Persistent rupture segmentation of the Main Marmara Fault

The Main Marmara Fault (MMF), a major strand of the North Anatolian Fault beneath the Sea of Marmara, includes a 150 km locked segment that poses a critical seismic risk to İstanbul, a megacity of over 15 million people. Although significant progress has been made in characterizing rupture segmentation along the MMF, the underlying physical controls remain poorly understood. Here, we use seismic cycle simulations to explore the influence of along-strike variations in sediment thickness and temperature on earthquake rupture and recurrence behavior. We construct a three-dimensional rheological model by integrating regional heat flow and laboratory-derived frictional properties for basement rocks and basin sediments. The simulations reproduce key features of the historical seismic record, including the 1766 and 1912 M > 7 earthquakes. A rheological barrier in the Central Basin segment associated with the thick sedimentary cover and a regional thermal anomaly restricts earthquake size and the multiple fault bends influence epicentral locations. Over 10,000 years of simulated seismic cycles, earthquakes do not exceed M 7.3. Earthquake hazard in the Marmara region is controlled by the interaction between fault geometry and rheology, underscoring the need for integrated structural, thermal, and lithological models in seismic hazard assessment. The magnitudes and epicentral locations of earthquakes along the Main Marmara Fault, Türkiye, are governed by fault geometry, such as fault bends, and by rheological barriers like thick sedimentary sequences, according to simulations of 10,000 years of the seismic cycle.