Two massive earthquakes that struck southern Turkey and northwest Syria on Monday have killed more than 22,000 people, making the natural disaster one of the worst of the century.

Just hours apart, the quakes ruptured cities and towns across the region and hopes of finding more survivors among the rubble in freezing conditions are starting to fade.

The devastation was particularly deadly because the shocks were both powerful and shallow and also struck a region where few buildings were fully compliant with codes designed to make them more resistant to earthquakes.

The first 7.8-magnitude quake struck a little after 4 a.m. (0100 GMT) about 30 km (19 miles) northwest of Gaziantep, a city of more than 2 million people in southern Turkey.

Nine hours later, a 7.5-magnitude quake struck due north, just one of more than 150 aftershocks to hit the region since Monday.

Monday’s first earthquake created severe shaking across an area about 285 km (177 miles) long according to the U. S. Geological Survey (USGS).

Initial USGS estimates of the surface rupture length – the length of ground visibly displaced by both the 7.8 and 7.5-magnitude quakes along fault lines – stood at almost 300 km (185 miles).

Only three earthquakes have registered above 6.0 on the Richter Scale since 1970 in the area, according to the USGS, though a 7.0 quake hit the region in 1822, killing an estimated 20,000 people.

Turkey lies along one of the most active seismic belts in the world, stretching from the Alps and the Mediterranean all the way to the Himalayas. The country experiences a destructive earthquake on average once every five years, according to the Ministry of the Interior’s Disaster and Emergency Management Presidency.

“Turkey has experienced the deadliest earthquake worldwide four times in the last 50 years, so is no stranger to the deadly consequences of such events,” said Joanna Faure Walker, head of the UCL Institute for Risk and Disaster Reduction in London.

Most of Turkey lies on the Anatolian plate, which is pinched between two major faults along the borders of the Eurasian, and Arabian tectonic plates.

Of the two major faults, the North Anatolian Fault has produced more major earthquakes in recent times than the East Anatolian Fault, where Monday’s quakes struck.

During the 20th century, the East Anatolian Fault showed very little major seismic activity.

“If we were going simply by (major) earthquakes that were recorded by seismometers, it would look more or less blank,” said Roger Musson, an honorary research associate at the British Geological Survey.

The two quakes on Feb. 6 were the first greater than 7.0 along the East Anatolian Fault in the last century.

The earthquakes were powerful and shallow, with the 7.8-magnitude quake centred just 18 km below the surface.

“The combination of large magnitude and shallow depth made this earthquake extremely destructive,” said Mohammad Kashani, associate professor of structural and earthquake engineering at the University of Southampton.

The energy unleashed from shallow earthquakes doesn't have enough space to dissipate before it hits the surface, often causing more destruction than deeper earthquakes.

Earthquakes are usually caused when underground rock suddenly breaks and there is rapid motion along a fault line. This sudden release of energy causes seismic waves that make the ground shake.

There are three types of stress along a fault that can produce earthquakes: normal faults, strike-slip faults and reverse faults.

The East Anatolian Fault is a strike-slip fault.

In those, solid rock plates push up against each other across a vertical fault line, building stress until one finally slips in a horizontal motion, releasing a tremendous amount of strain that can trigger an earthquake.

The San Andreas Fault in California is perhaps the world's most famous strike-slip fault, with scientists warning that a catastrophic quake there is long overdue.

Photos and video from Turkey and Syria showed catastrophic building collapses.

Rescue crews sifting through the rubble pulled a 10-day-old boy and his mother from the ruins of a collapsed building in Turkey on Friday, four days after the initial quake, and dug out several people at other sites.

Hundreds of thousands more people have been left homeless and short of food in bleak winter conditions after their homes were destroyed.

“The photos show that some of the collapsed buildings may have been built prior to modern seismic design code so they might not be appropriately designed and detailed for such a large magnitude earthquake,” said the University of Southampton’s Kashani.

In 2021, researchers from the Middle East Technical University and Hacettepe University in Turkey’s capital Ankara, and the University of Minho in Portugal, modelled the potential damage an earthquake might cause to Gaziantep and catalogued how well prepared the buildings in the area were to survive a large seismic event.

They found that just 11% of buildings were fully built to codes compliant with earthquake resistant design and construction. More than a third of the buildings were built with unreinforced masonry, which is particularly susceptible to seismic damage.

“Many of the buildings in the towns affected are simply not designed to cope with this level of strong shaking, and in Syria many structures have already been weakened by more than a decade of war,” said Bill McGuire, emeritus professor of earth sciences at UCL in London.

Ground shaking is the primary cause of earthquake damage to man-made structures but because it’s difficult to predict the intensity of the shaking, it’s also difficult for engineers to build buildings that can withstand the strongest earthquakes.

Still, certain natural factors in the ground, as well as basic construction techniques and materials, can help reduce the risk that a building will collapse, researchers say.

“Earthquakes cannot be accurately forecast, so prevention of the consequences depends on preparedness and efficient response,” said Carmen Solana, a reader in volcanology at the University of Portsmouth.

“The resistant infrastructure is unfortunately patchy in south Turkey and especially Syria, so saving lives now mostly relies on response.”