A mid-7 magnitude rupture at the central-eastern Marmara Sea section would be likely to propagate eastward towards Istanbul, according to Dr Myrto Papaspiliou, head of International Catastrophe Model Research at Howden Re.
In a commentary in the wake of the April and May 2025 earthquakes in Turkiye and Greece, Dr Papaspiliou noted that the last major rupture along the central Marmara Sea segment of the North Anatolian Fault most likely occurred in 1766. A comparable event today could result in ground motions up to 60 times stronger than the 23 April 2025 quake in Turkiye, and thus a higher seismic risk, she added.
“While it remains impossible to predict when and where a major earthquake will strike, the geological reality is that Istanbul, in particular, remains vulnerable,” she said.
Two earthquakes in short succession – first in Istanbul on 23 April, and most recently off the coast of Crete on 14 May – have highlighted the continued seismic volatility of the Eastern Mediterranean. While these events occurred on separate fault lines and are not connected to each other, they both stem from the same broader tectonic dynamics.
The April event, which was centred on the extension of the North Anatolian Fault beneath the Sea of Marmara, caused ground shaking which remained within design standards for Istanbul. As a result, the frequency content of the motion was not especially damaging to the city’s mid- to high-rise buildings and only caused a limited number of injuries. However, the event highlighted the city’s vulnerability to a 7+ magnitude earthquake, with the impact predicted to be significantly more severe in such a case.
Earthquake preparedness and resilience initiatives in the region
Regional advances in earthquake preparedness and catastrophe modelling, alongside sustained investments in infrastructure, emergency response capacity, and public awareness, continue to change the potential impact of seismic activity.
Dr Papaspiliou said, “However, in Istanbul, while the city has demonstrated notable resilience, older building stock and population density could hamper recovery. Building more supportive infrastructure in high-risk areas, such as Gungoren, G. Osmanpasa, and Esenler will be critical.”
Istanbul seismic risk mitigation and emergency preparedness project
One such major initiative, the Istanbul Seismic Risk Mitigation and Emergency Preparedness Project (ISMEP), run by the Asian Infrastructure Investment Bank, aims to strengthen public buildings like schools and hospitals against earthquakes and improve disaster response capabilities. The project, with a budget of $300m, also aims at establishing emergency communication systems, raising public awareness, and training programmes to improve household and institutional preparedness, and indirectly supporting economic stability in Istanbul.
Dr Papaspiliou said that the ISMEP has been highly successful in achieving significant reductions in vulnerability to earthquakes in Istanbul. The project has attracted substantial additional financing from international financial institutions, enabling it to scale up its efforts. Key factors contributing to its success include a sub-national, multi-sectoral approach, a strong project coordination unit, and effective stakeholder engagement. However, challenges remain in replicating the model elsewhere in Turkiye due to financing constraints and limited government ownership.
Dr Papaspiliou said, “The events of April and May 2025 are timely reminders of the ever-present seismic risks across the Eastern Mediterranean. While recent earthquakes have caused limited damage, the next major rupture may not be as forgiving. Strengthening preparedness and accelerating resilience investments, particularly in urban centres like Istanbul, will be essential to protecting lives, assets, and economic continuity. The insurance sector has a pivotal role to play in bridging protection gaps, deploying advanced modelling tools, and informing smarter risk mitigation across the region.”