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Alpine Fault

See also: Alpine Fault Photographic Tour

Tectonic setting of New Zealand: astride a plate boundary which includes the Alpine Fault

Tectonic map of New Zealand

 

New Zealand lies at the edge of both the Australian and Pacific tectonic plates. To the northeast of New Zealand, and underneath North Island, the Pacific Plate is moving towards, and being subducted below the Australian Plate. To the south of New Zealand, and underneath Fiordland, the two plates are also moving toward each other but here the Australian Plate is being subducted under the Pacific Plate.

The Australian and Pacific Plates generally don't move smoothly past each other. They move in a series in a small rapid motions each of which is accompanied by one or more earthquakes (what is an earthquake?). Deep earthquakes under North Island form a well defined band (seismic zone) running northeast from Marlborough through White Island. Shallow earthquakes tend to occur to the southeast of this seismic zone, while the deeper ones occur towards the northwest. The earthquakes form this pattern occur where the Pacific Plate is being subducted under the Australian Plate. This pattern of deeper earthquakes towards the northwest of North Island reflects the northwest dip (or slope) of the boundary between the two plates (the Benioff zone). Conversely, in the southwest of South Island where the Australian Plate is being subducted below the Pacific Plate, the deeper earthquakes occur on the southeast edge of the seismic zone where the Benioff zone dips steeply to the southeast.

Volcanoes

As the Pacific Plate is subducted below North Island, the part of the Australian Plate that makes up the central North Island is stretched and has, over many millions of years, become thinner than normal crust. Water released from the Pacific Plate deep under North Island combines with the hot rock of the Australian Plate at about 100km depth and causes a small amount of that rock to melt. This molten rock rises to the surface through the thinned crust and is either erupted from volcanoes like Ruapehu, Tongariro and Ngaruhoe or sits within the crust and heats it, and the water it contains, up causing geothermal activity around Taupo and Rotorua. The area of volcanic activity is referred to as the Taupo Volcanic Zone (see map above).

South Island Faults

Spacelab photo - South Island

The Alpine Fault is the dominant structure defining the Australian-Pacific plate boundary in the South Island of New Zealand. It runs as a single structure for over 500 km. In the Spacelab photo, it forms the sharp line separating the snow-covered Southern Alps in the east from the low coastal plain bordering the Tasman Sea in the west.

The subduction zone in the north is linked to the subduction zone in the south by a series of very large faults that run through Marlborough (Marlborough Fault System) and down the west coast of South Island (Alpine Fault). The Marlborough Fault System is a series of subparallel strike-slip faults which run northeast-southwest. Relative movement across the Marlborough Fault System is dextral or right-lateral.

Along the Alpine Fault the plates are not only moving past each other, they are also moving towards each other. Here, the main part of South Island is being thrust over the Australian Plate on a bearing of about 250 degrees. This compressional movement is causing the Southern Alps to be uplifted at a rate of approximately 7 millimetres per year forming a high elongate mountain range parallel to the Alpine Fault.

Active research in the Otago Geology Department over several decades has lead to detailed maps of the Alpine Fault and related features. In order to make this information available to the public and researchers we have prepared a series of webpages which are freely available. The map below shows the Alpine Fault, in red, from south of Haast to Hokitika in the north. Each yellow box is a 10 x 10 km area that has it own webpage, maps, cross sections and photos. To access the detailed maps click on the box that you are interested in.
Note: the areas, associated webpages and information will be added progressively so be sure to return and check for updates.

Alpine Fault maps (v1 Legacy maps)

See updated maps and data below.

Click on a yellow square below or the links underneath the map to view a detailed 10x10 km map of the Alpine Fault.


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1. Styx

2. Hokitika

3. Mikonui

4. Waitaha

5. Wanganui

6. Poerua

7. Whataroa

8. Franz Josef

9. Cook

10. Fox

11. Karangarua

12. Makawhio

13. Mahitahi

14. Paringa

15. Windbag

16. Cattle Track

17. Haast

18. Okuru

19. Waiatoto

20. Arawata

Alpine Fault traces (updated 10-2013)

GIS data

Download the GIS data which includes Alpine Fault traces and cataclasite zones in shapefile format and an Alpine fault traces layer file (.lyr) for use with ArcGIS.

Vector map

Download the map in pdf format. This single vector document covers all the traces at 1:50k. Use cropping/clipping mask to show the area you want (for best results -drag pdf file in as a linked file). Download legend separately. North is up, scale can be calculated using metre grid, coordinate system used is New Zealand Transverse Mercator Projection. Refer to v1 for contributors to map areas.

3D Alpine Fault zone stucture around the Waitangi-taona and Whataroa Rivers

Download data, maps and posters that were prepared for the conference poster "Three-dimensional structure of the Alpine Fault zone in the region around the Waitangi-taona and Whataroa Rivers" presented at the Geosciences 2012 conference by R. J. Norris, A. F. Cooper, V. Toy, S. Read and L. Easterbrook.

Current Alpine Fault Research

The Department of Geology has been involved in a detailed study of the Alpine Fault and Southern Alps since the late 1970s. Our research programme is currently funded by FRST in conjunction with the Institute of Geological and Nuclear Sciences, and by the University of Otago. We collaborate with a number of national and international groups, particularly including members of the Earth and Ocean Sciences Department at the University of Liverpool.

Paleoseismology

Researchers involved in this work are Professor Richard Norris, Professor Sean Fitzsimons, Professor Alan Cooper.

Recent and ongoing research projects include:

Mapping of quaternary offsets and paleoseismic trenching in the South Westland area.

Investigation of the record of past seismic events in lake sediment cores - PhD student Jamie Howarth

Structure of the fault zone and detailed investigation of the zone of fault rocks with respect to fault kinematics and mechanisms of deformation

Researchers involved in this work are Dr Virginia Toy, Professor Richard Norris, Professor Alan Cooper.

Recent and ongoing student research projects include:

Mapping of along-strike continuity of the fault rock sequence and construction of a 3D model of the fault zone in the Waitangi-taona River area - MSc student Luke Easterbrook-Clarke

Study of comparative fault mechanics and fault zone weakening processes from ductile to brittle regimes in quartzofeldspathic, mafic and ultramafic protoliths, based in the Cascade region - PhD Student Nicolas Barth

Comparative study of pseudotachylytes in the footwall, hangingwall and fault core in the central Alpine Fault - BSc(Hons) student Sam Ritchie

Investigations of the chemical-mechanical processes involved in generation of shallow coseismic fault rocks and coseismic weakening/localisation - PhD student Carolyn Boulton of the University of Canterbury

Investigations of along-strike variations in deformation mechanisms and kinematics within the mylonite zone - PhD student Edward Dempsey of the University of Liverpool.

If you have any questions about the information on these pages please contact Professor Richard Norris, Professor Alan Cooper or Dr Virginia Toy. Geographic data for the maps used in these webpages sourced from NZTopo Database. Crown Copyright Reserved. Cook Saddle to Docherty Creek

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