Washington: A massive, deadly earthquake struck southern Turkey before dawn local time on Monday. The 7.8-magnitude quake has killed thousands of people in Turkey and neighboring Syria. It also triggered dozens of destructive aftershocks.
Why do earthquakes happen in this region, and how unusual is the latest event? Here’s what we know so far.
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What do we know about Monday’s earthquake?
The earthquake struck at 4:17am local time near the town of Nurdagi in Turkey’s Gaziantep province, causing destruction and death in Turkey and neighbouring Syria. People felt shaking as far away as Cyprus and Lebanon.
Earthquakes are measured by their magnitude, which is set up as a logarithmic scale. That means that each whole number represents a tenfold increase in strength. While there’s technically no upper limit, the most powerful quake on record is a magnitude 9.5 that struck Chile in May 1960. Based on this scale, a 7.8-magnitude quake is very powerful.
Dozens of destructive aftershocks, smaller earthquakes that occur in the same general area after the main temblor, have continued to shake the region. A 6.7-magnitude aftershock occurred 11 minutes later. And a 7.5-magnitude earthquake that struck after 1pm local time may have been a “doublet” earthquake, one of similar magnitude that occurs close to the original spot.
What causes earthquakes in Turkey?
Turkey sits in an earthquake hot spot. Three tectonic plates - the Arabian, Anatolian and African plates - meet in this region, and as they slide past and squeeze against each other, they build up friction and stress that gets released as earthquakes, according to Yaareb Altaweel, a seismologist at the National Earthquake Information Centre in Colorado.
The Arabian plate is plowing northward at a rate of about 11 millimeters (just under a half-inch) per year, said Stephen Hicks, a seismologist at University College London. Turkey, which sits on the Anatolian plate, is therefore being squeezed westward.
That movement means Turkey has two major faults where earthquakes originate: the 930-mile-long North Anatolian fault and the more than 300-mile-long East Anatolian fault. Many of Turkey’s largest quakes originate on the northern fault, and it has gained the most attention because of the potential for a major quake near the population center of Istanbul.
But this one is thought to have struck along the East Anatolia fault zone - which has been flying a bit under the radar, with no earthquakes greater than magnitude 7 “at least since our seismological monitoring network has been in place - the 1900s,” Hicks said. The lack of recent large earthquakes in the last century along that fault, combined with the northward movement of the Arabian plate, suggest there was pent-up strain in the region, he said.
In this case, the quake happened at what’s known as a strike-slip fault, a fracture in the Earth’s crust where the rocks slide past each other horizontally when they break.
Why was this quake so deadly?
The grim death toll is a result of several factors: the sheer size of the quake; the fact that it struck relatively close to the surface; and its proximity to where people live. Monday’s quake originated just about 11 miles below the surface. That means the seismic waves did not have to travel far before they reached buildings and people on the surface, leading to more intense shaking.
The aftershocks from this quake have also been large - and are expected to continue, Altaweel said.
“So far, we’ve got more than 50 aftershocks,” Altaweel said. “What caught the attention of the media is the big ones,” but the aftershocks can also be destructive.
Would better building codes have helped?
The US Geological Survey warned in its report about this event that “the population in this region resides in structures that are extremely vulnerable to earthquake shaking, though some resistant structures exist.”
USGS highlighted buildings that use unreinforced brick masonry and low-rise concrete frames to be at greatest risk. These materials are too stiff to sway with the shaking and are more likely to buckle, leading to catastrophic collapses.
While better building codes can help, the shallow 7.8-magnitude earthquake caused very intense shaking in a region within Turkey that, unlike the north, had not routinely experienced such large temblors.
“In the southeastern part of Turkey, they hadn’t felt a strong earthquake in most people’s lifetimes,” Hicks said.
What are past examples of notable quakes in this region?
Monday’s event is thought to be the largest quake to occur anywhere in Turkey since 1939, when a 7.8-magnitude earthquake struck in the northeastern part of the country. In March 1970, a destructive 7.1-magnitude earthquake hit western Turkey, killing more than 1,000 people and destroying more than 8,000 buildings.
And in August 1999, a devastating 7.4-magnitude earthquake shook northwestern Turkey, causing more than 17,000 deaths and displacing more than 250,000 people. It was followed by another 7.2 earthquake a few months later that killed more than 800 people. A 6.7-magnitude earthquake also struck eastern Turkey on Jan. 24, 2020.