The GFZ-led study finds that geological stress beneath the Sea of Marmara is rising, particularly beneath the Princes’ Islands, where seismic activity is unusually sparse. Using seismic records from 2007 through the April 23, 2025 M6.2 event, researchers identify an eastward activation trend toward a locked, high-stress segment. They warn a major rupture could have devastating effects on Istanbul’s 15 million residents and call for enhanced real-time monitoring including more borehole stations.
Scientists Warn Rising Stress Under Sea Of Marmara Raises Risk Of Major Quake Near Istanbul
The aftermath of 2023's earthquake. A magnitude 6.2 quake in the Sea of Marmara this April is part of a worrying pattern, say researchers, who see strain migrating towards Istanbul’s locked fault segment. How likely is a larger event? Boris Roessler/dpa
A new study led by the GFZ Helmholtz Centre for Geosciences in Potsdam, Germany, warns that geological stresses beneath the Sea of Marmara — south of Istanbul — are increasing, raising the likelihood of a strong earthquake in the coming years.
The research team, led by Patricia Martínez-Garzón and published in Science, analysed patterns of seismicity from 2007 through the April 23, 2025 magnitude 6.2 event in the Sea of Marmara. Their work highlights a spatial trend of partial activation moving eastwards toward the Princes’ Islands segment, an area that currently shows notably few small quakes.
In 2023, Turkey's level of earthquake readiness was questioned again when more than 50,000 people were killed in a series of quakes in the centre and south of the country. Boris Roessler/dpa
Why This Matters
In regions where faults are releasing stress through frequent small earthquakes, pressure is relieved more often. Beneath the Princes’ Islands, however, instruments record very few events — a pattern the authors interpret as evidence of strong locking and accumulation of large tectonic stresses. If released in a single rupture, these stresses could produce a major earthquake with severe consequences for the Istanbul metropolitan area, home to more than 15 million people and visited by millions annually.
Past Earthquakes And Recent Trends
Notable earthquakes referenced in the study include a 5.2 magnitude event in 2011 and a 5.1 in 2012 in the western Sea of Marmara, a 5.8 on 26 September 2019 in central Marmara, and the 6.2 on 23 April 2025 near the city. The 1999 Izmit rupture (magnitude 7.4) east of Istanbul killed more than 17,000 people; in 2023 a separate sequence of quakes in central and southern Turkey caused over 50,000 deaths, underscoring the country's vulnerability to large temblors.
Researchers fear seismic activity beneath the Sea of Marmara could one day amount to devastating effects on the Istanbul metropolitan region with more than 15 million residents and millions of tourists passing through every year. Ahmed Deeb/dpa
"Our results show a long-term development of partial activation of the Marmara Fault moving eastwards towards the locked Princes’ Islands segment south of Istanbul," said Patricia Martínez-Garzón.
Marco Bohnhoff, a GFZ co-author, added: "The Marmara Fault must be regarded as critically loaded. The April quake brought only negligible relief."
Recommendations
The authors call for substantially improved seismic monitoring beneath the Sea of Marmara, including expanded networks of borehole seismometers and timely public access to real-time data. Enhanced monitoring could improve early warning capabilities, guide preparedness planning, and help authorities prioritise mitigation measures in the most at-risk districts.
For the past decade the GFZ has coordinated the GONAF observatory — borehole seismometer stations — together with Turkey’s disaster agency AFAD. The paper stresses that further investment in offshore and subsea monitoring is essential to reduce uncertainty about timing and size of future ruptures.
Bottom line: Seismic patterns beneath the Sea of Marmara indicate growing, locked stress beneath the Princes’ Islands. Scientists urge immediate strengthening of monitoring systems because a large earthquake south of Istanbul could be catastrophic for its population and infrastructure.
