Did artesian groundwater contribute to Christchurch liquefaction and lateral spread damage?

Part of the GNS-led, MBIE funded 28917-HAZCHCH-GNS programme.

Redistribution of pore-pressure may enable lateral spreading to develop at a larger scale or continue for extended periods – longer than would otherwise be expected from shaking alone. It may explain Christchurch liquefaction severity, where it is not clear why relatively small earthquakes and aftershocks (e.g. M4.8 of 19 Oct 2010) liquefied the ground, or whether ground subsidence is sufficient to account for volume of ejected sediment and water flooding in the suburbs. It may also explain anecdotal observations of c. 5-15 minute delays in some lateral spreading and ejection of liquefied sediment, which occurred after shaking ceased.

The project will attempt to quantify piezometric responses in the aquifers generated by earthquakes and aftershocks, determining the degree to which aquifers leak and became more “connected”, and the rate of pore pressure dissipation to the shallow water table. We will compare responses with shallow ground conditions defined by geotechnical testing and its behaviour defined by other studies of spectral frequencies and liquefaction distribution. We will then test hypotheses on the redistribution of pressure and/or transport of groundwater into the surficial soils during earthquakes with a variety of numerical models. Our goal is to combine geotechnical parameters with groundwater pressure information, to better understand vulnerability of land to earthquake-induced liquefaction and flooding, and to find empirical relationships that can be used to inform sustainable development on artesian aquifers.

Contact person: Helen Rutter h.rutter@aqualinc.co.nz

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