Trinity on Seoul
25 kt fission weapon · South Korea · Population 9,776,000 · Density 16,000/km²
About this scenario
This page calculates what would happen if the Trinity (USA, 1945) detonated over Seoul (South Korea). First nuclear test.
The capital of South Korea and one of the most densely populated megacities in the world. With an urban-core density of about 16,000 people per km², even a relatively small detonation over the city center would affect a large population.
The Trinity delivers 25 kt of explosive yield — 2× more powerful than the Hiroshima bomb. The tables below show calculated effect radii for an air burst (optimized for blast spread) and a surface burst (which produces massive fallout).
Air-burst effects (Trinity over Seoul)
| Effect zone | Radius | Est. affected |
|---|---|---|
| Fireball (vaporization, 100% fatal) | 0.53 km | ~13,879 |
| Severe blast (20 PSI, ~98% fatal) | 1.39 km | ~81,891 |
| Moderate blast (5 PSI, ~50% fatal) | 2.98 km | ~174,266 |
| Light blast (1 PSI, glass injuries) | 8.48 km | ~158,244 |
| 3rd-degree thermal burns | 2.51 km | — |
| 2nd-degree thermal burns | 4.49 km | — |
Estimated total fatalities: ~270,036 · Estimated total affected (inside 1 PSI light-blast radius): ~3,611,150.
Surface-burst effects (with fallout)
A surface burst trades blast spread for radioactive fallout — much smaller blast radii but a large lethal fallout plume drifting downwind. This is what would happen if the Trinity struck ground level rather than detonating optimally above Seoul.
| Effect zone | Radius (surface burst) |
|---|---|
| Fireball | 0.42 km |
| Severe blast (20 PSI) | 0.77 km |
| Moderate blast (5 PSI) | 1.64 km |
| Light blast (1 PSI) | 4.66 km |
| 3rd-degree thermal burns | 1.50 km |
| Lethal fallout zone | ~43.5 km |
Run this scenario in the simulator
See the actual blast zones overlaid on a map of Seoul with population-density-based casualty estimates updated in real time as you move the detonation point.
🎯 Open this scenario on the mapTrinity on other cities
Other weapons on Seoul
FAQ
What would happen if the Trinity detonated over Seoul?
In an air burst over Seoul, the Trinity (25 kt) would produce a fireball about 0.53 km in radius. The 5 PSI moderate-blast zone — where most residential buildings collapse — would extend to 2.98 km. Light blast damage and shattered windows would reach 8.48 km. Given Seoul's urban density (~16,000/km²), this scenario yields an estimated 270,036 immediate fatalities and about 158,244 additional injured.
How many people would die in Seoul from a Trinity strike?
An air burst of the Trinity over Seoul could cause an estimated 270,036 immediate fatalities and 158,244 additional injuries. The fireball alone (radius 0.53 km) would kill approximately 13,879 people; the severe-blast zone (20 PSI, radius 1.39 km) would add 81,891; the moderate-blast zone (5 PSI, radius 2.98 km) would add 174,266 more. Real numbers depend heavily on time of day, sheltering, weather, and altitude of detonation.
What is the blast radius of the Trinity on Seoul?
For an air burst over Seoul: fireball 0.53 km, severe blast (20 PSI) 1.39 km, moderate blast (5 PSI) 2.98 km, light blast (1 PSI) 8.48 km. Thermal radiation causes 3rd-degree burns out to 2.51 km. A surface burst would shrink the blast radii by roughly 40 percent but generate massive radioactive fallout extending ~43 km from ground zero.
Is the Trinity bigger than the bomb that hit Hiroshima?
The Hiroshima bomb (Little Boy) had a yield of about 15 kilotons. The Trinity at 25 kt is 2× more powerful than the Hiroshima bomb.