Geotechnical aspects of the 22 February 2011 Christchurch earthquake

Abstract

The 22 February 2011, Mw6.2-6.3 Christchurch earthquake is the most costly earthquake to affect New Zealand, causing 181 fatalities and severely damaging thousands of residential and commercial buildings, and most of the city lifelines and infrastructure. This manuscript presents an overview of observed geotechnical aspects of this earthquake as well as some of the completed and on-going research investigations. A unique aspect, which is particularly emphasized, is the severity and spatial extent of liquefaction occurring in native soils. Overall, both the spatial extent and severity of liquefaction in the city was greater than in the preceding 4th September 2010 Darfield earthquake, including numerous areas that liquefied in both events. Liquefaction and lateral spreading, variable over both large and short spatial scales, affected commercial structures in the Central Business District (CBD) in a variety of ways including: total and differential settlements and tilting; punching settlements of structures with shallow foundations; differential movements of components of complex structures; and interaction of adjacent structures via common foundation soils. Liquefaction was most severe in residential areas located to the east of the CBD as a result of stronger ground shaking due to the proximity to the causative fault, a high water table approximately 1m from the surface, and soils with composition and states of high susceptibility and potential for liquefaction. Total and differential settlements, and lateral movements, due to liquefaction and lateral spreading is estimated to have severely compromised 15,000 residential structures, the majority of which otherwise sustained only minor to moderate damage directly due to inertial loading from ground shaking. Liquefaction also had a profound effect on lifelines and other infrastructure, particularly bridge structures, and underground services. Minor damage was also observed at flood stop banks to the north of the city, which were more severely impacted in the 4th September 2010 Darfield earthquake. Due to the large high-frequency ground motion in the Port hills numerous rock falls and landslides also occurred, resulting in several fatalities and rendering some residential areas uninhabitable.

The impact of the Canterbury earthquakes on successful school leaving for adolescents

“…Four general electorates (Christchurch Central, Christchurch East, Port Hills, and Waimakariri) had catchments in zones that were seriously damaged, whereas three general electorates (Ilam, Selwyn, and Wigram) were situated in less‐affected zones (designated high‐ and low‐impact zones respectively) (see http://www.elections.org.nz/events/electorate-boundary-review/final-electorate-boundaries for details). These designations are based on local knowledge, but are supported by mapping of the earthquakes’ locations 26 and damage from rockfall and liquefaction, 27,28 all of which cluster in the high‐impact zone areas. Data was extracted to examine trends for high‐impact zones compared with low‐impact zones and with national trends.…”

Geotechnical aspects of the 2016 Kaikōura earthquake on the South Island of New Zealand

“…Severe manifestations of liquefaction were recorded in the area of the Equestrian Park and the Blenheim Rowing Club however, very few buildings are present in these areas, and the engineering impact was generally low. It is also important to note that despite the very loose nature of these deposits, the extent and quantity of ejecta is significantly less than what was observed in either of the 2010 Darfield or 2011 Christchurch Earthquakes [16,17]. Some moderate liquefaction was observed in a few locations within the township of Blenheim, but these locations were either along the river or in the area of the sports fields at the north of the town and had limited impact on infrastructure.…”

Paleoliquefaction Studies and the Evaluation of Seismic Hazard

“…However, there are examples of modern earthquakes that produced liquefaction fields not fitting these general patterns. For example, the 2010 M 7.1 Darfield (New Zealand) earthquake, produced a liquefaction field skewed toward the coast due to regional differences in liquefaction susceptibility of sediment and water table depth [30,[184][185][186][187][188][189][190]. The 2002 M 7.9 Denali fault (Alaska) earthquake produced an extensive liquefaction field (at least 100 km from the epicenter) [94] that increased in severity from west to east, or from the main shock to the third subevent [93,94].…”