A magnitude 6.1 earthquake that rattled western Türkiye on Aug. 10 has stirred fresh fears in Istanbul, a city of more than 15 million people that has lived under the shadow of a “big one” for decades.
The quake struck at 7:53 p.m. local time in the Sındırgı district of Balıkesir province, flattening 16 buildings and killing one person, according to officials. Tremors were felt in Istanbul, more than 200 kilometers away, and aftershocks measuring between 2.0 and 4.0 have unsettled residents across the Marmara and Aegean regions.
For many, the shaking brought back memories of April 23, when a 6.2-magnitude earthquake hit Istanbul and the wider Marmara region, and of the catastrophic 1999 quakes in Gölcük and Düzce that killed more than 18,000 people. The recurring tremors have left Turks asking the same question: Is Istanbul still at risk of a major quake?
One of Türkiye’s best-known earthquake experts, Professor Şener Üşümezsoy, says the worst may already be over for the city.
“The only fault line that carried a serious risk for Istanbul — the 25- to 30-kilometer segment between the Silivri and Kumburgaz basins — ruptured in April,” Üşümezsoy said in an interview on Aug. 14. “With that fracture, there is no remaining fault in the Marmara Sea that can trigger a devastating earthquake directly beneath Istanbul.”
Üşümezsoy explained that this segment had remained unbroken since the 1912 Marmara Island quake, which registered at magnitude 7.4. Later quakes, including a 6.8 in Gökçeada in 2014, ruptured other parts of the same fault system. The April 23 Istanbul quake, he said, closed the last gap.
But he cautioned that the Marmara region as a whole is not free from danger.
“The fault line running from Çınarcık to Esenköy, along the Yalova coast, still carries risk,” he said, noting that it has produced large quakes in 1509, 1719, 1766, 1894 and 1999. He also listed the Yenice-Gönen fault, dormant since 1953, and the Bandırma-Sarıköy belt, last ruptured in 1737, as potential sources of strong earthquakes.
By contrast, Üşümezsoy rejected the idea that faults near Avcılar or the Princes’ Islands — often cited in media reports — are active threats. “The Adalar Fault is a dead fault,” he said. “No aftershocks, no bathymetric evidence.”
Üşümezsoy also claimed he had foreseen the Aug. 10 Sındırgı quake. The region, part of the Menderes massif, has a pattern of ruptures stretching back decades. “It is like playing piano keys in sequence,” he said. “Demirci in 1968, Gediz in 1971, Simav in 2014 — and now Sındırgı.”
Despite the timing, he denied any connection between the Istanbul and Balıkesir earthquakes. The North Anatolian Fault, which runs east to west across northern Türkiye, is a compressed system, he said, while the Aegean region is shaped by the stretching of the Aegean Plate. “They are driven by different tectonic processes,” he added.
For Istanbul residents long accustomed to dire warnings about seismic risk, Üşümezsoy’s analysis offers a measure of relief. Still, he stressed that Türkiye’s southern and western Marmara coasts remain vulnerable.
“Earthquakes are not finished,” he said. “But Istanbul itself may no longer be the epicenter.”