An earthquake happens when two plates deep in the ground grind together, sending one above the other, creating shaking in the world above. Big movement can create catastrophic damage and send cities into a state of emergency. New Zealand is on the edge of a ring that gets plenty of earthquakes.
People get pretty scared during an earthquake. Some earthquakes can be near harmless for people but some can kill hundreds. Alot of homes will be damaged in a big earthquake, leaving people without shelter. Those people will have to move to an emergency centre where they will be safe. In really bad situations, big sport stadiums and other places are used as massive shelters. Even if homes stay intact, people still need sewage, water and electricity.
Buildings can vary in how earthquake proof they are. The bad ones, especially, can crumble under the force of a huge earthquake. Fronts of old buildings can easily fall off their foundation while the newer back half of buildings that have been rebuilt, will still be standing. In a huge 7.9 quake, even some new stronger buildings could fall. But some tall skyscrapers have things called dampers that reduce the impact of earthquakes. The only good thing about falen buildings is builders will get lots of work. For a standing building, the last thing wanted is a red sticker that renders the building unsafe.
In an earthquake, roads and railways can be affected. Railways can buckle making it impossible to drive trains. Lots of things can happen to roads, making it even harder to move around. Firstly, while the plates move underground, roads can separate above ground. As well as move sideways, roads can move vertical, making the road like a ramp. A major concern for both roads and railways is sinkholes. Tracks can be swallowed and roads can fall away. What would be worse is an entire house or person falling into one.
Three highly important things are sewage, clean water and electricity. Humans can survive a few days without water but could easily get dehydrated. Sewage is important when you go to the toilet. No sewage means no toilet. A fear during an earthquake is that water is contaminated by sewage which means boiling water for three minutes. That brings in the third thing-electricity which you need to boil the water. In the dark, electricity can be used to light up your house. What if you couldn’t find your way around? So it is important to keep spare water and a generator.
So a big earthquake in a big city would mean a very big disaster. All we can do is prepare and trust in God.