Note: Where available, the PDF/Word icon below is provided to view the complete and fully formatted document
Disclaimer: The Parliamentary Library does not warrant or accept liability for the accuracy or usefulness of the transcripts. These are copied directly from the broadcaster's website.
Christchurch Earthquake -

View in ParlViewView other Segments

Christchurch Earthquake

Mark Horstman heads to earthquake-ravaged Christchurch and meets the seismologists who are
investigating the fault line that caused the damage.

TRANSCRIPT

Comments

NARRATION

Wherever you look in New Zealand, there's evidence of the shifting foundations under the shaky
isles. This old volcanic crater in the heart of Auckland is a reminder of a fundamental reality.

Mark Horstman

New Zealand is torn between two tectonic plates. Stretching along the spine of the country is the
Alpine Fault. As one plate grinds past the other at four centimetres a year, stresses build up in
the landscape like a tensioning spring.

NARRATION

The country is peppered by tremors and quakes from the North to the South Island and these are just
from the last ten years.

Mark Horstman

When it comes to earthquakes, cities here need to be on constant alert.

NARRATION

The city of Christchurch wasn't a place where the seismic hazard was thought to be severe. But in
less than two years, Christchurch has twice hit the world news with earthquakes stronger than
magnitude six and suffered terrible loss of life. I've come here to learn what it means for New
Zealand's second-largest city to find that it's built on a seismic hotspot.

Mark Horstman

Earthquakes have become part of everyday life here. Over the last eighteen months, in and around
Christchurch, there have been more than ten thousand aftershocks, twenty-three in the last week,
several every day. In fact, there could be another one at any moment. Now while most of those
aren't strong enough to be felt, the impact of the strongest ones mean that entire suburbs have
been abandoned.

NARRATION

Tectonic geologist, Mark Quigley once lived here. His house is one of more than five thousand
bought by the government to be pulled down and returned to parkland.

Mark Horstman

This is yours?

Dr Mark Quigley

Yep.

Mark Horstman

How long has your house got now?

Dr Mark Quigley

Well it's scheduled to be demolished in about a month or so.

Mark Horstman

Oh.

Dr Mark Quigley

So not long. It's been here since 1910, but it's near the end of its life.

NARRATION

One morning he woke to a different world.

Dr Mark Quigley

We had this gentle rolling which then just in seconds, just turned into this incredibly violent
shaking. And the bed was moving around on the floor, and things were falling and crashing. And then
it sort of subsided.

Mark Horstman

What was going on that day, out in the backyard?

Dr Mark Quigley

Well I mean, right when we came out, we could see the liquefaction process in action. So basically,
this fine sand and silt was coming out of vents in a variety of places. In this case, the vents
were all lined up, so there was an array of all these bubbling vents. Sand coming out, cascading
over the sides of these, almost like a volcano erupting.

Mark Horstman

Oh.

Dr Mark Quigley

And the water just surging up over the top.

NARRATION

Liquefaction happens when loose, waterlogged soil is shaken strongly enough to be compacted. As the
ground level drops, a slurry of muddy water is pushed to the surface and the damage flows far
beyond a few backyards. This is the area of Christchurch city, and this is the area affected by
liquefaction.

Dr Mark Quigley

Every time there's an earthquake, in this case above about um, point one-seven G's, or you know,
seventeen per cent of the acceleration of gravity, that is enough to trigger liquefaction in these
properties. In this case we've had eight instances of liquefaction, where the ground shaking has
been of sufficient intensity and duration to cause a sort of liquefaction process.

NARRATION

Unless the water table is pumped out, or the soil stamped down and injected with denser gravel,
each earthquake will refloat suburbs on a sea of mud. Houses are left twisted and broken. Streets
once level with bridges have sunk so close to river level, they face a new threat of flooding.
Forty kilometres west of Christchurch, the lush rural landscape of the Canterbury Plains is quicker
to heal. Even though this was ground zero for everything that's hit the city. On the fourth of
September, 2010, a fault nobody even knew was there generated a magnitude seven-point-one
earthquake, which spawned a swarm of smaller tremors.

Dr Mark Quigley

This really large fault, we call the Greendale Fault. That thing unzipped in this direction here
and it actually dropped this part of the river down about a metre.

NARRATION

Seen from space, satellite radar shows how the forty-kilometre long Greendale Fault shifted the
landscape. One side in blue moved west, the other in red moved east.

Mark Horstman

Has this fence changed any, since the day of the quake?

Dr Mark Quigley

Yeah, well it was straight before, and ...

Mark Horstman

Bit of a dog-leg now.

Dr Mark Quigley

Yeah, as a result of that, you know, there's been about three metres or so of right lateral
displacement. But it's also been, been thrust towards itself, and uplifted about a metre or so here
in this area.

Mark Horstman

Three metres one way, one metre up?

Dr Mark Quigley

Yeah, yeah. This was one of the areas that had the, the maximum amount of vertical offset because
of the orientation of the fault and the way that the rupture occurred.

Mark Horstman

So this little hill here, that's new?

Dr Mark Quigley

Yeah. This was all perfectly flat.

Mark Horstman

Oh yeah, right.

