So today I am at a place called Pigeon Bush which is a really extraordinary landform in
the Wairarapa about 50 kilometers northeast of Wellington City. As you can see here with this
drone view there is a long sloping hillside going off into the distance with flat ground
on the one side and a slope on the other. That is the line of the Wairarapa Fault.
Now right behind me here you can see a deep gully coming through that hillside
with a little trickle of water making a small stream coming across just where I'm standing.
It's a very small little riverbed here. We have a very deep cut riverbed with a very small riverbed
just in front of it. A really interesting thing that you can see is just to the side of me there,
is another little stream bed but it has no gully behind it. So it's like a stream bed with no
source. There's nowhere for the water to have reached it and it is now a dry abandoned channel
and there's even a second one some distance further along the slope.
So we have these two dead stream channels and the gully and a place where the modern stream is
flowing through. So what's going on here is that in 1855 there was a huge magnitude 8.2
earthquake along this fault and what used to be the case was that gully was feeding
the next stream bed along. In that earthquake the whole of the land to one side of the fault
was shunted sideways and several meters up to create the situation that we have now.
And even before that last earthquake which was in 1855 there is evidence of a previous one where
the stream has also been offset sometime before the last earthquake. What i'm going to do now is
i'm going to take this tape measure and actually measure the distance between the abandoned stream
channel and the new one to see how far the fault actually moved in the 1855 earthquake.
So i'm going to stop where i think the middle of the gully is from here, very approximately,
so this is not of absolutely accurate measurement - I would say give or take a meter on either side.
But the measurement here says 17 meters. So what that means is in the last earthquake
this fault line ruptured and pushed the land sideways by approximately 16 , 17 or 18 meters
in this area. And it will also have pushed the land up on the far side of the fault by about
a few meters not sure how much exactly. That offset on the Wairarapa Fault is the greatest
earthquake offset on a fault line on land globally on planet earth!
What i'm going to do now is I'm going to take the tape measure in the other direction
to see how far the previous earthquake shunted this fault sideways.
So here I am at the start of the measuring point and now I'm going over to the next gully along.
Okay so now I'm coming across to the previous stream bed and I hope you're super impressed by my
multi-talented filming with a camera and a drone at the same time!
So I think this is about the center of the previous stream bed and it is 14 meters
from that last stream bed. So the earthquake previous to 1855 which would have been
a number of hundreds of years before 1855 shunted the land on one side of this fault at least 14
meters sideways. And then the 1855 earthquake shunted it again by even more than that.
So I hope you're impressed by this world record-breaking fault near Wellington New Zealand!