Whangamata fault zone
The Whangamata fault zone is part of the seismically active western Taupō rift-bounding normal wall faults [1] and is associated with the major active Whangamata Fault and Haukari/West Whangamata Fault and several unnamed active faults. Obsidian used by the Māori is exposed along these faults.[4]
| Whangamata fault zone | |
|---|---|
| Whangamata Fault, Haukari/West Whangamata Fault [1] | |
| Etymology | Whangamata Bay, Lake Taupō |
| Country | New Zealand |
| Region | Waikato Region |
| Tectonics | |
| Plate | Indo-Australian |
| Status | Active |
| Earthquakes | June - July 1922,[2] 2001[3] |
| Type | Normal fault |
| Movement | 5 MW+ in 1922 with 1.8 m (5 ft 11 in) displacement[2] |
| Age | Quaternary |
| Volcanic arc/belt | Taupō Volcanic Zone |
| New Zealand geology database (includes faults) | |
Geography
The known active faults in the zone extend north east from Kinloch on the north west shore of Lake Taupō approximately 20 km through the rhyolytic volcanic dome of Ben Lomond[5] to the region of the Mokai Power Station.
Geology
The present western wall faults of the Taupō Fault Belt in this region of active extension by 8 mm (0.31 in)/year ± 2 mm (0.079 in)[1] of the modern Taupō Volcanic Zone have been defined by earthquake swarms such as occurred in 1922 which resulted in a 1.8 m (5 ft 11 in) displacement of the Whangamata Fault[2] and the swarm of 2001.[3] To the north the zone continues as the Thorpe - Poplar Fault and to the south has its structure disturbed and hidden by the Taupō Volcano. The 2001 earthquake swarm is best explained by intrusion into a volcanic dyke.[3]
Risks
These are typical for a fault structure adjacent to an active volcanic caldera filled with a lake, being both tectonic and any associated volcanism and so could be significant. The 1922 earthquake swarm was associated with several earthquakes in the range of 5 to 5.4 MW which caused chimney collapse, land slips, as well as both local and international concern sufficient to impact the tourist industry given the manifest lake shore subsidence and fault displacements.[2] The swarm lasted nine months with total displacement of up to 3 metres (9.8 ft) on the northern shore of Lake Taupō (not just the Whangamata fault zone was involved).[2] As the magma-tectonic interaction of the 2001 swarm may have been from a magma source independent of the Taupō Volcano, relatively small scale eruption associated with the faults would be possible, if a dyke reaches the surface.[3]
Mineral Resources
The extensive and used obsidian outcrops near Kinloch were accessible to the Māori as they were exposed by the Whangamata Fault.[4]
References
- Darby, Desmond J.; Hodgkinson, Kathleen M.; Blick, Graeme H. (2000). "Geodetic measurement of deformation in the Taupo Volcanic Zone, New Zealand: The north Taupo network revisited". New Zealand Journal of Geology and Geophysics. 43 (2): 157–170. doi:10.1080/00288306.2000.9514878.
- Johnston, David; Scott, Brad; Houghton, Bruce; Paton, Douglas; Dowrick, David; Villamor, Pilar; Savage, John (2002). "Social and economic consequences of historic caldera unrest at the Taupo volcano, New Zealand and the management of future episodes of unrest" (PDF). Bulletin of the New Zealand Society for Earthquake Engineering. 35 (4): 215–230. doi:10.5459/bnzsee.35.4.215-230.
- McGregor, R. F. D.; Illsley-Kemp, F.; Townend, J. (2022). "The 2001 Taupō Fault Belt seismicity as evidence of magma-tectonic interaction at Taupō volcano". Geochemistry, Geophysics, Geosystems. 23 (e2022GC010625). doi:10.1029/2022GC010625.
- Moore, PR (2011). "The Taupo obsidian source, central North Island, New Zealand". Journal of the Royal Society of New Zealand. 41 (2): 205–215. doi:10.1080/03036758.2010.529919.
- Stevenson, R. J.; Briggs, R. M.; Hodder, A. P. W. (1994). "Physical volcanology and emplacement history of the Ben Lomond rhyolite lava flow, Taupo Volcanic Centre, New Zealand". New Zealand Journal of Geology and Geophysics. 37 (3): 345–358. doi:10.1080/00288306.1994.9514625.