When the earth blisters: Exploring recurrent liquefaction features in the coastal system of Christchurch, New Zealand

Abstract

The 14 February, or Valentine's Day, 2016 earthquake located offshore of Christchurch produced a new generation of liquefaction in the coastal environment of Christchurch, an environment of recurrent liquefaction during the 2010-2011 Canterbury Earthquake Sequence. The Valentine's Day earthquake occurred while trenches were open at a site in the coastal environment for studying the 2010-2011 liquefaction features. Observations in the 2016 trenches provided insights into the formation of a suite of surface and subsurface liquefaction features characteristic of the dune deposits, related to the persistent shallow water table, well-sorted sands within the liquefiable layer and the soil above. Given these conducive conditions, there is a high potential that all earthquakes capable of inducing liquefaction may have been recorded during formation of the dunes near Christchurch. However, overprinting by subsequent generations of liquefaction features may be common and present challenges in unravelling the event history.

Micromorphological analysis of liquefaction features in alluvial and coastal environments of Christchurch, New Zealand

“…In contrast, the coastal dune soils are characterized by well to moderately sorted fine and medium sandy sediment (Giona Bucci et al ., ) and by an intergrain–microaggregate or close packing microstructure, locally single grain (no fine material bounding the grains) or bridged (presence of fine material bridging the grains; Fig. ).…”

“…Studies following 14 February 2016 (after the QEII trenching campaign) showed that the ‘L2 unit’ observed at QEII park is a type of liquefaction feature, namely sand sills that split A‐horizons in the coastal dune setting (Giona Bucci et al ., ). While the A‐horizon splitting in QEII had a small dyke associated with it, other similar features may not have them (as a liquefiable source layer can be immediately below the A‐horizon).…”

Probabilistic seismic source location and magnitude via inverse analysis of paleoliquefaction evidence

“…The reader is referred to the overviews of field interpretation by Obermeier et al (2001, 2005), and to the studies of Sims (1973), Obermeier and Dickenson (2000), Cox et al (2007), Tuttle et al (2002, 2005, 2019b), Tuttle and Atkinson (2010), Giona Bucci et al (2018a, 2018b), and Villamor et al (2016) for specific case studies. In addition, Sims and Garvin (1995), Quigley et al (2013), Bastin et al (2016), Giona Bucci et al (2017), Tuttle et al (2017), and Maurer et al (2019) discuss field interpretation specific to spatiotemporally clustered earthquakes. Once identified, paleoliquefaction features may be dated via radiocarbon, optically stimulated luminescence, archeological context, stratigraphic context, or soil development indicators, such as weathering and biologic activity, among others.…”