Abstract
The 2016 Mw7.8 Kaikōura earthquake induced groundwater level changes throughout New Zealand. Water level changes were recorded at 433 sites in compositionally diverse, young, shallow aquifers, at distances of between 4 and 850 km from the earthquake epicentre. Water level changes are inconsistent with static stress changes but do correlate with peak ground acceleration (PGA). At PGAs exceeding ~2 m/s2, water level changes were predominantly persistent increases. At lower PGAs, there were approximately equal numbers of persistent water level increases and decreases. Shear-induced consolidation is interpreted to be the predominant mechanism causing groundwater changes at accelerations exceeding ~2 m/s2, whereas permeability enhancement is interpreted to predominate at lower levels of ground acceleration. Water level changes occur more frequently north of the epicentre, as a result of the fault’s northward rupture and resulting directivity effects. Local hydrogeological conditions also contributed to the observed responses, with larger water level changes occurring in deeper wells and in well-consolidated rocks at equivalent PGA levels.
Highlights
Central New Zealand has experienced several moment magnyeitaurds,eth(Me lwa)rg7esotroflawrgheircheawrethrequthaeke18r4u8ptMurwes7.i4n−7th.7e last 200 Awatere earthquake [1, 2], the 1855 Mw 8.1+ Wairarapa earthquake [3], and the 1888 Mw 7−7.3 Hope earthquake [4]
Earthquake-induced static and dynamic stresses (e.g., [21]) and local hydrogeological factors [22] influence groundwater level responses. In this first report on the Kaikōura earthquake’s hydrogeological effects, we document an extensive dataset of groundwater level responses in order to assess the level to which earthquakedriven and local hydrogeological factors contributed to the national scale groundwater level response
Some monitoring wells that experienced low levels of shaking showed a larger water level change than wells that experienced high levels of shaking, such as wells in Cromwell Gorge (Figure 7). This may be due to local hydrogeological conditions that partly contribute to the characteristics of water level changes
Summary
Central New Zealand has experienced several moment magnyeitaurds,eth(Me lwa)rg7esotroflawrgheircheawrethrequthaeke18r4u8ptMurwes7.i4n−7th.7e last 200 Awatere earthquake [1, 2], the 1855 Mw 8.1+ Wairarapa earthquake [3], and the 1888 Mw 7−7.3 Hope earthquake [4]. The Kaikōura earthquake initiated in the Waiau Plains in northern Canterbury, New Zealand, on an oblique thrust at a depth of ~15 km. It propagated upwards and northwards, forming a complex rupture along a ~180 km zone that involved at least 21 faults [12, 13], producing widespread shaking reaching maximum Modified Mercalli Intensity of IX. Earthquake-induced static and dynamic stresses (e.g., [21]) and local hydrogeological factors [22] influence groundwater level responses In this first report on the Kaikōura earthquake’s hydrogeological effects, we document an extensive dataset of groundwater level responses in order to assess the level to which earthquakedriven and local hydrogeological factors contributed to the national scale groundwater level response. In comparison to other case studies, the Kaikōura earthquake dataset is significant as it includes groundwater level responses collated from a variety of hydrogeological settings
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