Otago Daily Times
News article 08 May 2015
A neraly eight-year-old report on the expected aftermath of the ''next great Alpine Fault earthquake'' has been doing the rounds on social media this week following the 5.8-magnitude earthquake near Wanaka on Monday.
Facebook and Twitter users have been sharing a link to the report on the Otago Regional Council (ORC) website, and the page has now been viewed more than 34,000 times since Monday's earthquake.
The report summarises talks given in October 2007 by Associate Prof Tim Davies, from Canterbury University, in which he told Wanaka, Queenstown and Cromwell audiences historical patterns of earthquakes and research on the Alpine Fault indicated it was likely to rupture ''very soon'', probably in the next 1-20 years.
The South Island earthquake would be a magnitude 8 or bigger, shake for about two minutes and rupture for up to 400km, Prof Davies said.
He also noted the rupture of another faultline nearby may trigger it, which has caused particular concern on social media this week.
Prof Davies is in the United Kingdom on sabbatical at present so could not be reached for comment on Monday's earthquake and its impact on the Alpine Fault.
However, Dunedin-based GNS Science principal scientist Dr Simon Cox said a 5.8 earthquake was ''very small'' in terms of the stress and movement required to transfer stress to the Alpine Fault, located 50km from the epicentre of Monday's earthquake.
''I would be very surprised if this earthquake has any bearing whatsoever on stresses on faults that far away,'' he said.
It was possible local stress changes had occurred on other faultlines though, such as the Nevis-Cardrona Fault in the Cardrona Valley, about 15km from the epicentre.
Dr Cox said a research paper which came out in 2012 - spanning the past 24 major Alpine Fault earthquakes over 8000 years - had extended the likely timeframe for the next major quake.
The fault's mean recurrence interval was now estimated to be 329 years, plus or minus 68 years.
The last significant South Island earthquake was 298 years ago in 1717.
The Alpine Fault remained New Zealand's biggest seismic hazard and Monday's earthquake and subsequent aftershocks served as ''a timely reminder'' that people should be prepared for the big one.
In his 2007 talks, Prof Davies said when the next major Alpine Fault earthquake struck, Central Otago/Queenstown Lakes residents could expect landslips, lake tsunamis, river delta collapses, breaking dams, floods, debris flows, rock avalanches and severe sedimentation.
Bridges would collapse, roads would be impassible, power would be cut, houses and facilities would be damaged, uncontrollable fires would break out, phones would be dead and many people would suffer disabling injuries.
Prof Davies urged people to store enough essential supplies to be self-sufficient for two to three weeks, carry supplies in their vehicle when travelling, keep a store of construction and weatherproofing materials on their property and identify and strengthen high-risk parts of their property.
Otago Civil Defence Emergency Management Group (CDEM) public information manager Peter Taylor said the top six centres for views of Prof Davies' online report this week were: Auckland, 8948; Christchurch, 8504; Queenstown, 2553; Dunedin, 2128; Wellington, 1760; and Invercargill, 462.
Mr Taylor said Otago CDEM - made up of the region's councils - was considering another tour by a specialist to talk about the newest research on the Alpine Fault.
The tour would be part of a range of activities to promote New Zealand's Shake Out earthquake drill on October 15.