The 2010–2011 Canterbury Earthquake Sequence: Environmental effects, seismic triggering thresholds and geologic legacy

• Published in: Tectonophysics 2016-03, Vol.672-673, p.228-274
• Main Authors: Quigley, Mark C., Hughes, Matthew W., Bradley, Brendon A., van Ballegooy, Sjoerd, Reid, Catherine, Morgenroth, Justin, Horton, Travis, Duffy, Brendan, Pettinga, Jarg R.
• Format: Article
• Language: English
• Subjects: Blinds; Canterbury Earthquake Sequence (CES); Christchurch; Diagnostic systems; Earthquake design; Earthquake engineering; Earthquake environmental effects; Earthquakes; Environment effects; Liquefaction; Seismic hazard; Shaking
• ISSN: 0040-1951; 1879-3266
• DOI: 10.1016/j.tecto.2016.01.044

Seismic shaking and tectonic deformation during strong earthquakes can trigger widespread environmental effects. The severity and extent of a given effect relates to the characteristics of the causative earthquake and the intrinsic properties of the affected media. Documentation of earthquake environmental effects in well-instrumented, historical earthquakes can enable seismologic triggering thresholds to be estimated across a spectrum of geologic, topographic and hydrologic site conditions, and implemented into seismic hazard assessments, geotechnical engineering designs, palaeoseismic interpretations, and forecasts of the impacts of future earthquakes. The 2010–2011 Canterbury Earthquake Sequence (CES), including the moment magnitude (Mw) 7.1 Darfield earthquake and Mw 6.2, 6.0, 5.9, and 5.8 aftershocks, occurred on a suite of previously unidentified, primarily blind, active faults in the eastern South Island of New Zealand. The CES is one of Earth's best recorded historical earthquake sequences. The location of the CES proximal to and beneath a major urban centre enabled rapid and detailed collection of vast amounts of field, geospatial, geotechnical, hydrologic, biologic, and seismologic data, and allowed incremental and cumulative environmental responses to seismic forcing to be documented throughout a protracted earthquake sequence. The CES caused multiple instances of tectonic surface deformation (≥3 events), surface manifestations of liquefaction (≥11 events), lateral spreading (≥6 events), rockfall (≥6 events), cliff collapse (≥3 events), subsidence (≥4 events), and hydrological (10s of events) and biological shifts (≥3 events). The terrestrial area affected by strong shaking (e.g. peak ground acceleration (PGA) ≥0.1–0.3g), and the maximum distances between earthquake rupture and environmental response (Rrup), both generally increased with increased earthquake Mw, but were also influenced by earthquake location and source characteristics. However, the severity of a given environmental response at any given site related predominantly to ground shaking characteristics (PGA, peak ground velocities) and site conditions (water table depth, soil type, geomorphic and topographic setting) rather than earthquake Mw. In most cases, the most severe liquefaction, rockfall, cliff collapse, subsidence, flooding, tree damage, and biologic habitat changes were triggered by proximal, moderate magnitude (Mw≤6.2) earthquakes on blind faults. CES environmental effect