Recurrent liquefaction in Christchurch, New Zealand, during the Canterbury earthquake sequence

Continuous observational monitoring of a study site in eastern Christchurch, New Zealand, following the 2010 M-w 7.1 Darfield earthquake has recorded ten distinct liquefaction episodes in the mainshock-aftershock sequence. Three nearby accelerometers allow calibration between the geological expressions of liquefaction and the intensity of earthquake-induced surface ground motion at the site. Sand blow formation was generated by M-w 5.2-7.1 earthquakes with M-w 7.5-normalized peak ground accelerations (PGA(7.5)) of >= 0.057 g (acceleration due to gravity). Silt drapes between successive sand blow deposits provide markers for delineating distinct liquefaction-inducing earthquakes in the geologic record. However, erosion quickly modifies the surface of sand blows into alluvial and aeolian forms that complicate geologic diagnosis. The two feeder-dike generations identified in subsurface investigations significantly underrepresent the number of liquefaction-inducing earthquakes due to extensive dike reactivation. New constitutive equations enable PGA(7.5) variations to be estimated from the thickness and areal extent of sand blows.