Land in the green zone has been divided into three technical categories. These categories describe how the land in expected to perform in future earthquakes. The technical categories – TC1 (grey), TC2 (yellow) and TC3 (blue) describe the foundation systems most likely to be required in the corresponding areas on the maps. As this is an area wide classification site specific geotech work will be required to determine the actual foundations required for each house in TC3 areas. In some cases this will mean TC2 level foundations will be enough in TC3 areas based on actual ground tests. This approach is common throughout New Zealand. It is important to note that property owners only need to replace their foundations if their house needs to be rebuilt, or requires repairs to the foundations. Otherwise, no further action is needed (until you undertake major renovations that affect your foundations).
Green zone changes: what they mean for you As part of the ongoing information sharing process, CERA has produced a half-hour discussion panel to cover some of the key issues around the Green Zone changes, particularly the new Technical Categories. The discussion is facilitated by CERA chief executive Roger Sutton and involves Reid Stiven from EQC, Malcolm McMillan from the Department of Building and Housing, Mike Jacka from Tonkin and Taylor, and Dean MacGregor from IAG Insurance. This production was put together by CERA and CTV, and was originally broadcast on Maori Television on Saturday 19 November, and CTV on Sunday 20 November, this production was made with technical assistance from TV3.
http://cera.govt.nz/residential-green-zone-technical-categories#green-zone-changes-video