To setback or not to setback from active faults; the Alpine Fault in the Tasman District, Nelson, New Zealand

Johnston, M.R.

Proceedings of Technical Groups - Institution of Professional Engineers New Zealand 31(1): 75-81


The active Alpine Fault extends through the southeast of the Tasman District in a topographic corridor between St Arnaud and Tophouse. While the fault is generally a conspicuous feature resulting from the offsetting of moraine, fan and other Quaternary deposits, its precise location is generally not known other than that it is commonly within scarps between 20m and 140m wide. It has been recognised by the Tasman District Council that structures should not be built across the fault or within a zone encompassing the fault that will undergo strong ground deformation. Currently the Council has a 10m mandatory setback from the fault, which also lies within a 100m wide fault hazard planning zone. Any proposed development within the zone requires a geotechnical investigation to show that it is more than 10m from the fault. This paper discusses possible refinements to the planning requirements, particularly in reducing the need for a geotechnical investigation unless the development is close to the fault.