Home' Hastings Mail : June 14th 2011 Contents 11
HASTINGS MAIL, JUNE 15, 2011
Designer style in any colour you like
backed by a 15 year warranty
Call Robert NOW
06 872 7100
15 Hill Road, Bay View, Ph: 836 6298
Free registration for 12 months*
Cores and effect in the quake zone
By CAROLYN VEEN
Ground-breaking work: Associate
Professor John Townend from Victoria
University's School of Geography,
Environment and Earth Sciences, talks
about the science of earthquakes.
In the zone: Heretaunga St after the 1931 earthquake.
As the magnitude of an earthquake only
becomes clear in the wake of a quake, it's
not surprising that even the smallest of
tremors can set the knees trembling,
because no-one knows the potential.
During a recent visit to Napier, Pro-
fessor John Townend, who co-leads the
Deep Fault Drilling Project in the South
Island, spoke of the subduction zone
beneath our feet, and how current
research in the Alpine Fault is already
unearthing fresh knowledge.
In Hawke's Bay and the whole of the
Eastern North Island, the Pacific Plate is
going down beneath the Australian Plate,
and like with the Alpine Fault, we
haven't seen it produce big subduction-
zone earthquakes that produce the
Napier earthquake and other big quakes,
in historic times, but we're still trying to
work out whether it produces these really
big ones, and if it will in the future,'' said
Research projects are greatly aided by
quite a lot of new infrastructure that's
been built over the last few years in New
Zealand, Japan and elsewhere, and all
sorts of equipment is now operating in
real time, so we have an absolutely
unprecedented view of what's going on.
The Christchurch and Japan
earthquakes were, sadly, good examples
of devastating ones that have been very
We will now be able to tease apart
what's going on.''
The ground-breaking work of drilling
deep into the South Island's Alpine Fault
has brought fresh knowledge to the sur-
face, giving scientists around the world a
better understanding of how large faults
evolve and generate earthquakes.
The Deep Fault Drilling Project is
something scientists have dreamed about
doing for decades. It is big science.
Even having the opportunity to drill
150 metres into a little creek bed, full of
gorse, on the West Coast has been
described as the holy grail of earth
Prof Townend said the location on top
of the Alpine Fault is one of only a few
such sites in the world.
The entire investigation is taking
place in an amazing natural laboratory,''
he said, and this is the first time we've
been able to get into a fault zone below
At 650 kilometres long, the Alpine
Fault is so large it is visible from space.
Phase one of the massive project took
place earlier this year, and the results
While the fault has not produced big
earthquakes since 1700, we know it's a
risk, but we just haven't seen it. We're
drilling into it to work out what the fault-
rocks look like, how they've evolved, what
the pressures and temperatures are and
ultimately what the stresses are acting
on the fault.''
A team of top international scientists
drilled two 150-metre bore holes directly
into the fault at Gaunt Creek.
It's only a tiny creek that feeds into a
big river but it's significant in that a lot
of geology has been done over the years
and it shows how the fault moves, bring-
ing up rocks up from deep within the
crust beneath the Southern Alps and
pushing them out over gravels.
So you've got cooked-up rocks that
have been down to 30 kilometres and are
now being thrust out over gravels that
came down the river in the last few thou-
sand years. So it's completely new --
Scientists collected cores for analysis,
which Prof Townend is analysing for seis-
mic and electrical properties (the resis-
tivity) as well as the rocks' mineralogy,
density and porosity.
This is really important because there
are other data sets that other people have
collected which tell us about the electrical
properties at a depth of 10km, and while
they think they know what the fault
looks like, they don't have real
measurements to interpret. So this is the
first time we've retrieved new, fresh rock
to measure the electrical properties, and
we can give it to the people who are doing
the larger-scale analysis.''
The team also discovered that the fault
line (which is basically an interface
between two types of rock) acts as a bar-
rier to fluid flow.
Faults are varied in width, but the
closer you get, the more munched up the
rock is. One of the interesting things we
found when we drilled through the fault
in two places, was the water pressure on
one side of the fault was higher than the
This showed us that the fault was act-
ing as a seal to fluids -- an impermeable
barrier. The pressure of water is a very
important factor in how faults operate --
just as it does when you're driving your
car on wet road; it's slippery because the
water is acting to reduce the frictional
contact between the tyres and the road.
It's the same with faults; if they have
high fluid pressures within the fault
zone, it lubricates them and they slip
more easily. So understanding what the
fluid pressures in the fault are, and how
it behaves, is very important.''
Water flowing down through the fault
plays a big role in controlling the
temperatures, and the temperatures also
control how the fault behaves in earth-
quakes. So it's all about water pressure,
temperature and the type of rock --
greasy mineral or hard quartz.''
The next phase of the operation
involves drilling down to 1.5km, which is
10 times deeper than stage one, and at
least 10 times as complicated.
We've got mountains and valleys, and
the effect of the mountains is to perturb
the fluid pressures, temperatures and the
fault itself, because the mountain acts as
a big load.
To measure the fault conditions at
great depth you need to get away from
the surface as far as possible. The
mountains stick up about a kilometre, so
we want to go at least 1km down in order
to get below their effect.
We're in the throes of planning stage
two, and if it goes ahead it'll probably be
in about 18 months' time, near Whataroa,
and beyond that we might like to drill
even deeper but it's very expensive,'' Prof
more than 100
by New Zea-
Links Archive June 7th 2011 June 21st 2011 Navigation Previous Page Next Page