The Canterbury Earthquake Sequence (CES) of 2010-2011 caused widespread liquefaction in many parts of Christchurch. Observations from the CES highlight some sites were liquefaction was predicted by the simplified method but did not manifest. There are a number of reasons why the simplified method may over-predict liquefaction, one of these is the dynamic interaction between soil layers within a stratified deposit. Soil layer interaction occurs through two key mechanisms; modification of the ground motion due to seismic waves passing through deep liquefied layers, and the effect of pore water seepage from an area of high excess pore water pressure to the surrounding soil. In this way, soil layer interaction can significantly alter the liquefaction behaviour and surface manifestation of soils subject to seismic loading. This research aimed to develop an understanding of how soil layer interaction, in particular ground motion modification, affects the development of excess pore water pressures and liquefaction manifestation in a soil deposit subject to seismic loading. A 1-D soil column time history Effective Stress Analysis (ESA) was conducted to give an in depth assessment of the development of pore pressures in a number of soil deposits. For this analysis, ground motions, soil profiles and model parameters were required for the ESA. Deconvolution of ground motions recorded at the surface during the CES was used to develop some acceleration time histories to input at the base of the soil-column model. An analysis of 55 sites around Christchurch, where detailed site investigations have been carried out, was then conducted to identify some simplified soil profiles and soil characteristics. From this analysis, four soil profiles representative of different levels of liquefaction manifestation were developed. These were; two thick uniform and vertically continuous sandy deposits that were representative of sites were liquefaction manifested in both the Mw 7.1 September 2010 and the Mw 6.3 February 2011 earthquakes, and two vertically discontinuous profiles with interlayered liquefiable and non-liquefiable layers representative of sites that did not manifest liquefaction in either the September 2010 or the February 2011 events. Model parameters were then developed for these four representative soil profiles through calibration of the constitutive model in element test simulations. Simulations were run for each of the four profiles subject to three levels of loading intensity. The results were analysed for the effect of soil layer interaction. These were then compared to a simplified triggering analysis for the same four profiles to determine where the simplified method was accurate in predicting soil liquefaction (for the continuous sandy deposits) and were it was less accurate (the vertically discontinuous deposits where soil layer interaction was a factor).
Liquefaction affects late Holocene, loose packed and water saturated sediment subjected to cyclical shear stress. Liquefaction features in the geological record are important off-fault markers that inform about the occurrence of moderate to large earthquakes (> 5 Mw). The study of contemporary liquefaction features provides a better understanding of where to find past (paleo) liquefaction features, which, if identified and dated, can provide information on the occurrence, magnitude and timing of past earthquakes. This is particularly important in areas with blind active faults.
The extensive liquefaction caused by the 2010-2011 Canterbury Earthquake Sequence (CES) gave the geoscience community the opportunity to study the liquefaction process in different settings (alluvial, coastal and estuarine), investigating different aspects (e.g. geospatial correlation with landforms, thresholds for peak ground acceleration, resilience of infrastructures), and to collect a wealth geospatial dataset in the broad region of the Canterbury Plains.
The research presented in this dissertation examines the sedimentary architecture of two environments, the alluvial and coastal settings, affected by liquefaction during the CES. The novel aim of this study is to investigate how landform and subsurface sedimentary architecture influence liquefaction and its surface manifestation, to provide knowledge for locating studies of paleoliquefaction in future.
Two study cases documented in the alluvial setting showed that liquefaction features affected a crevasse splay and point bar ridges. However, the liquefaction source layer was linked to paleochannel floor deposits below the crevasse splay in the first case, and to the point bar deposits themselves in the second case.
This research documents liquefaction features in the coastal dune system of the Canterbury Plains in detail for the first time. In the coastal dune setting the liquefiable layer is near the surface. The pore water pressure is vented easily because the coastal dune soil profile is entirely composed of non-cohesive, very well sorted sandy sediment that weakly resists disturbance from fluidised sediment under pressure. As a consequence, the liquefied flow does not need to find a specific crack through which the sediment is vented at the surface; instead, the liquefied sand finds many closely spaced conduits to vent its excess of pore water pressure. Therefore, in the coastal dune setting it is rare to observe discrete dikes (as they are defined in the alluvial setting), instead A horizon delamination (splitting) and blistering (near surface sills) are more common. The differences in styles of surface venting lead to contrasts in patterns of ejecta in the two environments. Whereas the alluvial environment is characterised by coalesced sand blows forming lineations, the coastal dune environment hosts apparently randomly distributed isolated sand blows often associated with collapse features.
Amongst the techniques tested for the first time to investigate liquefaction features are: 3D GPR, which improved the accuracy of the trenching even six years after the liquefaction events; thin section analysis to investigate sediment fabric, which helped to discriminate liquefied sediment from its host sediment, and modern from paleoliquefaction features; a Random Forest classification based on the CES liquefaction map, which was used to test relationships between surface manifestation of liquefaction and topographic parameters. The results from this research will be used to target new study sites for future paleoliquefaction research and thus will improve the earthquake hazard assessment across New Zealand.
