Past, Present, and Future Liquefaction Hazards at Greenmeadows School, Napier, New Zealand

Hawke’s Bay, a region on the east coast of Aotearoa New Zealand’s North Island, has some of the highest seismic hazards in the country owing to the nearby Hikurangi subduction zone. The major towns of Napier and Hastings were severely damaged by the Ms 7.8 1931 Hawke’s Bay Earthquake, one of the largest the country has ever experienced. Liquefaction features were observed after this earthquake, but liquefaction hazard in the region is understudied. Seismic risk in Hawke’s Bay is compounded by its vulnerability to other hazards that are worsening due to climate change. In February 2023, a severe storm, Cyclone Gabrielle, moved across the region and caused an estimated $8 billion in storm and flooding damages. The interaction between liquefaction hazard and hydroclimatic change is not yet well understood. To better understand this linkage, an ongoing collaborative research project examines several case history locations in Napier; this paper examines one of them, the Greenmeadows School site. This site was selected due to nearby historic observations of liquefaction after the 1931 earthquake. A suite of field tests was conducted to provide a comprehensive understanding of the present hydrological and geotechnical conditions, including seismic refraction, Multichannel Analysis of Surface Waves (MASW), Microtremor Array Measurements (MAM), Seismic Cone Penetration Test (SCPT), and the Direct Push Crosshole (DPCH) test. The combined data set provides detailed insight into the soil strength and resistance to liquefaction. Of particular interest is the depth of groundwater, which significantly influences liquefaction triggering and is subject to change with evolving hydrological conditions due to storms, seasonal fluctuations, or rising sea levels. While this project aims to quantify this by collecting future measurements during the winter season at this site, data collected in the summer provides insights into how partial saturation is likely to play a role in the resistance to liquefaction.