One hundred and fifty seconds.

That's how long it could take to transform the South Island.

The big quake strikes somewhere deep in the Fiordland wilderness, erupting with a magnitude 7.9 mainshock.

The ripples roll north, roaring beneath the West Coast at a blistering pace of 4km per second.

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At just under a minute into the sequence, Haast has been hammered.

At the opposite end of the island, people walking about the streets of Christchurch haven't felt a thing.

That's until the seismic waves punch their way into the Canterbury basin's soft sediment, and the severe shaking starts.

One by

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A quake overdue?

The big shake

Cut off

Getting ready

The Alpine Fault