New Zealand ShakeOut 2022
ShakeOut is our national earthquake drill and tsunami hīkoi.
This year we are all practicing our #GetReady skills on 27 October at 9:30am.
This #GetReadyMonth our experts are answering your earthquake questions
Kids Ask An Expert - Why do we have earthquakes?
Our earthquake expert Jonathan Hansen explains
Kids across New Zealand have asked us, "why do we get earthquakes", "why do we have so many", and "does the Alpine Fault really rupture every 300 years?"
Kids Ask An Expert - How many earthquakes in New Zealand?
Our expert Emily Warren-Smith answers the big question
Learn from our experts Jonathan Hansen, Emily Warren-Smith and Rob Langridge as they shake out the facts on all things earthquake.
Our expert Rob Langridge answers your questions transcript
What causes the Alpine fault line to rupture every 300 years? And why is it so regular?
It's a really cool question, and I love your spirit.
The Alpine fault is the major plate boundary fault line in the South Island, and as such it has a really fast rate of motion. So we we've done research on the Alpine fault in Fiordland. It's some special study sites.
We've found that the Alpine fault has had something like 24 major earthquakes in the last 8000 years. And their occurrence time or the repeat time between those earthquakes is around 300 years.
It's actually quite regular. So almost like clockwork.
Every 300 years or so, the alpine fault is having a major earthquake.
So every year, the Alpine fault accrues about 30 millimeters of strain across it. If you add that up year by year, you get centimeters in centimeters and meters and meters.
And after about 300 years, the Alpine fault has actually accrued about nine meters of strain across it.
That means, though, that the Alpine fault is locked and the rocks around it in the South Island are actually taking up the strain by stretching and moving.
We know this from GPS movements, so we know that about every 300 years the alpine far well of accrued enough strain to have a really big earthquake.
Now, why is that so regular? It just relates to the strength of the rocks itself. And then after they've sustained enough strain, they will actually break or the rocks in the fault zone will break and cause a big earthquake.
So many, many faults in the South Island undergo strain.
And you can imagine it like this rubber band that if I stretch it, there's strain going on and eventually that rubber band would break. Now, this what I'm showing you now would be a slow moving fault.
Just imagine if we sped that up by about 30 times and had a 30 millimeter per year fault like the Alpine fault.
You've got that.
And if I was strong enough, that rubber band would have broken that. Basically, the rate of movement or the rate of strain on the Alpine fault is much, much higher than most other fault lines in the South Island.