Progressive eastward rupture of the Main Marmara fault toward Istanbul

The Main Marmara fault (MMF) in northwestern Türkiye poses the highest seismic risk in broader Europe. The 2025 moment magnitude (M_W) 6.2 event was the largest earthquake along the MMF in >60 years. We integrated observations from multiple temporal scales including the decade-long evolution of M > 5 earthquakes, their rupture dynamics, and aftershock patterns. We show a series of eastward-propagating M > 5 events and a gradual eastward partial rupture of the MMF over the past ~15 years. The seismically active portion of the fault includes creeping and transitional segments with some of the most recent seismicity located near the presumably locked Princes' Islands segment south of Istanbul that has the potential to generate a M ~7 earthquake. Our analysis highlights the necessity of real-time monitoring of this part of the MMF.