Research warns that earthquakes are increasingly migrating towards Istanbul

Researchers analyzing two decades of seismic data have uncovered a striking eastward migration of earthquakes along the Main Marmara Fault in northwestern Türkiye. Historical records stretching back more than two millennia indicate that major earthquakes along the fault beneath the Sea of Marmara region occur roughly every 250 years. Based on this pattern, scientists believe the Main Marmara Fault may already be late in its seismic cycle and could be approaching another major rupture.

The findings come from a research team led by Patricia Martínez-Garzón of the GFZ Helmholtz Centre for Geosciences in Potsdam, Germany. The study involved collaboration between scientists from Germany, Türkiye and the United States, as highlighted by SciTechDaily.

By analyzing rupture behaviour and aftershock patterns across different time scales, researchers identified a sequence of earthquakes above magnitude 5 that has gradually progressed eastward along the fault over the past 15 years. These quakes have affected both creeping sections — areas where the fault moves slowly — and locked sections, where tectonic stress accumulates.

The results provide new insight into how stress has been building along the fault system. Because a remaining locked segment near Istanbul could generate an even stronger earthquake, potentially threatening the megacity of around 18 million people, the researchers stress the importance of continuous real-time monitoring.

The analysis shows that moderate earthquakes have gradually moved eastward toward the locked segment south of western Istanbul. This sequence began around 2011 with earthquakes larger than magnitude 5 and continued over the following years.

The progression culminated in the April 2025 magnitude 6.2 earthquake — the largest event recorded on the Main Marmara Fault in more than 60 years. That quake ruptured roughly 10–20 kilometres of the central part of the fault and involved strike-slip motion. Researchers believe stress transferred from the 2019 magnitude 5.8 earthquake may have influenced the timing of the 2025 event.

The eastward migration of earthquakes began within creeping sections of the fault, including the Western High and the Central Basin. These areas experienced two earthquakes above magnitude 5 in 2011 and 2012, leaving behind a quiet zone about 10–15 kilometres long along the eastern edge of the creeping segment. That previously inactive section later became active during the 2019 magnitude 5.8 earthquake, whose rupture extended about 10 kilometres and partially overlapped with the rupture of the 2025 event.

“Our results show a long-term progression of partial earthquake ruptures moving towards the Istanbul-adjacent locked fault segment there,” says Prof. Dr. Patricia Martínez-Garzón, GFZ Scientist and lead author of the study. “This does not tell us when a major earthquake may happen, but it does indicate which parts of the fault become increasingly critically stressed.”

According to the researchers, the recent earthquake sequence has left a relatively quiet segment about 15–20 kilometres long in the Avcılar area, between the Kumburgaz Basin and the locked Princes Islands segment. Because the 2019 earthquake sequence also began in a similarly quiet area, this zone may represent a potential site for the next moderate or large earthquake.

Scientists warn that if a future major rupture propagates from west to east along the fault, ground shaking in the Istanbul region could intensify due to the so-called directivity effect. For this reason, the study emphasizes the need for dense and continuous monitoring of the submarine fault system beneath the Sea of Marmara.

By Nazrin Sadigova