Alpine Fault

The Alpine Fault is a geological fault, known as a right-lateral strike-slip fault, that runs almost the entire length of New Zealand's South Island. It forms a transform boundary between the Pacific Plate and the Indo-Australian Plate. Earthquakes along the fault, and the associated earth movements, have formed the Southern Alps. The uplift to the southeast of the fault is due to an element of convergence between the plates meaning that the fault has a significant high-angle reverse oblique component of its displacement.

The Alpine Fault is believed to align with the Macquarie Fault Zone in the Puysegur Trench off the southwestern corner of the South Island. From there, the Alpine Fault runs along the western edge of the Southern Alps, then splits into three parallel faults north of Arthur's Pass, merging into the Kermadec-Tonga Subduction Zone in the Hikurangi Trench off the coast of the North Island.

Average slip rates in the fault's central region are about 30mm a year, very fast by global standards.

Historic earthquakes

The Alpine Fault and its northern offshoots have experienced sizeable earthquakes in historic times:
* 1848 - Marlborough. Estimated magnitude = 7.5.
* 1888 - North Canterbury. Estimated magnitude = 7.3.
* 1929 - Arthur's Pass. Estimated magnitude = 7.1.
* 1929 - Murchison. Estimated magnitude = 7.8.
* 1968 - Inangahua. Estimated magnitude = 7.1.
* 2003 - Fiordland. Estimated magnitude = 7.1.

Major ruptures

Over the last thousand years, there have been four major ruptures along the Alpine Fault causing earthquakes of about magnitude 8. These occurred in approximately 1100, 1450, 1620 and 1717 AD, at intervals between 100 and 350 years. The 1717 quake appears to have involved a rupture along nearly 400km of the southern two thirds of the fault. Scientists say that a similar earthquake could happen at any time as the interval since 1717 is longer than between the earlier events. [http://www.nzherald.co.nz/section/story.cfm?c_id=1&ObjectID=10397752]

Large ruptures can also trigger earthquakes on the faults continuing north from the Alpine Fault.

ee also

*Earthquake
*Plate tectonics
*Seismology
*Earthquakes in New Zealand

References

*Robinson, R. (2003). Potential earthquake triggering in a complex fault network: the northern South Island, New Zealand. "Geophysical Journal International", 159(2), 734-748. [http://www.blackwellpublishing.com/abstract.asp?aid=25&iid=2&ref=0956-540X&vid=159 (abstract)]
*Wells, A., Yetton, M.T., Duncan, R.P., and Stewart, G.H. (1999) Prehistoric dates of the most recent Alpine fault earthquakes, New Zealand. "Geology", 27(11), 995-998. [http://data.gns.cri.nz/bib/abstract.jsp?type=template&id=83344 (abstract)]

External links

University of Otago Geology Department:
* [http://www.otago.ac.nz/geology/af/alpinefault.htm Overview]
* [http://www.otago.ac.nz/geology/features/aftrip/start.htm Virtual Field Trip]
* [http://www.otago.ac.nz/geology/features/earthquake/fj400af.htm Potential effects of major rupture] Institute of Geological & Nuclear Sciences Limited (GNS):
* [http://data.gns.cri.nz/af/detail.jsp Summary from the New Zealand Active Faults Database] (includes a map, photos, and references)
* [http://www.gns.cri.nz/what/earthact/earthquakes/historic.html Map of New Zealand's Historic Earthquakes]
* [http://www.gns.cri.nz/what/earthact/earthquakes/earthquakefaq.html#21 FAQ on Alpine Fault]
* [http://www.gns.cri.nz/news/release/alpf.html Press release, 10 September 1998] Miscellaneous:
* [http://www.natureandco.co.nz/land_and_wildlife/landforms/tectonics/idx_tect.php3 Earthquakes and Tectonics in New Zealand]