Dr Mark Quigley

All these sort of features have been broken apart by the earthquake.

NARRATION

To discover how dangerous this fault could be in the future, Mark's team looks for evidence from
the past.

Dr Mark Quigley

Because the instrumental record of recording earthquakes in New Zealand is so short, you know, we
have to rely on the geological record to tell us about the return times of major earthquakes on
given faults.

NARRATION

Ground penetrating radar on this sled scans the layers of gravel and sand beneath, to read their
earthquake history.

Sharon Hornblow

Which would in turn tell us that this is an active faultline, that you know, you need to watch out
for in the future. It wasn't a one-off event.

NARRATION

Even if big earthquakes happen here only once every few millennia, this one triggered a rolling
sequence of aftershocks that will last for years to come.

Dr Mark Quigley

In a matter of seconds, ah, probably about forty seconds in total, this network of faults ruptured
here and sent that seismic energy into Christchurch and beyond.

NARRATION

Repeated strong aftershocks literally shake down the suburbs and liquefy their natural soils. But
the problem doesn't end there. Built on reclaimed land at the edge of the city is the Port of
Lyttelton, one of the busiest in New Zealand. The safety of the port's foundations worries seismic
engineer, Brendon Bradley.

Dr Brendon Bradley

We're always taught as engineers to expect the unexpected, but I think from that point of view, it
was highly unlikely that we were going to have an earthquake directly below us.

NARRATION

But that's exactly what happened in February 2011, an aftershock of magnitude six-point-three.

Dr Brendon Bradley

Well the earthquake epicentre was about one or two kilometres north of here, directly under the
hills.

Mark Horstman

That close?

Dr Brendon Bradley

That close. And so basically the ground-shaking here at the port was extremely strong, and
essentially all of the ground has moved out towards the sea here, and you can see where we're
standing here on the wharf, we're actually about one-and-a-half metres higher than the ground just
on the other side. So that's the level that the ground has sunk during these multiple earthquakes.

Mark Horstman

That's tremendous damage for anywhere, let alone a port.

Dr Brendon Bradley

Absolutely.

NARRATION

Despite the damage, the port continues to operate while it undergoes repairs. But the risk remains
that strong ground-shaking will collapse the soil under the wharf again.

Mark Horstman

There are two hundred or so of these seismographs dotted around New Zealand, and three of them just
at this port. Now the country's wired for earthquakes - this is transmitting any strong motions it
picks up in real time. I can see it here on the laptop, and it's telling me the last earthquake
recorded was just a few hours ago, just offshore here, magnitude three-point-six.

NARRATION

The good news for Christchurch is that the aftershocks are becoming less frequent as the focus of
seismic activity moves east.

Dr Mark Quigley

It's continued to migrate offshore, and for us that's a, a good sign because it's moving away from
the main urban centre.

NARRATION

Essentially, Christchurch is built on soft, muddy swamplands surrounded by a large rocky bowl. It's
this geology that can amplify an earthquake.

Dr Brendon Bradley

The waves get stuck in this top layer, and that causes shaking which is a lot stronger, and which
lasts a lot longer. And that's really what we mean when we talk about this idea of a bowl of jelly.
That this basin of sediments wobbles a lot more than the underlying rock which it sits on.

NARRATION

And when shallow aftershocks are amplified by the bowl of jelly, the shaking far exceeds what the
city was built to withstand. The ruined CBD is testament to that.

Dr Brendon Bradley

The strength of the ground motion here in the Darfield earthquake and in particular in the February
earthquake was larger than that which we designed these buildings for.

NARRATION

Even after eighteen months, much of the city is still closed off as the demolition crews finish
what the earthquake started.

Dr Brendon Bradley

If we look here where we are in the centre of the city, then actually this building over here has
to be demolished, this building here, this building over here, this building over here, this
building, and also this building over here.

Mark Horstman

There's a long way to go.

Dr Brendon Bradley

There is. It's going to be a completely new city.

NARRATION

A quarter of the buildings in the CBD were made of unreinforced masonry. Now none remain standing.
For engineers like Brendon, it's an opportunity to rebuild a safer city from the ground up.

Dr Brendon Bradley

The technology has improved so significantly over the last twenty or thirty years, you can now
design buildings for a fraction of the cost more, even less than five per cent more cost, that can
survive these type of earthquake events with essentially no damage. Technology such as base
isolation ...

Mark Horstman

Base isolation, what's that?

Dr Brendon Bradley

So base isolation is essentially where we isolate the structure. We lift it up off the ground, and
we place a material which is largely lead rubber, and when the earthquake shakes and the ground
moves, the structure stays still.

NARRATION

Their hometown may be changed forever, but it still offers these two young scientists reason for
optimism.

Dr Mark Quigley

We have been given an opportunity to make ourselves the world's most resilient earthquake city. Um,
and we, we have some drawbacks, we have some setbacks in the sense of where we're located,
geologically, is not ideal. You know, we know that. We have, we have challenges to deal with.

Dr Brendon Bradley

We shouldn't just be thinking about in ten years, let's get back to where we were before 2010, we
should be aiming for 2100 and saying, you know, let's make something really good. Let's use this
chance to do things that before we weren't bold enough to do.