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On October 30, when a powerful 7.0 magnitude earthquake struck under the Aegean Sea, dozens of buildings collapsed and water rushed into the streets of the coastal city of Izmir, Turkey, and on the island of Samos, Greece. At least 14 people have died and more than 400 were injured.
This region is no stranger to earthquakes, with a written record of tectonic destruction dating back centuries. But while many earthquake-prone places in the world can trace their seismic activity back to the meeting of just two major tectonic plates, the situation is much more complicated around the Aegean. The source of all the shaking is instead a complicated geological puzzle that forms the area, cut by a network of faults.
“This is definitely one of the most complex regions in the world,” says Joao Duarte, a marine geologist at the Dom Luiz Institute of the University of Lisbon.
The tectonic complexity behind these events makes it even more challenging to understand the hazards in the region, says Laura Gregory, an earthquake researcher at the University of Leeds in the UK.
“There is not one major fault we can focus on, but many faults located in a huge area, most of which could cause a devastating earthquake like the one today,” he tells National Geographic via direct messages on Twitter.
Squeezed like a seed
The many shifting tectonic plates and other seismic forces at play prepare the region for frequent earthquakes. An earthquake with an estimated magnitude of 7 previously occurred near the city of Izmir in 1688. That earthquake changed the landscape so much that the surface dropped more than a foot, and the tremor toppled buildings and ignited fires, killing up to 16,000 people.
In 1903, a magnitude 8.2 earthquake occurred near the Greek island of Kythira, representing one of the largest Mediterranean earthquakes recorded by modern seismic instruments. And between 1993 and 1999, several devastating earthquakes of magnitude greater than 7.0 occurred along the northern part of the Anatolian plate, the main tectonic segment below Turkey.
Geologically speaking, this region is wedged between the zone where the African, Eurasian and Arab plates meet. East of the Aegean, the Arabian plate collides with the Eurasian plate, pushing up a series of mountains that include Zagros, a chain that runs through Iran, Iraq, and Turkey. The colliding plates also send the Anatolian plate westward, as if “it’s being pushed like a watermelon seed between two fingers,” says Robert Stern, a tectonics expert at the University of Texas at Dallas.
The latest earthquake occurred approximately 13 miles below the Aegean seabed, about nine miles off the coast of Samos. This relatively shallow depth meant that strong tremors were felt both on the Greek island and in cities along the Turkish coast. The epicenter is at the western edge of the Anatolian plate, where the rocks on the surface stretch like putty. This stretching produces a series of deep fractures in the ground, and movement along one of these cracks triggered the recent tremor.
Why this region is breaking up in this way “is hotly debated,” says Ezgi Karasozen, a seismologist at the Alaska Earthquake Center whose doctoral research focused on the earthquakes in Iran and Turkey, by email. There is likely a combination of three main forces behind the extension, he notes.
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One source comes from the effect of the watermelon seed, which causes what Karasozen calls “escape tectonics.” As the larger Arab and Eurasian plates move around the Anatolian plate, the crust rock is pushed and squeezed.
Another major source of stretch is known as slab recoil, which occurs when one tectonic plate coils under another and into the mantle, says Robin Lacassin of the Institut de Physique du Globe in Paris in a direct message on Twitter. You can imagine the slab going back by placing your left hand flat on your right and slowly bending the fingers of your right hand; that’s the slab falling back and down into the depths.
This movement pulls on the overlying plate and the resulting stretching is called “slab suction,” says Duarte, because the underlying plate essentially sucks rocks from the surface. This process occurs when the African plate dives under the western half of the Anatolian plate, under the Aegean Sea.
Another likely force at play could be a fairly simple one: gravity. The center of the Anatolian plate is thick, which means “everything wants to sink in and expand around the edges,” says Gregory.
Scientists are now baffled by this latest event, which is unusually large for the region where it occurred, Karasozen says. As teams monitor the aftershocks, which continue to echo, the data promises to help future scientists better understand the dangers woven into the region’s wild tectonics. Just by studying past and current events, scientists can hope to improve their understanding of the risks around the Aegean and potentially one day forecast the earthquakes of the future.
