Alpine Fault – Page 2 – Out There Learning

Stepping Over the Boundary

Leave a Comment / Earth Science, Julian's Blog / Julian Thomson / Active Fault, Alpine Fault, Field Trip, GeoTrips, Landform, Metamorphic

This is a classic view of the Southern Alps from Lake Matheson on a still morning, showing the high peaks of Mount Tasman and Mount Cook.The Alpine Fault runs along the foot of the steep rangefront, extending right up the West Coast of the South Island. The mountains are therefore part of the Pacific Plate and all the flat land in front, made up of glacial outwash gravels, is on the Australian Plate. This graphic shows the Alpine Fault as a very distinct line dividing the high mountain topography to the East and from the coastal lowlands along the West Coast. Arrows show the horizontal directions of fault ruptures along the fault, but there is also a vertical component that is pushing up the Southern Alps. At Gaunt Creek near Whataroa, you can get right up close to a cliff exposure of the Alpine Fault. The pale green rocks in the foreground have endured being crushed and uplifted along the fault line. They have been altered into what is known as cataclasite, consisting of clay and lots of crushed rock fragments.You can visit this location by checking out our GeoTrips website here: www.geotrips.org.nz/trip.html?id=57 The low angled line of the Alpine Fault is very distinct on the right side of the photo, with the metamorphosed cataclastic rocks that have been uplifted from kilometres down in the crust being pushed over the much younger gravels to the West (right). You really can put your finger on New Zealand’s plate boundary here! The Pacific Plate is on the upper left, thrust over ice age gravels of the Australian Plate on the right hand side of the image. The photo gives a good impression of the nature of the crushed rocks. A more distant view of the cliff section from the creek shows how the uplifted rocks have over-ridden the gravels which are about 15 to 16 thousand years old. The two white arrows show the line of the fault. A short distance away is the Deep Fault Drilling Project (DFDP1) Observatory that was set up after two boreholes were drilled here in 2011. The fault is dipping at about a 40 degree angle, and the boreholes were positioned to intercept it at around 100m depth. Instruments down the boreholes include seismometers and other sensors that have been installed to better understand the physical conditions along the fault as it extends down below the surface. For a bit more background to the DFDP have a look at this previous post from 2011

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The Deep Fault Drilling Project

Leave a Comment / Earth Science, Julian's Blog / Julian Thomson / Active Fault, Alpine Fault, GeoPhysics, Whataroa

The Deep Fault Drilling Project begins its first phase of drilling in the next few days. In this video Rupert Sutherland tells why scientists want to drill into New Zealand’s huge Alpine Fault.

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New Zealand’s Alpine Fault

Leave a Comment / Earth Science, Julian's Blog / Julian Thomson / Active Fault, Alpine Fault, Natural Hazards

For the latest on the Alpine fault drilling visit Rupert’s Blog This NASA photo of the South Island of New Zealand shows the green of lowland vegetation contrasting clearly with snow in the mountains of the Southern Alps. The straight edge of the mountains is the line of the famous Alpine Fault. This fault is the boundary between the Pacific and Australian tectonic plates which are sliding past each other in this region at an average rate of about 40 mm per year. The Alpine Fault is a globally significant feature and similar in character to the San Andreas Fault in America or the North Anatolian Fault in Turkey. Every 200 – 400 years the plate movement is accomodated by a violent earthquake of about magnitude 8, and dislocation along a segment of the fault of roughly 8 metres. The last big earthquake rupture occurred in 1717 AD. Most of the fault movement is sideways, but a portion of it is vertical, and has uplifted the mountains on the eastern side to reveal exposures of the rocks along the fault that have been buried and altered over millions of years. The second image shows a slice of this metamorphic rock with white streaks of quartz, black mica and a red garnet crystal that is about 5mm across. Rupert Sutherland at GNS Science is one of the leaders of the Deep Fault Drilling Project (DFDP) which is about to drill into the Alpine Fault. Many other research organisations are involved in this very large, multi year project. To listen to a short radio interview of Rupert talking about the project go here. From next week, the DFDP project will start by drilling two shallow (150m) boreholes through the fault near Whataroa on the West Coast. Rocks will be sampled and analysed and instruments will be left in the ground as part of a long term monitoring programme. In future years this reasearch will be extended by drilling down several kilometres. In the photo of Rupert he is holding a specimen of fault breccia – a bit of rock that has been fragmented by rupturing of the Alpine Fault. In the close up image you can see how the rock is broken up. The dark patches are where some of the rock was melted and then solidified again in the spaces between the fragments.

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