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Articles, Christchurch uncovered

Over the last few weeks, we’ve been excavating a site in the CBD that’s yielded some of the most interesting artefacts we’ve see for a while. So, today on the blog, we’ve selected a few of these fascinating things for … Continue reading →

Images, eqnz.chch.2010

Photographs of the Brick Art unveiling, Greening the Rubble, on the former Asko site - corner of Victoria and Salisbury Streets, Christchurch 8 February 2011. From the collection of Christchurch City Libraries CCL-Brickart-2011-IMG_2484

Research papers, University of Canterbury Library

Bulk rock strength is greatly dependent on fracture density, so that reductions in rock strength associated with faulting and fracturing should be reflected by reduced shear coupling and hence S-wave velocity. This study is carried out along the Canterbury rangefront and in Otago. Both lie within the broader plate boundary deformation zone in the South Island of New Zealand. Therefore built structures are often, , located in areas where there are undetected or poorly defined faults with associated rock strength reduction. Where structures are sited near to, or across, such faults or fault-zones, they may sustain both shaking and ground deformation damage during an earthquake. Within this zone, management of seismic hazards needs to be based on accurate identification of the potential fault damage zone including the likely width of off-plane deformation. Lateral S-wave velocity variability provides one method of imaging and locating damage zones and off-plane deformation. This research demonstrates the utility of Multi-Channel Analysis of Surface Waves (MASW) to aid land-use planning in such fault-prone settings. Fundamentally, MASW uses surface wave dispersive characteristics to model a near surface profile of S-wave velocity variability as a proxy for bulk rock strength. The technique can aid fault-zone planning not only by locating and defining the extent of fault-zones, but also by defining within-zone variability that is readily correlated with measurable rock properties applicable to both foundation design and the distribution of surface deformation. The calibration sites presented here have well defined field relationships and known fault-zone exposure close to potential MASW survey sites. They were selected to represent a range of progressively softer lithologies from intact and fractured Torlesse Group basement hard rock (Dalethorpe) through softer Tertiary cover sediments (Boby’s Creek) and Quaternary gravels. This facilitated initial calibration of fracture intensity at a high-velocity-contrast site followed by exploration of the limits of shear zone resolution at lower velocity contrasts. Site models were constructed in AutoCAD in order to demonstrate spatial correlations between S-wave velocity and fault zone features. Site geology was incorporated in the models, along with geomorphology, river profiles, scanline locations and crosshole velocity measurement locations. Spatial data were recorded using a total-station survey. The interpreted MASW survey results are presented as two dimensional snapshot cross-sections of the three dimensional calibration-site models. These show strong correlations between MASW survey velocities and site geology, geomorphology, fluvial profiles and geotechnical parameters and observations. Correlations are particularly pronounced where high velocity contrasts exist, whilst weaker correlations are demonstrated in softer lithologies. Geomorphic correlations suggest that off-plane deformation can be imaged and interpreted in the presence of suitable topographic survey data. A promising new approach to in situ and laboratory soft-rock material and mass characterisation is also presented using a Ramset nail gun. Geotechnical investigations typically involve outcrop and laboratory scale determination of rock mass and material properties such as fracture density and unconfined compressive strength (UCS). This multi-scale approach is espoused by this study, with geotechnical and S-wave velocity data presented at multiple scales, from survey scale sonic velocity measurements, through outcrop scale scanline and crosshole sonic velocity measurements to laboratory scale property determination and sonic velocity measurements. S-wave velocities invariably increased with decreasing scale. These scaling relationships and strategies for dealing with them are investigated and presented. Finally, the MASW technique is applied to a concealed fault on the Taieri Ridge in Macraes Flat, Central Otago. Here, high velocity Otago Schist is faulted against low velocity sheared Tertiary and Quaternary sediments. This site highlights the structural sensitivity of the technique by apparently constraining the location of the principal fault, which had been ambiguous after standard processing of the seismic reflection data. Processing of the Taieri Ridge dataset has further led to the proposal of a novel surface wave imaging technique termed Swept Frequency Imaging (SFI). This inchoate technique apparently images the detailed structure of the fault-zone, and is in agreement with the conventionally-determined fault location and an existing partial trench. Overall, the results are promising and are expected to be supported by further trenching in the near future.

