Integrated Stress Evolution and Multi-Segment Rupture Dynamics of the Main Marmara Fault After the 2025 Mw6.2 Marmara Sea Earthquake

The northern branch of the North Anatolian Fault (NAF), the Main Marmara Fault (MMF), constitutes one of the most critical seismic hazards in the Eastern Mediterranean. This system currently hosts an ~120-km seismic gap bounded by the Mw 7.4 1912 Ganos and Mw 7.4 1999 İzmit earthquakes, and most recently accommodated the Mw 6.2 April 23, 2025 Marmara Sea Earthquake. The 2025 event ruptured the Kumburgaz segment, a key structural transition zone between the partially creeping Central Marmara Basin to the west and the fully coupled Çınarcık Basin to the east. Given the ~260-year seismic quiescence along this region of the MMF, understanding how the 2025 earthquake, together with the 1912 and 1999 events, has modified the regional stress field is essential for evaluating the likelihood and characteristics of a future large Marmara Sea earthquake.

In this study, we construct three complementary quasi-static block models to quantify stress evolution along the MMF: (1) a cumulative coseismic stress transfer model incorporating the 1912, 1999, and 2025 earthquakes; (2) a coseismic model isolating the effects of the 2025 rupture; and (3) an interseismic loading model constrained by GNSS observations. The two models enable a comparative assessment of static Coulomb stress changes on adjacent fault segments, illuminating how recent and historical ruptures collectively influence present-day stress accumulation patterns.

Building upon the quasi-static results, we generate new 3D dynamic rupture simulations using a 1D crustal velocity structure for the nonplanar multi-segment MMF, explicitly incorporating interseismic stress loading, coseismic stress perturbations, and the partially creeping behavior of the MMF. We further benchmark these new simulations against our earlier dynamic models that assumed a homogeneous velocity structure to evaluate the sensitivity of rupture dynamics to crustal heterogeneity and initial stress conditions.

Our integrated modeling framework reveals that, during a potential future large Marmara earthquake, rupture is likely to propagate westward through multiple MMF segments, while arresting near the eastern entrance of the İzmit Fault. New segmented rupture patterns are also observed as a result of using a 1D crustal structure instead of a homogeneous medium, together with the inclusion of coseismic stress transfer. The findings offer important insights into post-2025, post-1999, and post-1912 stress redistribution, fault-segment interactions, and rupture cascade potential across the Marmara region. Collectively, this work advances the scientific basis for earthquake hazard assessment in one of the world’s most densely populated and tectonically active metropolitan corridors.