While the “No Man’s Land” storyline from the comics was triggered by a massive earthquake, Jeremiah was mostly to blame for Gotham’s live-action version.
With the city’s kaboom-ability factor potentially up for testing, the government naturally evacuated the city, which is exactly what needed to happen in order for the grand razing.
After seeing that Jeremiah had already planned on his flip-flopping followers flip-flopping on him at a certain point (ending in their crispy deaths), it was no surprise that the studious villain would have a back-up plan for the initial bomb scheme.