stress. With the help of historical records, the team integrated stress changes caused by ten earthquakes since 1822 into a model of continuous plate motion. Modeling indicated that an area of ​​the fault line south of Kahramanmaraş—the exact location and length of the fault that ruptured on February 6—was at increased risk of retreating at some point in the future. Even the team knew it would be devastating, predicting a magnitude 7.3 or higher earthquake. “The correspondence is great,” says McCluskey.

This isn’t the first time this method, technically known as Coulomb stress transfer, has pinpointed precisely where a twitch is coming. In 1997, Stein and his colleagues analyzed earthquakes that had already struck the North Anatolian Fault in Turkey to estimate that the next earthquakes might occur near the city of Izmit 2. Two years later, this one arrived—killing more than 17,000 people. In 2005, McCluskey and colleagues calculated that a shift in stress after the 2004 Sumatra-Andaman earthquake in Indonesia might cause the West Sumatra 3 Sunda earthquake. This came 12 days after the study was published. And in 2008, Shinji Toda of the Japan Geological Survey in Tsukuba and colleagues predicted that the Wenchuan earthquake earlier that year in China would further stress three adjacent faults. In the next decade, two of those faults caused powerful earthquakes.

added stress

This technology cannot be used everywhere. Because this model requires some knowledge of past earthquakes, often centuries in the past, researchers can use it to assess only areas where the seismic history is well known. They are therefore most successful in predicting aftershocks, which are usually smaller than the main shocks. Still, there are many unknowns, and scientists are working hard to evaluate the model further.

In 2002 Tom Parsons, a geophysicist with the US Geological Survey, analyzed more than 2,000 earthquakes of magnitude greater than 5.5 that occurred after – and soon after – earthquakes larger than magnitude 7. He found that 61% of subsequent earthquakes were associated with an increase in stress caused by their predecessors5. The results indicate that Coulomb stress transfer can accurately identify faults most likely to cause damaging earthquakes, he says. Then, in 2008, Parsons and colleagues published a prediction in the aftermath of the Wenchuan earthquake with the aim of subsequently evaluating model performance6. This work is ongoing.

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Today, Stein, one of the researchers who developed the theory about how forces shift after earthquakes7, estimates that this method has been used in 30,000 papers to explain two-thirds of recent aftershocks and major progressive shocks to our planet. “That tells us this isn’t the only game in town,” Stein says. “Flaws are traits that are bold, messy, and don’t behave the way we’d like.”

McCloskey’s model, for example, predicted the location of the recent Turkey earthquake, but the shaking started on a much smaller branch of the fault and then spread to the main part, a pattern Stein found puzzling. Another complication is that the main earthquake was much larger than expected, perhaps because it re-torn part to the south that erupted in 1822 and part to the north, which erupted in 1893.

“This really underscores the problem with earthquake prediction,” says McCloskey. “Even when we identify the most dangerous place, each earthquake is unique.”

Not long ago, seismologists believed they might be able to predict some earthquakes days or hours before they occurred. Such hopes emerged from Parkfield, California, where earthquakes rock a small section of the San Andreas fault about every 22 years. Both of these earthquakes followed a smaller shock to the north. And hours before a powerful earthquake struck near Parkfield in 1966, the initial movement smashed an irrigation pipeline that bypassed the fault.

“In 1966, earthquake prediction seemed to be our thing,” Stein says. Before the next expected earthquake, geologists wired the area to hundreds of seismometers – hoping to find some precursors that could be used to predict future earthquakes. But when the next earthquake occurred, the researchers saw no warning signs.

Other precursors similarly disappeared. Over the years, scientists have analyzed increasing amounts of radon in local waters, electromagnetic signals from the Earth’s crust and even strange animal behavior. But none of these potential precursors stood up to statistical testing. “Despite all sorts of amazing and promising evidence, we haven’t made an iota of progress toward actually predicting earthquakes,” Stein says.

McCloskey doesn’t think this will ever happen. Most geologists in the West haven’t even worked on that — at least, not anymore, says Hough, who wrote Predicting the Unpredictable (2009). “We know how likely it is that something suddenly appears that we can see before every major earthquake,” says Stein.

Although geoscientists cannot predict earthquakes with any accuracy, many researchers say it is possible to prevent much death and destruction from these natural disasters.

After the 1999 earthquake in Izmit, Aykut Barca, a geologist at Istanbul Technical University, warned that increased pressure could lead to a similar rupture near Duzce, a town about 100 kilometers east. His work convinced the authorities to close school buildings damaged by the İzmit trauma. When a 7.1-magnitude earthquake struck the city two months later, the buildings collapsed.

Early warnings

It can help predicting earthquakes in other areas, too. California, for example, home to the massive San Andreas fault, implemented the beginnings of an early warning system that relies on networks of seismometers to detect the onset of an earthquake. This could provide seconds or minutes of advance notice for Californians to “drop, cover and wait” while automatically triggering life-saving measures such as slowing trains to a stop.

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In 2002, Turkey implemented an early warning system in Istanbul that would slow trains, unlock lift doors, and shut down vital operations in factories in the event of an earthquake. The state also implemented building codes, but many scholars were concerned that they were not being enforced strictly enough. Mustafa Erdık, a retired civil engineer at Bogazici University in Istanbul and head of the Turkish Earthquake Foundation, agrees that this is the case – arguing that ignorance, incompetence and tacit collusion among the architects, inspectors and builders were at fault.

This makes the February consequences particularly painful for those researchers who have sounded the alarm for years. “You put a red line on the map, and you know that means a lot of people are going to be killed and their homes destroyed,” says McCloskey.

“The earthquake in Turkey is, of course, a complete tragedy for me,” he says. Still, McCluskey hopes we can learn from him. If we do, the next red line he draws on the map will not necessarily equal a catastrophic loss of life.

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