Groundwater responses to the recent Canterbury earthquakes: a comparison

The recent Canterbury/Christchurch earthquakes and aftershocks generated groundwater level responses throughout New Zealand. However, the greater part of damage has been sustained by the city of Christchurch which is built on a layered sequence of artesian aquifers. In this paper we focus on responses in these coastal aquifers. We quantify groundwater responses with a simple model which differentiates between immediate earthquake induced response (spike) and post-seismic change (offset). The most significant feature of our analysis is the consistent pattern of groundwater response to the earthquakes: deeper wells correlate with negative offset and shallower wells correlate with positive offset. This is consistent with the upwards vertical movement of water. We consider the hydrological and engineering consequences.