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

Abstract

a b s t r a c tSeismic 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 wellinstrumented, 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 (M w ) 7.1 Darfield earthquake and M w 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) ≥0.1-0.3 g), and the maximum distances between earthquake rupture and environmental response (R rup ), both generally increased with increased earthquake M w , 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 M w . In most cases, the most severe liquefaction, rockfall, cliff collapse, subsidence, flooding, tree damage, and biologic habitat changes were triggered by proximal, moderate magnitude (M w ≤ 6.2) earthquakes on blind faults. CES environmental effects will be incompletely preserved in the geologic record and variably diagnostic of spatial and temporal earthquake clustering. Liquefaction feeder dikes in areas of severe and recurrent liquefaction will provide the best preserved and potentially most diagnostic CES features. Rockfall talus deposits and boulders will be well preserved and potentially diagnostic of the strong intensity of CES shaking, but challenging to decipher in terms of single versus multiple events. Most other phenomena will be transient (e.g., distal groundwater r...

The environmental effects of the 1743 Salento earthquake (Apulia, southern Italy): a contribution to seismic hazard assessment of the Salento Peninsula

“…The main advantage of the ESI-07 scale is the classification, quantification and measurement of several known geological, hydrological, geomorphologic and botanical features that are associated with each intensity degree. This scale has been tested worldwide, in the case of several modern, historical earthquakes and paleoearthquakes (Silva et al 2008;Reicherter et al 2009;Lekkas 2010;Papanikolaou 2011;Giles 2013;Porfido et al 2015a, b;Serva et al 2015;Heddar et al 2016;Quigley et al 2016;Sanchez and Maldonado 2016).…”

Response to Brendan Duffy's comments

“…Which of them could have been targeted with this technique, and over what timescale. Maybe put together a useful chart/table showing the preservation potential, accuracy, precision, ease of deployment, best vertical resolution (critical if you want to document uplifts of half a meter or less), speed of survey, skill requirements, etc of the various techniques and illustrating why this one is important -I am thinking something like Table 2B in Quigley et al (2016), in which the lead author was responsible for another biological assessment of vertical displacement. Or maybe a McCalpin style graphic.…”

Paleoliquefaction Studies and the Evaluation of Seismic Hazard

“…Harp et al [94] attributed this unusual distribution of liquefaction to differences in fault length, duration of shaking, and lower frequency content of the third subevent. Therefore, factors that can influence the size and distribution of liquefaction features, such as regional tectonics and earthquake characteristics (e.g., style of faulting, directivity of seismic energy, and attenuation and amplification of ground motion), as well as local site conditions (e.g., grain-size distribution and relative density of sediment, distribution of liquefiable sediment, and water table depth), should be considered when making interpretations about paleoearthquakes from paleoliquefaction features (e.g., References [30,51,56,75,95,100,147]). In the case of seismically triggered soft-sediment deformation structures in lacustrine deposits, the spatial distribution of the features and the intensity of deformation are used to construct isoclines of deformation and to identify the probable paleoearthquake source area [24].…”