A review of active fault lines and folds undertaken by GNS Science for Otago Regional Council has revealed a “likely” fault line under Wanaka.
The report, which will be presented to ORC councillors today, reviews the locations and characteristics of active faults, combining previously collected information with the latest data. In total, 48 active or potentially active faults were assessed across the Queenstown Lakes and Central Otago districts.
The fault under Wanaka identified in the report, and classified as “likely”, may be part of the NW Cardrona Fault. This fault was previously thought to have run northeast from the Cardrona Valley through Albert Town to Hawea. Scientists now consider that the fault runs north past the foot of Mt Alpha and beneath part of Wanaka township.
“This new interpretation, while still requiring a more detailed assessment for confirmation, may explain a long-standing geological puzzle,” scientists record in the report. “Relatively young landforms have been offset by ruptures of the NW Cardrona Fault in the Cardrona valley, but there is no indication of fault offset of the somewhat older glacial landforms between Albert Town and Lake Hawea. There is undoubtedly a fault in bedrock extending through that area, but in the present dataset that fault is renamed the Cardrona-Hawea fault…”
The report goes on to explain that a future earthquake rupture of the Motatapu Fault and NW Cardrona Fault that deforms or displaces the lake bed is likely to create a localised tsunami.
“This is also potentially the case with the Wanaka Fault beneath the northern arm of Lake Wanaka, and the Hunter Valley Fault beneath Lake Hawea, although those two faults are assessed as being of low activity, with relatively long recurrence intervals.”
Otago Regional Council Natural Hazards Analyst Dr Ben Mackey said further work was needed to substantiate the findings and any implications for Wanaka.
“Currently, some of the information we have about these faults dates back several decades,” Mackey said. “Since that time, technology has greatly improved, as has the scientific understanding of how faults behave. If it is confirmed that an active fault runs under Wanaka, the new information can be incorporated into community resilience planning.”
Chris Hawker, Director of Emergency Management Otago, said earthquakes have always been a feature of the region’s hazard-scape and encourages residents to visit Emergency Management Otago website and www.happens.nz to prepare for an emergency.
“For any event, earthquake, flood or other, we encourage all households and businesses to prepare to cope without electricity for an extended period, and for water and sewerage systems to be out of action.”
The expected chance of fault rupture and related hazards occurring due to a locally sourced earthquake in the Wanaka and Hawea area “has not markedly altered” according to scientists.