What would happen if a nuclear bomb hit central Seoul?

Annie Jacobsen's incredible book "Nuclear War: A Scenario" makes you wonder why there's a nuclear debate in Seoul

Seoul, one of the most densely populated cities in the world, is home to over 9.7 million people in its core and 26 million in the greater metropolitan area. A nuclear detonation in the heart of the metropolis would bring unprecedented devastation, transforming the city into a wasteland of destruction and despair.

By examining the blast effects kilometer by kilometer, we can gain a glimpse of the human, environmental, and infrastructural toll this catastrophe would inflict.

When a nuclear bomb explodes, its destructive power is measured in terms of a fireball, a shockwave, intense heat, and deadly radiation. The effects on the population and infrastructure are determined largely by their distance from the blast’s center, or "ground zero."

Let's assume the detonation of a 1-megaton nuclear bomb in central Seoul, around Gwanghwamun Square, for illustration. The damage can be divided into specific zones, extending outward from ground zero.

0–1 Kilometer: Ground zero and total annihilation