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

Two decades ago, John McCloskey drew a red line on a map of southeastern Turkey to pinpoint where a large earthquake would probably strike. The only question was when.

The answer came last month, when a magnitude-7.8 shock hit the precise location that McCloskey and his team had identified. It struck at 4.17 a.m. local time on 6 February, when most people were asleep, and killed more than 50,000 residents in Turkey and neighbouring Syria.

McCloskey’s work shows both the promise — and limitations — of the science of earthquake forecasting. Although geologists have long attempted to provide warnings of the location, magnitude and exact time of future quakes, decades of research have shown that it’s probably impossible to predict when a geological fault will start to shake. “When you try to winnow it down to know what’s going to happen next, it tends to be a lesson in humility,” says Susan Hough, a geophysicist in the Earthquake Hazards Program at the United States Geological Survey (USGS). “The real focus in most of the world is not on prediction, but on assessing the hazard and the long-term rates of earthquakes.”

Today, researchers work on forecasting: identifying which fault segments are most dangerous and what size earthquakes they are expected to produce. Armed with that knowledge, policymakers can take steps to reduce death and destruction by, for example, requiring better building practices or urging local residents to prepare. Some regions of Japan, the United States and Turkey have developed early-warning systems that alert residents when an earthquake has started nearby. “In principle, you can get rid of seismic risk,” McCloskey says.

Danger zone

Turkey is a seismically active junction at which several pieces of Earth’s crust meet and grind against each other. In southeast Turkey and northern Syria, the Arabian plate is pushing north against the Anatolian plate, squeezing it to the west. But the shift isn’t one smooth movement. Instead, friction holds the plates in place, sometimes for centuries. When the stress overcomes the friction, the plates on either side of the fault line will shudder past each other, releasing tremendous energy in the form of an earthquake.This has happened time and time again in Turkey — a history that allowed McCloskey and his colleagues to map the stresses along one of its major quake sources, the East Anatolian fault. Like other faults, it is divided into segments that slip at different times. When one segment shifts and shakes, it alters the stress on neighbouring sections of the same fault and other faults nearby. That increases the stress in some places, bringing them closer to failure, but relaxes stress on others — making them safer for the time being.

“They are not just randomly occurring earthquakes,” says Ross Stein, chief executive of Temblor, a company specializing in seismic hazard and risk assessment. “They are in a conversation. And that conversation is carried out through stress transfer.”

In 2002, McCloskey (now a geophysicist at the University of Edinburgh, UK) and his colleagues used this technique to diagnose regions on the East Anatolian fault that were highly stressed. With the help of historical records, the team incorporated the stress changes caused by ten earthquakes since 1822 into a model of ongoing plate movement. The modelling suggested that a region of the fault line south of Kahramanmaraş — the precise location and length of the fault that ruptured on 6 February — was at a heightened risk of giving way at some point in the future¹. The team even knew that it would be devastating, forecasting a quake of magnitude 7.3 or higher. “The correspondence is remarkable,” McCloskey says.

Early warnings

Earthquake forecasting could help in other regions as well. California, for example, which is home to the massive San Andreas fault, has implemented the beginnings of an early-warning system that relies on networks of seismometers to detect the very start of a quake. That can provide seconds or minutes of advance notice to Californians to ‘drop, cover and hold on’ while automatically triggering life-saving measures such as slowing trains to a stop. In 2002, Turkey implemented an early-warning system in Istanbul that will slow trains, open lift doors and shut down critical processes in factories in the case of an earthquake. The country has also implemented building codes, but many scientists were concerned that they weren’t being enforced rigorously enough. Mustafa Erdik, a retired civil engineer at Boğaziçi University in Istanbul and president of the Turkish Earthquake Foundation, agrees that this was the case — arguing that ignorance, incompetence and implicit collusion between architects, inspectors and builders were at fault.

That makes February’s aftermath particularly painful for those researchers who have been sounding the alarm for years. “You put a red line on a map, and you understand that means lots of people are going to be killed and their houses destroyed,” McCloskey says.

“The Turkey earthquake to me is, of course, a complete tragedy,” he says. Yet McCloskey is hopeful that we will learn from it. If we do, the next red line he draws on a map will not necessarily equal a catastrophic loss of lives.