Liquefaction and Ground Failure Hazards in Wellington 1992
Search in document libraryPurpose of the report to review existing data and define the scope of further work needed to assess liquefaction and ground failure hazards in the Wellington Region. This Stage 1 report sets the foundation for detailed mapping and analysis to be comple
Geographic Area Covered:
The report covers five study areas within the Wellington Region:
1. Wellington City
2. Hutt Valley
3. Porirua Basin
4. Kapiti Coast
5. Wairarapa
Summary:
This Stage 1 report initiates a regional assessment of liquefaction and ground failure hazards in the Wellington Region. Liquefaction occurs when saturated, loose soils lose strength during strong earthquake shaking, leading to ground deformation. Such effects can severely damage infrastructure, including buried services, roads, bridges, and buildings.
The report outlines the geological conditions that contribute to liquefaction risk, particularly in areas with soft, recent sediments and shallow water tables. Historical earthquake records show that while Wellington has experienced strong shaking many times since 1840, significant liquefaction effects have only occurred during the most intense events, such as the 1855 Wairarapa earthquake.
Stage 1 focuses on: reviewing past liquefaction events in New Zealand and internationally; identifying existing data sources and gaps; evaluating the susceptibility of soils in the five study areas; recommending methods for further investigation, including field probing and analysis of geotechnical records; and proposing mapping scales and formats for hazard presentation.
The report concludes that Zones 3–5, as defined in earlier ground shaking hazard assessments, are most vulnerable to liquefaction. These zones typically contain loose, saturated sediments and are found in low-lying urban areas. While some data is already available, especially for Wellington City and the Hutt Valley, additional probing and mapping are needed in less studied areas like the Wairarapa.
Stage 2 will build on this foundation by conducting targeted field investigations, compiling and analysing subsurface data, and producing detailed hazard maps and reports for each study area. These outputs will support land-use planning, infrastructure design, and emergency preparedness across the region.