James Muirhead

Any fault line that has moved in the last 125,000 years we would call active and has the potential for future activity.

What I like to say is that we should probably be alert but not alarmed.

So the Mangatangi Fault is positioned in the southern end of the Honua Ranges.

We've been trying to address the question because there actually have been recognised a lot of fault lines around Auckland, but one thing it doesn't answer is this question, are they active?

Have they moved in the last 125,000 years?

That's how we would classify a fault line, as active.

So, for the Mangatangi Fault to address this question, what we want to find are layers of the earth that actually cross this fault line and then get displaced by them or moved across that fault.

And then the next step for us is to then get an age of these layers and we used radiocarbon dating.

Once we get an age of those layers and we know how much they moved, we can then get an idea of when there's been earthquakes in the past.

And from there is to then think about how big was that earthquake?

To answer that, we actually just look at the size of the fault line.

Basically, how large a fault is will determine how much energy it can store, and that will determine the maximum amount of energy it can release during an earthquake.

So with the Mangatangi fault, based on its size, we're looking at about a 6.8 magnitude earthquake if the whole fault line were to rupture in a single earthquake event.

Yeah, so how much damage it does will depend on a few things.

Firstly, how deep did the earthquake nucleate initially from?

If it's really deep in the Earth's crust, the effects will be less at the surface of the Earth.

The other question is, what type of rock is it travelling through across the Earth?

And then additionally, how close are towns and infrastructure to that fault line?

So

In Auckland, we have the Pukekohe region, Drury, places like Takanini, that are situated quite close to the Mangatangi Fault.