Images, Alexander Turnbull Library

Text at top left reads 'Don't forget rubbish day' The cartoon is a large wheelie bin stacked high with debris from 'old dunger buildings'. Someone in a damaged house nearby says 'Good riddance!' Context - Two earthquakes and hundreds of aftershocks have hit Christchurch, the first on 4 September 2010 and a second more devastating one on 22 February 2011. Earthquake Recovery Minister Gerry Brownlee may or may not have actually used the words 'old dungers' to describe some of Christchurch's heritage buildings that are not worth keeping but he might as well have done because many people believe that this is the way he thinks. Debate about which heritage buildings should be kept and which demolished has begun along with debate about how the city should be rebuilt. Quantity: 1 digital cartoon(s).

Images, UC QuakeStudies

Members of the public at Gap Filler's "Film in the Gap!" project. Behind the pair is a chalkboard sign outlining the project's programme for the evening of evening of April 10th, 2011 at Gap Filler's "Film in the Gap!" project. The sign reads, "Gap Filler: 1st - 10th of April. Free live music and films from 5pm onwards. 5pm: Plasticine Heroes, I gave These Guys 5 Bucks, 6pm: The Eastern, 7pm: Film - Candyman. Bring - cushion, chair, blanket, picnic. Coffee from 4:30pm daily. Ex demolition site. Please be safety aware. Proper footwear must be worn!". The sign is stuck to the rear wall of Mitre 10 in Beckenham, facing inwards to the site of the project.

Images, UC QuakeStudies

A photograph of the location of the Green Room garden on Colombo Street. White picket fences have been placed around the edges of the site and a platform has been constructed in the back-right corner. Two garden plots have been sectioned off using bricks to the right and front of the site. The front plot has been planted with shrubs and grass. A path leading between the gardens up to the platform has been filled with gravel. Wire fences have been placed around the entire section as a cordon.Crack'd for Christchurch comments, "The Green Room was built by Jonathan Hall and planted by Gina Payne."

Research papers, University of Canterbury Library

Results from a series of 1D seismic effective stress analyses of natural soil deposits from Christchurch are summarized. The analysed soil columns include sites whose performance during the 2010-2011 Canterbury earthquakes varied significantly, from no liquefaction manifestation at the ground surface to very severe liquefaction, in which case a large area of the site was covered by thick soil ejecta. Key soil profile characteristics and response mechanisms affecting the severity of surface liquefaction manifestation and subsequent damage are explored. The influence of shaking intensity on the triggering and contribution of these mechanisms is also discussed. Careful examination of the results highlights the importance of considering the deposit as a whole, i.e. a system of layers, including interactions between layers in the dynamic response and through pore water pressure redistribution and water flow.

Research papers, University of Canterbury Library

This paper summarizes the development of a region-wide surficial shear wave velocity model based on the combination of the large high-spatial-density database of cone penetration test (CPT) logs in and around Christchurch, New Zealand and a recently-developed Christchurch-specific empirical correlation between soil shear wave velocity and CPT. The ongoing development of this near-surface shear wave velocity model has applications for site characterization efforts via the development of maps of time-averaged shear wave velocities over specific depths, and the identification of regional similarities and differences in soil shear stiffness.

Research papers, University of Canterbury Library

This paper presents site-specific and spatially-distributed ground-motion intensity estimates which have been utilized in the aftermath of the 2010-2011 Canterbury, New Zealand earthquakes. The methodology underpinning the ground motion intensity estimation makes use of both prediction models for ground motion intensity and its within-event spatial correlation. A key benefit of the methodology is that the estimated ground motion intensity at a given location is not a single value but a distribution of values. The distribution is comprised of both a mean and standard deviation, with the standard deviation being a function of the distance to nearby observations at strong motion stations. The methodology is illustrated for two applications. Firstly, maps of conditional peak ground acceleration (PGA) have been developed for the major events in the Canterbury earthquake sequence, which among other things, have been utilized for assessing liquefaction triggering susceptibility of land in residential areas. Secondly, the conditional distribution of response spectral ordinates is obtained at the location of the Canterbury Television building (CTV), which catastrophically collapsed in the 22 February 2011 earthquake. The conditional response spectra provide insight for the selection of ground motion records for use in forensic seismic response analyses of important structures at locations where direct recordings are absent.

Other, National Library of New Zealand

Site where artists can donate songs which are compiled into an album to raise money for Christchurch earthquake relief. Includes information about the first album, how to submit a song, and an online shop; and news blog of quake- and album-related information.

Images, UC QuakeStudies

A photograph of the site of the Crowne Plaza Hotel taken from Radio New Zealand House on Durham Street. The hotel has been demolished, leaving large piles of rubble which an excavator is working to clear.

Images, UC QuakeStudies

Smoke billowing from the remains of the collapsed Canterbury Television building on Madras Street. Below, emergency personnel are searching through the rubble for trapped people. A piece of corrugated plastic is being used to slide pieces of debris off the site.