Alpine Fault Trace

BY JULIAN THOMSON (OUT THERE LEARNING)
Accessibility: EASY
The Alpine Fault Trace runs from lower left towards the hill , J.Thomson / GNS.Science
The northern section of the Alpine Fault runs through this area. Fault ruptures (earthquakes) have displaced river terraces that cross the fault. A wall has been built across the fault scarp to check for movement.
The Alpine Fault trace is a low scarp cutting across calf paddock , J.Thomson / GNS.Science
The Alpine Fault extends as a nearly straight line through the length of the South Island. Whilst it ruptures mainly in a sideways direction, some uplift on its eastern side has given rise to the Southern Alps. At its northern end it divides into several branches that are known as the Marlborough Fault System. These faults take up some of the total displacement caused by plate collision, so the continuation of the Alpine Fault is less active here than further south.
At this locality you can see the surface trace of the Alpine Fault running across some grassy river terraces. A wall was built across the fault here in the early 1960s to see if there was gradual slip along the fault.
Scientists have dug trenches across the fault here to find evidence of past earthquakes that can be dated. This allows them to calculate the slip rate (average longer term movement of the fault) as well as the potential magnitudes of earthquakes when the fault ruptures.
Alpine Fault runs across the image, and through centre of wall, J.Thomson / GNS.Science
It is worth looking at the wall to see how it has stood the test of time. As you can see it has not been damaged due to any fault movement or gradual creep (as of April 2016!), showing that the fault is stuck. In other words, movement will occur suddenly during an earthquake, rather than gradually. Most of New Zealand's major faults are similar in this respect.
If you walk along the trace of the fault near to the wall, and along the scarp towards the gravel road, you may be able to see how the landforms have been moved vertically and sideways along the fault. Using a pencil and paper to make a sketch map can help a lot to clarify which features match up across the fault. Estimate the amount of displacement of different features. Older features will have been displaced more than younger ones. See if you can notice any differences.
Directions/Advisory

The Maruia campsite and car park is about 5 km out of Springs Junction on SH 7 towards Lewis Pass

Normally no particular hazard unless there is an Alpine Fault rupture!

Google Directions

Click here for Google driving directions

Accessibility: EASY

The fault scarp runs very close to the parking area

Features
Active Fault Rock Deformation Landform
Geological Age
Holocene
Zealandia Evolution Sequence
Pākihi Supergoup: 5 million years ago – present
Links
There is more information about this locality and some of the science research at http://juliansrockandiceblog.blogspot.co.nz/2016/02/digging-into-alpine-fault.html And a video about the fault and the wall across it here: https://youtu.be/RrxsmIHake0