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In the smalL hours of February 6th an enormous earthquake ripped across southern Turkey and northern Syria. It flattened thousands of buildings, trapping their inhabitants in the rubble. Several aftershocks—one almost as violent as the initial quake—followed a few hours later. At the time of publication, more than 3,400 people had been reported dead, with many more injured. The numbers seem certain to rise. Recep Tayyip Erdogan, Turkey’s president, said the country had been shaken by the “strongest disaster in a century”. But why was the earthquake so deadly, and what could have been done to protect people from it?

Earthquakes are caused by the movements of tectonic plates, great segments of Earth’s crust that are dragged about by convection currents in the hot mantle below. Plates vary in size. The Juan de Fuca plate off America’s north-west coast is about as big as the nearby state of Oregon, and the Pacific plate occupies nearly a fifth of the world’s surface. Plates move slowly and sometimes stick and jam against one another in geological faults, creating a buildup of tension. When that grows too great, they can slip suddenly past each other, causing the type of earthquake experienced in Turkey and Syria.

Turkey is an earthquake hotspot. Much of it sits on the Anatolian plate, a small block of crust squeezed between four other plates, including the Arabian plate to the south-east, which is pushing north-west, and the much larger Eurasian plate to the north, which is moving south-east (see map). Earthquakes are common, though most happen along the North Anatolian fault, the boundary with the Eurasian plate, which runs close to Istanbul. The most recent quake occurred along a different fault, the East Anatolian, which marches with the Arabian plate.

Several things have conspired to make this quake especially damaging. One was its strength. Its magnitude was estimated at 7.8, and the most powerful aftershock registered 7.5. On average there are around 15 earthquakes stronger than magnitude 7 a year. (Because the scale is logarithmic, every one-point increase in magnitude means a 32-fold increase in the amount of energy released.) Its relatively shallow origin (initial analysis suggests its focus was just 18km, or 11 miles, deep) would have magnified the amount of force felt at the surface.

Factors above the ground have made things worse. The initial quake happened at night, when people were asleep indoors, leaving them little chance to escape. Winter cold will threaten the survival of those trapped under the rubble. In Syria, devastated by years of war, the authorities may struggle to organise an effective response.

Although meteorologists can predict disasters like hurricanes or floods, seismologists cannot yet do the same with earthquakes (though it is an active area of research). The most they can offer are devices which detect the fast-travelling pressure waves from a quake that arrive a little before the ground-convulsing shear waves turn up. But these give warnings of only a minute or so at most, and are expensive to maintain.

For now, the best that can be done is to prepare for the worst. Earthquake-prone countries, Turkey among them, generally require buildings to be constructed to resist the forces quakes unleash. But many edifices predate such rules, and corruption means the rules are often ignored by builders. Preparation is further hindered because, even in hotspots, truly devastating earthquakes are rare. The East Anatolian fault has not recorded a quake of this size since the advent of modern monitoring systems, more than a century ago. ■

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