Seismic activity in the Marmara region has progressively shifted from west to east over the last 15 years, advancing incrementally and increasing stress nearer to the megacity of Istanbul, according to a recent study published in the journal Science.
Led by scientists at Germany’s GFZ Helmholtz Centre for Geosciences, the study notes that smaller, creeping sections of the fault to the west are effectively pushing stress onto the eastern segments nearest to Istanbul, raising the likelihood of a larger rupture.
Though earthquakes are often followed by a period of stress release along a fault, researchers say a magnitude 6.2 earthquake that struck the city of over 15 million people on April 23 did not ease the danger.
Instead, it increased pressure on fault segments south of Istanbul that are currently locked and accumulating energy, putting stress levels unusually high.
According to the researchers, seismic activity began intensifying in the western and central Marmara Sea in 2011–2012.
A magnitude 5.8 earthquake struck off Silivri in September 2019, followed by the April 23 quake, which occurred just to the east of the 2019 epicenter and closer to the city center.
This eastward progression, the authors say, resembles a domino effect along the fault. While the western sections are slowly slipping, the eastern sections remain locked, storing strain that could be released in a powerful earthquake.
This detail matters, researchers say, because ruptures directed toward Istanbul can focus seismic energy toward the city, potentially amplifying ground shaking beyond what the earthquake’s magnitude alone would suggest.
The North Anatolian Fault is a strike-slip fault, meaning the blocks move horizontally rather than vertically. When locked segments finally give way, the result can be sudden and violent shaking.
One of the most concerning findings is a 15–20 kilometer stretch of fault offshore from the Avcılar district of Istanbul that has remained seismically quiet.
This “seismic gap,” lying between the 2025 rupture area and the Princes’ Islands segment, is seen as a prime candidate for a future magnitude-6 or larger earthquake.
Stress transfer from this quiet segment could also trigger the Princes’ Islands fault, which scientists say is fully locked and has been accumulating energy for centuries.
The Marmara Sea is the area facing the highest seismic threat in all of Europe, researchers say.
They warn that the apparent eastward migration of stress increases the urgency of close monitoring, calling for expanded networks of seafloor sensors to track the fault in real time.
