February’s massive earthquakes in Turkey and Syria were what seismologists call a doublet.
The first time the ground shifted the rupture was 300 kilometers long at a magnitude of 7.8. Just nine hours later the second one occurred and it was half as long but almost as powerful. That timing multiplied the tragedy as many people entered buildings after the first earthquake to try to save people and possessions.
“But then the second earthquake with a similar size occurs and it will damage the already weakened buildings again and make extra casualties,” said Zhe Jia, a seismologist with San Diego’s Scripps Institution of Oceanography.
An analysis of Turkey’s earthquakes by researchers at Scripps Oceanography describes a perfect storm of geological circumstances that made the ruptures long and powerful. Researchers also said it holds lessons for California, whose San Andreas Fault is an awful lot like Turkey’s East Anatolian fault system.
“It’s almost a one to one correspondence to the San Andreas (Fault) in terms of the total length, the total displacement and maturity,” said Scripps Oceanography geophysics professor Yuri Fialko. “Also the long term slip rate — the rate at which the plates are moving away from each other at some distance. There are great similarities between these two fault systems.”
Research conducted by Scripps Oceanography scientists is described in an article in the journal Science.
Turkey sits on what’s called the Anatolian Plate, which is squeezed between the Arabian Plate to the south and the Eurasian Plate to the north. As the Arabian Plate pushes northward it is constantly forcing the Anatolian Plate to move.
Fialko said imagine Turkey’s Anatolian Plate is a watermelon seed.
“If you squeeze one between your fingers it will try to shoot out in one direction. And that’s basically what this Anatolian Plate is doing, is trying to shoot to the west. And that motion is accommodated along these very long faults,” he said.
The first earthquake rupture in Turkey began on a short branch of Turkey’s East Anatolian Fault. The analysis by Scripps Oceanography, showed it was a “cascade of ruptures.” It broke through many fault bends and junctions that can usually stop the slippage.
“When a certain fault section ruptures it will communicate with other faults and generate stress, causing the other faults to rupture one by one and the earthquake will turn into a devastating size,” Jia said.
The first earthquake jumped from a branch fault to the main path of the Anatolian Fault.
“It’s known that earthquakes sometimes jump from one fault to the other. The element that was surprising was that it actually jumped and started propagating in both directions,” Fialko said.
The second earthquake was nearly as powerful as its much bigger partner, partly due to the tremendous speed of its rupture. The February earthquakes ultimately killed up to 60,000 people in Turkey and Syria.
The fault lines in the Turkey earthquakes shifted, or slipped, between 8 and 10 meters. The 1994 Northridge earthquake in Los Angeles only slipped 3 meters.
But the 7.8 magnitude earthquake that happened in Turkey could happen here. Fialko said the Anatolian fault line in Turkey should look very familiar to Californians.
Earthquake experts say the magnitude of the first February earthquake in Turkey was roughly the same as the 1906 earthquake that devastated San Francisco.
