The New Zealand Department of Building and Housing (DBH – now the Ministry of Business, Innovation and Employment, or MBIE) is carrying out a review of earthquake prone building (EPB) policy settings and their implementation. As an input to that review, DBH commissioned this “Risk Framework” document from Tony Taig of TTAC Ltd (a UK based risk expert who has worked extensively in the UK and New Zealand in various natural hazard and other government policy contexts), with support from GNS Science.
Current approaches to managing earthquake risk to buildings and the people in and around them are largely deterministic. New buildings must be built to the National Building Standard (NBS), which requires a specified degree of integrity in a specified earthquake, as laid out in the standard NZS 1170.5:2004. For existing buildings not built to NBS, the law gives powers to local authorities to require owners of EPBs (defined as those not demonstrably capable of withstanding shaking at 33% of the levels specified under NBS) to demolish or strengthen those buildings.
Local authorities must develop an EPB policy in consultation with their local communities; they have considerable discretion as to how they will give effect to their EPB policy. The intent of such a deterministic approach, which is used in many other walks of life besides building risk in earthquakes, is to ensure that levels of risk associated with earthquakes within the design limits of the building are very low. No limits are set or implied on the levels of risk associated with either a) events beyond the design limits, or b) unexpected failures (always a serious possibility in the real world) within the design limits of the building.
This paper considers an alternative approach based on setting policy for building performance in earthquakes in terms of risk. Such an approach starts from consideration of what overall risk (from all possible earthquakes) New Zealand is prepared to tolerate, and how risk might be traded off against other economic or cultural costs and values. Quantifying and valuing risk provides an objective basis for making policy choices – the scale we use to measure risk can also be used to measure the ultimate benefits of policies aimed at reducing it. So we shall address in turn:
- The concept of “risk” and how it can be measured and used in decision making (Section 2)
- The nature and extent of risk associated with buildings in earthquakes, in absolute terms and relative to some other hazards (Section 3)
- EPB policy and risk management factors relevant to it (Section 4), and
- Existing EPB risk management arrangements (Section 5), before discussing
- How best to apply risk concepts to EPB policy and its administration (Section 6).