These earthquakes are along an unmapped 'blind thrust' fault. They are the absolute worst faults in the world. This last earthquake had all the settlements on the footwall, so it wasn't bad, except on deep soil. The next one will be worse.
Napier is all soil, and it's on the hanging wall. If that section goes, it's total wipe-out. Fortunately, the marching order isn't 'cast in stone'. Could be in a couple of years (most likely), or not in our lifetimes. If I were there, I'd start putting everything on screw piles.