MBIE has on their website guidance in respect of Ensuring new buildings can withstand liquefaction effects. (Refer https://www.building.govt.nz/building-code-compliance/geotechnical-education/ensuring-new-buildings-can-withstand-liquefaction-risks/ )

A flow chart in this guidance would seem to recommend that where the liquefaction vulnerability has NOT been adequately characterised (eg it is stated as liquefaction risk unknown) then a site specific assessment to determine liquefaction vulnerability should be undertaken. However, above this flowchart under the heading entitled Consider seismicity risk, MBIE advises that “designers should review the regional seismicity risk to determine whether liquefaction is likely to be a governing consideration in foundation design”.

The four seismic zones are defined in NZS 3604:2011 and where they apply are included in figure 5.4 of this standard. The Building Act 2004, s133AD(1) defines a low seismic risk where the Z factor is <0.15. The Auckland region and north has a Z factor of <0.15 and therefore falls within the legal definition of low risk.

Additionally territorial authorities are required to identify earthquake prone buildings. For areas of low seismic risk, this work needs to be completed by the TA by 1 July 2032 and building owners have 35 years from the date their building is identified as earthquake prone to complete the strengthening work. (Refer https://www.building.govt.nz/managing-buildings/managing-earthquake-prone-buildings/how-the-system-works/#jumpto-seismic-risk-areas-and-time-frames )

Given the legal definition of low seismic risk and the application of the timeframes in respect of earthquake prone buildings it may be concluded that for the Auckland and north regions, liquefaction is not a governing consideration in foundation design and assessment of the risk of liquefaction is not needed.