How regional fault lines led to such a destructive earthquake in Turkey, Syria

It was only a matter of time before the region surrounding Turkey and Syria experienced "the big one," according to experts.

Tens of thousands of people died in a pair of cataclysmic earthquakes that rocked the region on Feb. 6. First, a 7.8-magnitude earthquake struck Gaziantep, in southeastern Turkey along the border of Syria, followed by a 7.5-magnitude quake nine hours later about 100 miles north of the first, with hundreds of aftershocks in between and beyond.

The quakes took down thousands of buildings in the two countries, killing at least 42,000 people.

While individual earthquake activity is difficult to predict, it was never out of the realm of possibility that a large earthquake would be on the horizon in the region, experts told ABC News.

Turkey lies at the crossroads of tectonic plate activity

The complex tectonic activity that lies beneath essentially ensured that a devastatingly strong earthquake would eventually rock the region, the scientists said.

There are four tectonic plates, massive slabs of rock made of up Earth's lithosphere, that interact in Turkey. The Arabian and African plates are moving to the north and interacting with the Eurasian plate, which is essentially in place as a boundary to the north, Joshua Russell, a professor of seismology at Syracuse University, told ABC News.

"That stress is essentially squeezing Turkey out to the west into the Aegean," Alexander Stewart, a professor of geology at St. Lawrence University, told ABC News.

Picture a banana being squeezed out from between the peels, and that is essentially how Turkey is being exuded out into the Aegean Sea as a result of the plate interactions, Stewart said.

What makes Turkey even more vulnerable is the movement from the Anatolian plate is essentially slipping along the fault lines of the North Anatolian fault zone, the most seismically active fault zone in the world, Stewart said.

However, it was the East Anatolian fault zone responsible for the most recent deadly quake, which extends down, through Syria. The energy released from the "rock-to-rock slippage" of the plates onto the East Anatolian fault, which is less active than the North Anatolian fault, is more catastrophic than earthquakes that are releasing the stress on a more consistent basis, Stewart said.

Although the earthquake had a significant magnitude, the readings, which measures the amplitude of the wave forms, or how much fault is moving, on the seismograph don't tell the full story of the strength of the earthquake.

The earthquake involved a break on fault extended for 300 kilometers, or more than 186 miles, Susan Hough, a seismologist at the U.S. Geological Survey, told ABC News.

"The bigger the fault, the bigger the earthquake," Russell said, adding that the shallower the earthquake, the more ground motion that occurs.

When the quake happens, it does not shake all at once. From the epicenter, the rupture travels down the fold at about 3 kilometers per second, Hough said. So if it continues for 300 kilometers, it's actually moving for 100 seconds, Hough said.

So in addition to the very long duration of the quake, it's also impacting a "huge" area, Hough said.

Stewart estimated that Turkey is in the top 20% of regions in the world that would experience devastation due to earthquakes.

A 7.3-magnitude earthquake in Fukushima, Japan, in March 2022 only killed four people. The magnitude of the earthquake was not "out of the ordinary," but although Japan is an earthquake-prone region, the country's economic system is able to provide and engineer structures to withstand moderate earthquake magnitudes.

The same can't be said for regions like eastern Turkey and Haiti.

In 1936, the North Anatolian fault ruptured beneath Marmara Sea, which also led to tens of thousands of deaths. It was then that building codes began to be instated in the country Another earthquake in 1999 prompted additional building codes, but they are not enforced, Stewart said.

"it takes a long time to re retrofit buildings, and it's expensive," Russell said.

Could a similar earthquake happen in the U.S.?

The West Coast of the continental U.S., as well as Alaska, are prone to earthquakes as well, the experts said.

One of the most destructive earthquakes to occur in the U.S. happened in 1906 when nearly 300 miles of the San Andreas fault ruptured, resulting in an estimated 7.9-magnitude earthquake that killed at least 3,000 people in the San Francisco Bay Area. In 1933, the Newport-Inglewood Fault cased a 6.4-magnitude earthquake in Long Beach, California, resulting in extensive damage and killing up to 120 people.

The Long Beach earthquake "taught engineers a lot about how strongly the ground can shake from a 6.5," Hough said.

For decades, California has planned its engineering and building codes based on historical seismicity to survive earthquakes of similar magnitudes, the experts said. In addition, single family homes tend to be more resilient to earthquakes than high-rise apartment buildings, Hough said.

Highways in California, especially bridges and overpasses, have also been retrofitted with steel to protect drivers in the event of an earthquake, Hough said.

"In general, California, the overall resilience is is better than in Turkey," Hough said.

Settlements along fault lines often have high population density because faults tend to present a nice place to live, Hough said. There's typically surrounding water, mountains and more rain, and people will cluster around those regions, she said.

This can prove problematic, because the closer you are to the moving fault, the more shaking you will experience, Hough said.

"You have the settlements right on top of the fold, and then if you have the construction issues on top of that, it's kind of a perfect storm for big damage," she said.

However, biggest earthquakes in the U.S. tend to occur in Alaska.

That region has a low population density, so those quakes are not publicized as much, Stewart said. But since those earthquakes are so large, they can present other rippling effects, such as tsunamis, Hough said.

Although the U.S. would not experience a death toll of similar caliber to Turkey and Syria, there would be severe economic damage, Stewart said.

"Our efforts in retrofitting and engineering to protect lives in Japan and North America is very high, but it is not going to minimize economic loss," he said.