Thursday, 24 November 2016

The Kekerengu Fault

Photo Tim Little @ VUW
Whilst there were many faults that ruptured during the recent M7.8 Kaikoura Earthquake, the Kekerengu Fault is perhaps the most awe inspiring in terms of its effect on the landscape and infrastructure. As it ripped through the countryside, it displaced the land to either side by an astonishing 8 to 10 metres sideways and about 2 metres vertically over many kilometres of its length.
Kekerengu Fault offset, J.Thomson @ GNS Science
In places this horizontal offset is even more - up to a whopping 12 m. This is impressive on a global scale. In the first two images here you can see what this looks like where farm tracks have been sliced through at a right angle.

Here is a drone's eye view from above:

Kekerengu Fault,   J.Thomson @ GNS Science
As the trace of the fault passes through different locations, it expresses itself in a number of ways.

Across the river from Bluff Station, it has opened up an enormous crevasse, not unlike the sort of thing that mountaineers often see on a glacier. This will be due to either a slight bend in the fault trace, and/or slumping of the downhill side of the fault where there is a slope.
Kekerengu Fault,   J.Thomson @ GNS Science
Slickensides is the name given to the scrape marks  on the surface of the wall of a fault. Here you can see that they are dipping down at about 28 degrees from the horizontal (towards the south-west). This is useful information to help understand the direction of movement of the rupture, and tells us that this fault moved obliquely (sideways and up).  When we looked across the fault we could see that the land on the far side had moved to the right. It is therefore a 'dextral' or 'right lateral' oblique slip fault.

Kekerengu Fault,   J.Thomson @ GNS Science
Fences are really useful markers to allow measurement of the fault offset, especially when they cross the fault at close to 90 in this photo. Yes - those two lines of fencing used to join up!

Kekerengu Fault,   J.Thomson @ GNS Science

The hillside here appears scarred by a simple knife cut...
Kekerengu Fault,   J.Thomson @ GNS Science
...whereas in other places, the slip is distributed over a broad area of surface deformation. In this case it is likely that the groundshaking helped the hillside follow the call of gravity to spread the deformation over a large area.
Kekerengu Fault,   J.Thomson @ GNS Science
Near to the coast, the Kekerengu Fault tracks across this field towards the main state highway and the railway. Here the fault trace is a mound of huge clods of earth and ripped turf. We call this a "mole track", and it results from some compression rather than extension along this part of the fault trace.

Kekerengu Fault,   J.Thomson @ GNS Science
Not far away, State Highway 1 has been pushed sideways in several pieces...
Kekerengu Fault,   J.Thomson @ GNS Science
and the nearby railway has been pulled so hard that it snapped.
Kekerengu Fault,   J.Thomson @ GNS Science

The fault runs right under this small bridge which is totally destroyed.
Kekerengu Fault,   J.Thomson @ GNS Science

Lots of food for thought and plenty of work ahead for earthquake scientist Russ van Dissen and his colleagues.


  1. Stupendous energy involved in that deformation. One can only imagine what the moment must have sounded like there on the ground.

  2. I'm just astounded that GNS have stated this whole event has had absolutely no effect on the pressure around the Alpine Fault, so much land movement ? !!
    Interesting there's been no Alpine fault pressure readings given ?.

  3. Astonishing energy is found in that deformation. Can you imagine, what the moment must have sounded like there on the ground.

  4. This comment has been removed by a blog administrator.

  5. Everyone needs a little help from time to time. A personal loan can help you pay for that great project or purchase Next. Borrowed from $ 5000 to $ 20,000,000.00 in a single payment and take up to 60 months to pay. A fixed interest rate of 1.9% and no annual fee make it a smart solution for your one-time credit needs.
    -get your loan eligibility in 4 hours.
    -Document decision-making free loan.
    Proof of income - not required for eligibility.
    Test address - not required for eligibility.
    Apply today for us without contact at:
    Phone: 1 336-935-2170
    DO NOT ask for an amount in advance.
    Beware of scammers and scams online.