Two major fault lines along the Anatolian Plate have generated a number of big quakes. The initial magnitude 7.8 tremor on Monday morning, which was followed by a magnitude 7.6 quake hours later, had the same magnitude as one that killed about 30,000 people in 1939 in northeastern Turkey. A magnitude 7.4 earthquake struck the western city of Izmit in 1999 when more than 17,000 people died.
Experts say several factors have compounded the seismic event. “One of the reasons why the number of casualties has been so high is the poor quality of the buildings,” Mustafa Erdik, professor at Bogazici University’s Kandilli Observatory and Earthquake Research Institute in Istanbul, told Al Jazeera.
Turkey’s National Earthquake Strategy and Action Plan (PDF) for 2012 to 2023 highlighted how massive and rapid migration during the 1950s led to poorly supervised urban development, making cities “critically vulnerable” to natural hazards.
After the earthquake in 1999, Turkey’s institutions recognised an urgent need to reduce the risks in a quake-prone country, and the following year, legislation was approved to enforce mandatory design checks and construction inspections on all buildings.
Buildings constructed according to earthquake-resistant design codes, however, are still in the minority. “Those that have collapsed date prior to the year 2000,” Erdik said.
Nearly 2,900 buildings across southeastern Turkey had collapsed by 5pm (14:00 GMT), according to the country’s disaster agency.
At least two hospitals, one in Hatay and one in Iskenderun, were among them, said Al Jazeera’s Istanbul correspondent Sinem Koseoglu.
She added the large size of many multistorey buildings was complicating rescue efforts as violent aftershocks were still being registered.
Another reason for the high casualty figures is the time the first tremor hit. It struck as people slept at 4:17am (01:17 GMT) and trapped many under rubble.
Turkish authorities measured another earthquake at magnitude 7.6 at 1:24pm (10:24 GMT) four kilometres (2.5 miles) south-southeast of the town of Ekinozu in Kahramanmaras, where the magnitude 7.8 earthquake hit hours earlier.
Live local media footage showed more buildings collapsing in the town of Malatya during the latest massive quake.
Modern buildings were not the only ones damaged. The Gaziantep castle, which dates back to the Hittite kingdom and was expanded under the Roman Empire, has partially collapsed.
Video posted by local media showed parts of the castle tumbling down to the road below.
The Turkish government has declared a level 4 state of emergency, which includes a call for international assistance as well as the mobilisation of all national forces.
Chris Elders, professor at Australia’s Curtin University, said the depth of the initial earthquake at about 18km (11 miles) also contributed to making it particularly devastating.
At a shallow depth, he said, “the energy that’s released by the earthquake will be felt quite close to the surface with much greater intensity than if it was deeper in the crust.”
Naci Gorur, a seismologist at Turkey’s Academy of Sciences, urged local officials to immediately check the region’s dams for cracks to avert potentially catastrophic flooding.
Syria lacks resources to respond to emergency
In neighbouring Syria, buildings were reported to have collapsed in a swathe along the Turkish border extending from Aleppo and Hama to the Turkish city of Diyarbakir, more than 330km (200 miles) to the northeast.
Humanitarian organisations feared the current death toll in Syria – more than 750 people – could rise as rescue teams are severely underequipped to respond to the emergency.
“The machines are old, and there are not enough excavators to help,” Mey Al Sayegh, spokesperson for the International Federation of Red Cross and Red Crescent Societies, told Al Jazeera.
Tanya Evans, Syria director for the International Rescue Committee, said the quake was “yet another devastating blow to so many vulnerable populations already struggling after years of conflict”.
Initial reports from her staff on the ground indicated that the impact has been devastating in areas where a high number of displaced and vulnerable families are living, just as the country is hit by a snowstorm and temperatures plummet.
“This earthquake will only increase the quantity and severity of needs on the ground,” Evans said.