A review of the week's news including... a two billion dollar pay equity settlement, the Government announces changes it says are aimed at improving the quality of immigrants and controlling the quantity, irresponsible, unsafe, and unethical -- that's how a new Netflix series aimed at teenagers is being described, the top family court judge fires back at criticisms levelled at the court system by a new women's advocacy group, the Prime Minister who oversaw the dramatic undermining of unions now says unions have probably become too small, a review of Mental Health Services finds they are under pressure, under resourced and not widely understood, the Air Force's NH90 helicopters have been all but grounded, an eight-year-old girl is pulled alive from Manukau Harbour after treading water for more than two hours, the conversion of thousands of hectares of the Mackenzie Basin to dairy farms has been halted, tampons and sanitary pads will not be subsidised for all women by Pharmac, the government department set up to make the economy bigger isn't sure it can reach the goals it set for itself, Central Christchurch residents say they're under siege from sex workers and are threatening legal action, the massive Kaikoura earthquake may have saved the town from having to spend millions of dollars and the largest multi-sport event in the world has arrived in Auckland.
This article presents a quantitative case study on the site amplification effect observed at Heathcote Valley, New Zealand, during the 2010-2011 Canterbury earthquake sequence for 10 events that produced notable ground acceleration amplitudes up to 1.4g and 2.2g in the horizontal and vertical directions, respectively. We performed finite element analyses of the dynamic response of the valley, accounting for the realistic basin geometry and the soil non-linear response. The site-specific simulations performed significantly better than both empirical ground motion models and physics based regional-scale ground motion simulations (which empirically accounts for the site effects), reducing the spectral acceleration prediction bias by a factor of two in short vibration periods. However, our validation exercise demonstrated that it was necessary to quantify the level of uncertainty in the estimated bedrock motion using multiple recorded events, to understand how much the simplistic model can over- or under-estimate the ground motion intensities. Inferences from the analyses suggest that the Rayleigh waves generated near the basin edge contributed significantly to the observed high frequency (f>3Hz) amplification, in addition to the amplification caused by the strong soil-rock impedance contrast at the site fundamental frequency. Models with and without considering soil non-linear response illustrate, as expected, that the linear elastic assumption severely overestimates ground motions in high frequencies for strong earthquakes, especially when the contribution of basin edge-generated Rayleigh waves becomes significant. Our analyses also demonstrate that the effect of pressure-dependent soil velocities on the high frequency ground motions is as significant as the amplification caused by the basin edge-generated Rayleigh waves.
METIRIA TUREI to the Minister for the Environment: Ki Te Minita mō Te Taiao: Ka tukua e ngā paerewa e whakaarohia akehia nei mō te pai ake o te wai i roto i te pūhera Wai Mā, te kaha kē atu, te iti kē iho rānei o te uru atu o te tūkinotanga ki roto i ō tātou awa wai, e ngā mea whakakapi?
Translation: Do the proposed standards for water quality in the Clean Water package allow more pollution or less to enter our waterways than the ones they will replace?
BRETT HUDSON to the Minister of Finance: How much is the Government committing to spend on infrastructure over the next 4 years?
ANDREW LITTLE to the Prime Minister: Given his predecessor told the Pike River families, “I’m here to give you absolute reassurance we’re committed to getting the boys out, and nothing’s going to change that”, when, if ever, will he be announcing the re-entry of the drift?
STUART SMITH to the Minister of Transport: What announcements has he made recently regarding the Government’s commitment to reinstate key transport links following the Kaikōura earthquake?
JACINDA ARDERN to the Minister for Children: When was she first notified that the Ministry for Vulnerable Children Oranga Tamariki, or its predecessor CYF, were placing children and younger persons in a hotel or motel for short-term care without a supervisor, and what was her first action, if any?
MELISSA LEE to the Minister of Health: Can he confirm that 55,000 care and support workers will share in the $2 billion pay equity settlement announced on 18 April 2017?
GRANT ROBERTSON to the Minister of Finance: Does he agree with the Dominion Post editorial that his Government has “singularly failed to answer the pressures of Auckland”; if not, why does he think they would write this?
ANDREW BAYLY to the Minister for Building and Construction: How do the latest reports on the level of building activity in Auckland and nationwide for the month, quarter, and year compare with 2016?
Rt Hon WINSTON PETERS to the Prime Minister: Does he stand by all his statements; if so, how?
PHIL TWYFORD to the Minister of Transport: Why has the completion of the $2.4 billion Western Ring Route been delayed, and when can Aucklanders expect the new motorway to be open?
EUGENIE SAGE to the Minister of Conservation: Is it Government policy to increase the logging of native forests on West Coast conservation land?
Dr MEGAN WOODS to the Minister supporting Greater Christchurch Regeneration: Does she agree that the first homes in the East Frame will be completed 5 months ahead of schedule?
Questions to Members
CLARE CURRAN to the Chairperson of the Commerce Committee: Does she intend to call for further submissions on the petition of Dame Fiona Kidman before it is reported back to the House, in light of the recently released footage shot inside the drift of the Pike River mine?
