- The objective of the Building Act and Building Code in respect of any size earthquake is to minimise the risk of harm to people.
- The 1929 Murchison and 1931 Hawke's Bay earthquakes had a profound effect on how we build to survive earthquakes.
- Building codes in 1935, 1965, 1976, 1984 and 1992 were modified to accommodate changes in building materials and better seismic design.
- There are different design requirements for seismic zones in New Zealand and for various categories of building use.
- The Building Act expresses the Government's objective that all old buildings (pre current code) are upgraded so they have strength in excess of 33% of the current seismic loading standard as a minimum. This standard may change following the Christchurch earthquakes and inquiry process/outcomes.
Statutory definitions from the Building Act 2004
122 Meaning of Earthquake-Prone Building
(1) "A building is earthquake prone for the purposes of this Act if, having regard to its condition and the ground on which it is built, and because of its construction, the building –
(a) will have its ultimate capacity exceeded in a moderate earthquake (as defined in the regulations); and
(b) would be likely to collapse causing –
(i) injury or death to persons in the building or to persons on any other property; or
(ii) damage to any other property.
(2) Subsection (1) does not apply to a building that is "used wholly or mainly for residential purposes" unless the building –
(a) comprises 2 or more storeys; and
(b) contains 3 or more household units."
The definition of moderate earthquake is laid down in the Building (Specified Systems, Change the Use, and Earthquake-prone Buildings) Regulations 2005 as:
"… in relation to a building, an earthquake that would generate shaking at the site of the building that is of the same duration as, but that is one-third as strong as, the earthquake shaking (determined by normal measures of acceleration, velocity and displacement) that would be used to design a new building at the site."
Note: The definition of earthquake-prone buildings covers more buildings and requires a higher level of structural performance of buildings than that previously required by the Building Act 1991.