As a result of the February 14th Valentines Day earthquake,
we're here in Christchurch and we're part of the GeoNet response.
My role has been to reassess the amount of material
that may have fallen off some of the cliffs.
There's a team of four of us down here and the main objective is to
workout how much volume has fallen off the cliffs in response to the earthquake,
and to work out how much the clifftops have moved backwards
away from the cliff as material falls away.
We can see a lot of damage to the cliff edge,
we can see blocks of rock that are teetering on the edge,
we can see areas of fresh material that has fallen off,
we can see piles of debris at the bottom of the cliffs,
we can see cracks running across the cliffs,
we can see cracks running at the cliff top
and we've seen tension cracks where the ground opens.
What we're seeing with these successive earthquakes
is that the cliffs are getting progressively more damaged as time goes by
and as the earthquakes occur.
So what happens now,
is that in earthquakes that may be similar size to earthquakes that have happened in the past,
we're seeing bigger volumes of material fall off because the ground is more cracked.
What we've seen from this event is that the damage
has essentially been contained to the areas that we've already mapped.
And what it shows to us is the importance of these zones.
The liquefaction team has been working in the northern part of Christchurch in the Kaiapoi area,
mapping the liquefaction that appeared on the surface on the 14th of February.
Mapping the extent of the liquefaction is very useful
to evaluate what is an amount of shaking needed to trigger liquefaction.
We can use helicopters or drones to do a first reconnaissance
of what areas were affected by liquefaction, so we can have an idea
of where to go to map them in the field.
A lot of these features are small and very fragile, so they can disappear fast,
either people want to remove them from their homes or want to clean them out of their driveway.
So for us it's extremely useful that if somebody sees liquefaction,
they bring that information to us as soon as possible.
One of the best ways is just to take a photo and send it to GeoNet.
What we found this time is that some areas,
despite being relatively far away from the epicenter, had substantial liquefaction,
which means that those areas are highly susceptible.
Here in the geodetics team, we monitor the movement of the country
due to the tectonic plate motions surrounding New Zealand.
Since the original Darfield and Christchurch earthquakes,
we have been remeasuring the survey points around Christchurch regularly.
So after the most recent quake, we went back and measured a number of these points again.
This image here shows some preliminary results from that latest survey.
Here is the area surrounding Christchurch.
The colors are derived from satellite imagery,
and the arrows indicate movement at each of the survey marks that we measured with GPS.
This line indicates a point here which has moved a little less than 10 centimetre.
least 14 centimeters this line here
This line here would be around about one centimetre.
Here is an indication of what two centimetres looks like.
So we almost have no movement here and here,
with the largest movement of 9 or 10 centimetres here,
about five millimetres towards the end of Lyttelton Harbour here,
and another five millimetres or so here.
The color on the image is derived from satellite radar images
from before and after the earthquake, and the two images are compared.
It shows in this red area the land has lifted slightly
and in the blue area here it's dropped slightly,
probably in the order of 4 or 5 centimetres up, and 4 or 5 centimetres down.
The blue area that has gone down is just south of the Waimakariri River,
and the red area that has lifted up is around the New Brighton area.