Stats House built in known hazard zone
Wellington’s doomed Statistics House sat amid swathes of specifically designated ‘‘hazard’’ areas across the city, prone to high shaking in earthquakes.
While the failure of Stats House in the 2016 Kaiko¯ura quake was blamed on various factors, an official information response from the Greater Wellington Regional Council shows it had been a known hazard area for about a decade before ground was broken at the Centre-Port site.
A 2004 Wellington City Council land use consent for construction of the building shows the site was then designated a hazard – ground shaking – area.
It appears this description came from a 1992 investigation by the regional council.
The investigation gave the same designation to large tracts of the city – including the shoreline from Queens Wharf to Oriental Bay, and parts of Te Aro, Kilbirnie, Lower Hutt, Wainuiomata, and central Porirua. These were identified as ‘‘zone five’’ areas – characterised by ‘‘high to very high amplification of earthquake ground motion, relative to bedrock, and therefore subject to the greatest ground-shaking hazard’’.
Greater Wellington environment manager Nigel Corry said the Stats House land had ‘‘high ground-shaking potential’’.
‘‘What this means is that the ground there has a higher risk from amplified ground motions due to the underlying soils and sub-surface geology. In this situation, loose unconsolidated marine sediments, gravels and other fill were used in the reclamation of the port land from the late 19th to the mid-20th century.’’
The hazard ratings of the Stats House area, and others around Wellington with the same designation, had not changed since the 1990s.
‘‘It is not recommended that the information be used for engineering and construction purposes. Rather, it is intended to flag an area for further investigation in any proposed development.’’
The underlying geology and the potential seismic hazards at Statistics House were recognised and foundations were designed accordingly.
A Ministry of Business, Innovation, and Employment report into the failure of the building found four causes – flexible frames, floor construction, up to two minutes of significant shaking, and localised amplification of the shaking.
‘‘The site conditions were investigated and the geotechnical advice provided was generally in accordance with the standard of practice for this type of building at the time,’’ the report said.
The report shows the land was reclaimed between 1893 and 1901. According to the regional council, other areas around Wellington with high potential for ‘‘amplified ground shaking’’ include the coast from Queens Wharf to Oriental Bay. It also included parts of Te Aro, the Kilbirnie isthmus from Evans to Lyall Bay, central Miramar, and Seatoun.
‘‘Outside of Wellington city, much of Lower Hutt, Wainuiomata and the Porirua CBD are built on loose, unconsolidated sediments at risk from amplified ground shaking and liquefaction.’’
Wellington City councillor Iona Pannett, who has the infrastructure portfolio, said there was no going back on where Wellington had been developed. But information now available on quake risk and climate change meant more care was needed with where was developed in the future.
Centre-Port, which owns the land, would not comment.