Istanbul · a scenario, not a forecast
A magnitude 7.5 earthquake on the 104 km of the North Anatolian Fault that runs under the Sea of Marmara, 15–25 km off Istanbul's southern coast, at night. What follows is what published models of ground shaking, buildings and people say would happen, run 200 times to show how sure they are.
Mean of 200 simulated earthquakes; the range below each number holds 90 % of them.
Watch it happen, second by second, for magnitudes 6.5 to 7.7: the animated earthquake →
Shaking is strongest along the southern coast, closest to the fault, and where soft ground amplifies it. Each square is one kilometre; the line in the sea is the rupture.
Shaking fades with distance from the fault
Peak ground acceleration on firm soil (Vs30 = 300 m/s): median and the band holding 68 % of earthquakes, for the two ground-motion models. Dots: every 1 km cell of the city (average over runs).
Who and what sits in strong shaking
Modified Mercalli intensity at each place. VI: furniture moves, weak plaster cracks. VII: damage to poorly built buildings. VIII: partial collapse of poorly built ones.
The city's 1.2 million buildings, by damage
Expected share in each damage state, mean of 200 earthquakes.
The same earthquake, 200 times
Buildings with extensive or complete damage in each simulated earthquake. The spread is the uncertainty of the ground motion models: the same magnitude on the same fault can shake twice as hard.
District by district
Buildings with extensive or complete damage: mean and the 90 % range of the scenario, next to İBB's own estimate of very heavily and heavily damaged buildings.
Where it agrees with İBB, and where it does not
Each dot is a mahalle: heavily damaged buildings per 1,000 in this scenario against İBB's estimate. Dots on the line would agree exactly.
Why buildings fail at different shaking
ESRM20 fragility curves for the three most common building types: the chance of reaching each damage state as shaking grows. Each type is measured at the period it is most sensitive to.
A collapsing building throws debris about half its height into the street. Where less than 3 metres stay open, an ambulance or fire engine cannot pass. In Istanbul's narrow residential streets that happens often; on main roads, which are wide, rarely.
Street length blocked, by road type
Mean and 90 % range over 40 simulated earthquakes.
Travel time to the nearest hospital
Share of residents who can reach a hospital by road within a given time, before the earthquake and with the blocked streets of each simulated earthquake (thin lines).
Rail lines by shaking
Kilometres of track in each intensity band.
Bridges
Mean intensity at the major crossings; the scenario does not model bridge damage.