Liquefaction vulnerability increase at North New Brighton due to subsidence, sea level rise and reduction in thickness of the non-liquefying layer

The Canterbury Earthquake Sequence (CES) of 2010 – 2011 caused widespread liquefaction related land damage to the city of Christchurch. This paper addresses the impact the CES had on the eastern Christchurch suburb of North New Brighton with emphasis on the ground condition at the time of the initial 4 September 2010 earthquake, as well as subsidence caused by the CES, and the future potential for increased liquefaction vulnerability due to Sea Level Rise (SLR). Subsidence at North New Brighton accumulated throughout the CES due to a reduction in volume of the soil profile through liquefaction; and overall settlement due to regional tectonic subsidence. The total amount of subsidence caused by the CES at North New Brighton was as much as 1 m in some places and this has changed the relationship between the position of the ground surface and the top of the groundwater table. A reduction in thickness of the non-liquefying layer has been shown to increase the vulnerability of the soil profile to liquefaction related land damage during earthquake events. As a coastal suburb, North New Brighton is vulnerable to the impact of SLR and this paper considers the response of the groundwater table to rising sea level and the influence this will have on the thickness of the non-liquefying layer and liquefaction vulnerability.