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 degrees.as 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.

A Ruptured Landscape

J,.Thomson @ GNS Science

On the ground in the Kaikoura Quake aftermath:

Following the recent M7.8 Kaikoura Earthquake, a number of teams of scientists have been deployed to survey the geological impacts and assess the potential ongoing risks to people and infrastructure.

This gallery of images shows some of the numerous dramatic impacts of the quake in the coastal area to the north of Kaikoura.

 J.Thomson @ GNS Science

Accessing the area by road involves careful driving. The road surfaces next to many of the bridges have subsided, creating a crack at either end of the bridge:

 J.Thomson @ GNS Science

Slumping has occurred along parts of the highway:

 J.Thomson @ GNS Science

This photo shows the now famous house at Bluff Station that had the mis-fortune to be built directly on top of the Kekerengu Fault. The house was shunted about 7 metres sideways leaving some of its foundations behind.

J.Thomson @ GNS Science 

The house was pushed across its own driveway...

J.Thomson @ GNS Science

The coastal highway and railway have unfortunately been cut through in several places by fault ruptures. This view looking south at Waipapa Bay shows the northern branch of the Papatea Fault crossing SH1 and heading out to sea.

J.Thomson @ GNS Science

This is what the road now looks like on the ground. The fault scarp has been bulldozed to allow vehicle access.

J.Thomson @ GNS Science

A short distance away, the railway line was lifted up and dropped in the grass next to its original gravel bedding.

J.Thomson @ GNS Science

From the top of the fault rupture, you can see that the displaced railway tracks extend for about 300 metres into the distance.

Will Ries @ GNS Science

A few hundred metres further south, the southern branch of the Papatea Fault crosses the road and railway.

J.Thomson @ GNS Science

The earthquake ripped right through the concrete culvert that ran under the road, and again lifted the railway off its bed.

J.Thomson @ GNS Science

From the air, the scarp of the southern branch of the Papatea Fault is seen to extend like a knife-cut across the shore platform. In this image you can sea the uplifted coastline extending into the distance. The total uplift of the area left (east) of the fault is 5 to 6 metres, whilst the area to the right was uplifted by a smaller amount. Water has been ponded up against the new fault scarp.

J.Thomson @ GNS Science

A helicopter view showing the scarp of the Papatea Fault close up (across the top of image). The fault movement is thought to have been mostly horizontal with about 2 metres of vertical uplift in addition.

J.Thomson @ GNS Science

The Papatea Fault scarp is a sheer wall about 2 metres high.

J.Thomson @ GNS Science

Part of the task for scientists is to measure the uplift along the coast. The high and low water marks make a useful reference point that can be surveyed against the new sea level positions.

J.Thomson @ GNS Science

Sadly the raised shoreline stranded innumerable sea creatures that now litter the area amongst the seaweed.

J.Thomson @ GNS Science

Rockfalls have been numerous, and have caused a lot of damage where the road and railway are squeezed up close to the coastal cliffs.

J.Thomson @ GNS Science

The end of the road? The reason why you won't be travelling into Kaikoura from the north anytime soon. This rockfall is at the south end of Okiwi Bay, and there are more slips like this further south.