A · DocumentedGeophysical

A large earthquake near Istanbul (Marmara)

The North Anatolian Fault runs under the Sea of Marmara, close to Istanbul. Segments of it have broken one after another through the 20th century, and the stretch south of Istanbul has not produced a major rupture for a long time. Türkiye has lived through this: the 1999 İzmit earthquake and the 2023 Kahramanmaraş earthquakes.

The tier rates the quality of the evidence, not how likely the event is.

How it could unfold

1A rupture of the Marmara segment, likely magnitude 7 or more● strong evidence
2Strong shaking in a metropolitan area of over 15 million● strong evidence
3Damage depends overwhelmingly on building quality and enforcement● strong evidence
4Fire, gas and infrastructure failures follow; the response is a test of preparation◐ moderate evidence

Historical anchors

İzmit, 17 August 1999 (magnitude 7.6): between about 17,000 and 18,000 deaths.
Kahramanmaraş, 6 February 2023 (magnitudes 7.8 and 7.5, nine hours apart): at least 53,000 deaths in Türkiye by official figures.

What experts and models say

Source	Statement	Kind
Parsons (2004) ↗	A published recalculation of the probability of an M ≥ 7 earthquake beneath the Sea of Marmara. Estimates are large, in the tens of percent over a few decades, and depend on the model; see the paper for ranges.	PROJECTION

Expert estimates are personal judgements, not measurements, and experts disagree. This site never adds its own probabilities.

Caveat

Nobody can predict the date of an earthquake. Probabilities describe decades, not months.

What you can do

Secure heavy furniture; know your building's condition and your gathering point.
Keep a grab-and-go bag by the door (AFAD and Kızılay publish checklists).

Open the preparedness checklist for this scenario →

Related scenarios

Cascadia megathrust earthquake and tsunami

References

Parsons, T. (2004). Recalculated probability of M ≥ 7 earthquakes beneath the Sea of Marmara, Turkey. J. Geophys. Res. 109:B05304. link ↗