Istanbul moves to protect architectural marvel as earthquake threat intensifies

Turkish engineers and cultural heritage experts are working to reinforce the Hagia Sophia Grand Mosque’s vulnerable structural elements, particularly its asymmetrical dome supports, using advanced earthquake simulations to guide their actions, as the megacity faces ongoing seismic threats.

The Hagia Sophia Grand Mosque (Ayasofya in Turkish) has symbolized Istanbul’s endurance for nearly 1,500 years, having withstood empires, devastating quakes, and the test of time. Yet with the growing possibility of a major earthquake, concerns about the monument’s structural weaknesses are increasing, prompting urgent preservation efforts.

“Hagia Sophia is like a patient whose condition becomes more complex with age,” architect Hasan Fırat Diker, a professor at Fatih Sultan Mehmet Vakif University in Istanbul, told the Daily Sabah publication.

Diker serves on the Hagia Sophia Scientific Committee, a multidisciplinary body overseeing the site’s most ambitious restoration in a century. Their mission is to protect the building against future threats while honouring its architectural legacy.

Completed in the sixth century, the Hagia Sophia’s immense dome—among the earliest built on pendentives—has collapsed and been rebuilt repeatedly, with major failures occurring in 558, 989, and 1346. Today, preservation teams are racing to safeguard it for future generations.

Despite this history, the dome has remained intact through major quakes in 1509, 1526, 1766, and 1894, even as surrounding structures failed.

“Hagia Sophia is the heart of Istanbul,” said Diker. “Its continued preservation can be attributed to the efforts of every ruling power – from the Byzantines to the Ottomans and into the Turkish republic era – each doing their best within their economic means to protect it.”

Having served as a cathedral, museum, and mosque throughout its long history, the Hagia Sophia is now undergoing its most extensive restoration since the Republic of Türkiye was founded in 1923.

Initial efforts focused on surrounding Ottoman-era buildings, but now attention is turning to the main structure. “We know its most vulnerable points. Our reinforcement efforts will proceed accordingly,” Diker said.

Focus on supporting central roof

A central issue is the four uneven arches supporting the main dome, weakened by historic repairs and past damage.

“Especially after the last two major collapses during the Byzantine era, the dome and arches had to be rebuilt. But they were made thinner than they should have been, which made the structure more fragile and in constant need of protection,” he said.

One earthquake risk is "hammering," when parts of a structure collide due to insufficient space between them.

“During an earthquake, the two semi-domes built to support the main dome can start to sway. This movement may create hammering, which risks damaging the main dome instead of protecting it,” Diker explained.

Engineers are reinforcing the connection points between the central dome and semi-domes to reduce this threat. “Even though Hagia Sophia has structural weaknesses, we’re not in a position to rebuild it from scratch. Instead, our goal is to intervene using the most appropriate methods for its current state and extend its life span,” he added.

Restoration also involves cleaning the underground areas, restoring the dome and minarets, and addressing long-identified structural issues.

“In previous restorations, especially when Hagia Sophia was a museum, scaffolding around the whole building was often avoided to preserve the visitor experience,” said Diker. “Now, we’re taking a more holistic approach.”

Each phase of the restoration is informed by disaster scenarios, including the threat of a high-magnitude earthquake.

“These earthquake simulations aren’t new – engineers have been studying this since the 1999 earthquake,” he said, noting that current technology and global seismic data allow for much more accurate planning.

Megacity exposed to increased risk

Ilknur Türkoğlu, a cultural heritage expert, noted that Istanbul’s seismic risk is well documented.
“Though Istanbul does not sit directly on a major fault line, its surrounding region is highly active, causing significant earthquakes that have historically caused damage to the city, like the 1999 Gölcük and Düzce earthquakes,” Türkoğlu said.

“With such a large and dense population, the damage and casualties from a similar earthquake today would be far greater,” she warned.

As the former capital of three empires—Roman, Byzantine, and Ottoman—Istanbul holds vast cultural assets, many of which are highly vulnerable.

“Knowing exactly what we have is the first step,” said Türkoğlu, an assistant professor at Istanbul Gelişim University’s Department of Architecture.

“Unfortunately, Istanbul still lacks a comprehensive inventory of its cultural assets, both above and below ground.”

She urged a thorough review of the earthquake resilience of such sites, and immediate reinforcements where weaknesses are found. She added that the aftermaths of the 1999 and February 2023 quakes show the risks of unpreparedness, including the loss or damage of irreplaceable artifacts.

By Nazrin Sadigova