During the 2010 - 2011 Canterbury earthquake sequence, extensive liquefaction was observed in many areas of Christchurch city and its surroundings, causing widespread damage to buildings and infrastructure. While existing simplified methods were found to work well in some areas of the city, there were also large areas where these methods did not perform satisfactorily. In some of these cases, researchers have proposed that layers of fine grained material within the soil profile may be responsible for preventing the manifestation of liquefaction. This paper presents preliminary findings on the mechanisms at play when pressure differentials exist across a clay layer. It is found that if the clay layer is unable to distort, then pore fluid is unable to break-through the layer even with relatively high pressures, resulting in dissipation of excess pore pressures by seepage. If the layers are however able to distort, then it is possible for the pore fluid to break through the clay layer, potentially resulting in adverse effects in terms of the severity of liquefaction.
This paper provides a photographic tour of the ground-surface rupture features of the Greendale Fault, formed during the 4th September 2010 Darfield Earthquake. The fault, previously unknown, produced at least 29.5 km of strike-slip surface deformation of right-lateral (dextral) sense. Deformation, spread over a zone between 30 and 300 m wide, consisted mostly of horizontal flexure with subsidiary discrete shears, the latter only prominent where overall displacement across the zone exceeded about 1.5 m. A remarkable feature of this event was its location in an intensively farmed landscape, where a multitude of straight markers, such as fences, roads and ditches, allowed precise measurements of offsets, and permitted well-defined limits to be placed on the length and widths of the surface rupture deformation.
The structure and geomorphology of active orogens evolves on time scales ranging from a single earthquake to millions of years of tectonic deformation. Analysis of crustal deformation using new and established remote sensing techniques, and integration of these data with field mapping, geochronology and the sedimentary record, create new opportunities to understand orogenic evolution over these timescales. Timor Leste (East Timor) lies on the northern collisional boundary between continental crust from the Australian Plate and the Banda volcanic arc. GPS studies have indicated that the island of Timor is actively shortening. Field mapping and fault kinematic analysis of an emergent Pliocene marine sequence identifies gentle folding, overprinted by a predominance of NW-SE oriented dextral-normal faults and NE-SW oriented sinistral-normal faults that collectively bound large (5-20km2) bedrock massifs throughout the island. These fault systems intersect at non-Andersonian conjugate angles of approximately 120° and accommodate an estimated 20 km of orogen-parallel extension. Folding of Pliocene rocks in Timor may represent an early episode of contraction but the overall pattern of deformation is one of lateral crustal extrusion sub-parallel to the Banda Arc. Stratigraphic relationships suggest that extrusion began prior to 5.5 Ma, during and after initial uplift of the orogen. Sedimentological, geochemical and Nd isotope data indicate that the island of Timor was emergent and shedding terrigenous sediment into carbonate basins prior to 4.5 Ma. Synorogenic tectonic and sedimentary phases initiated almost synchronously across much of Timor Leste and <2 Myr before similar events in West Timor. An increase in plate coupling along this obliquely converging boundary, due to subduction of an outlying continental plateau at the Banda Trench, is proposed as a mechanism for uplift that accounts for orogen-parallel extension and early uplift of Timor Leste. Rapid bathymetric changes around Timor are likely to have played an important role in evolution of the Indonesian Seaway. The 2010 Mw 7.1 Darfield (Canterbury) earthquake in New Zealand was complex, involving multiple faults with strike-slip, reverse and normal displacements. Multi-temporal cadastral surveying and airborne light detection and ranging (LiDAR) surveys allowed surface deformation at the junction of three faults to be analyzed in this study in unprecedented detail. A nested, localized restraining stepover with contractional bulging was identified in an area with the overall fault structure of a releasing bend, highlighting the surface complexities that may develop in fault interaction zones during a single earthquake sequence. The earthquake also caused river avulsion and flooding in this area. Geomorphic investigations of these rivers prior to the earthquake identify plausible precursory patterns, including channel migration and narrowing. Comparison of the pre and post-earthquake geomorphology of the fault rupture also suggests that a subtle scarp or groove was present along much of the trace prior to the Darfield earthquake. Hydrogeology and well logs support a hypothesis of extended slip history and suggests that that the Selwyn River fan may be infilling a graben that has accumulated late Quaternary vertical slip of <30 m. Investigating fault behavior, geomorphic and sedimentary responses over a multitude of time-scales and at different study sites provides insights into fault interactions and orogenesis during single earthquakes and over millions of years of plate boundary deformation.
From small coastal settlements to large cities, communities are exposed to both the direct and indirect consequences of climate-change induced sea-level rise (SLR). Above the ground surface, short- and long-term coastal effects of SLR are visible and cause damage from flooding, erosion, and loss of habitats and ecosystems. Below the ground surface, the effects are less visible but nonetheless extensive. Groundwater is present at shallow depth in the coastal zone and the effects of SLR on shallow groundwater threaten water security, agricultural production and infrastructure. Groundwater flooding, a hydrological hazard results from the process of water table rise, where the groundwater surface intersects or goes above the land surface due to changing conditions. The coastal zone is a complex dynamic space between saltwater and freshwater environments above and below the ground surface, and coastal groundwater hazards are intensified due to SLR. However, current monitoring of coastal shallow groundwater levels and salinity does not occur sufficiently to mitigate and adapt to the groundwater hazard. This thesis provides insights into the dynamics of coastal shallow groundwater, urban monitoring networks, simulations of water table rise and the issues posed by shallow groundwater changes driven by SLR and effects on flooding. The first study reviewed processes of coastal groundwater rise and simulation tools used to evaluate possible impacts of SLR. The benefits and limitations of the two main methods to assess coastal groundwater rise and its contribution to flooding - spatial interpolation and numerical tools - were discussed. The review highlighted the need for methodology comparisons between spatial interpolation and numerical tools to guide future work. The simulation tools that are used to evaluate changes in urban hydrogeology due to SLR do not specifically estimate groundwater flooding. Current monitoring practices do not capture evidence for groundwater rise with SLR. Therefore, the assessment methods need to rely on improved coastal groundwater monitoring networks focused on water quality, saltwater intrusion, and continuous groundwater levels records near the coastline, tidally influenced surface water bodies, and critical infrastructure. The second study focused on an urban shallow groundwater monitoring network and assessed its development, current physical condition and usefulness for SLR research. Following the 2010-2011 Canterbury Earthquake Sequence, in Otautahi Christchurch, ¯ Aotearoa New Zealand, shallow groundwater data acquisition and establishment of a geotechnical database provided unprecedented information on subsurface conditions. The monitoring infrastructure provided high spatio-temporal resolution records of shallow groundwater levels, which opened the field of New Zealand-based urban groundwater studies. Field surveys and digital information reviews showed that the monitoring net work was in overall good condition and robust, despite some maintenance issues. The dataset held by the city and regional councils should be more widely used to benefit the community, urban water management, researchers and practitioners, facing decisions to adapt and protect coastal areas from the impacts of climate change and SLR. The third study determined characteristics of shallow groundwater, including spatial and temporal trends in depths to groundwater and their relationship to natural and an thropogenic stressors. The study used depth to groundwater measurements from the uniquely extensive and densely spaced monitoring network in Otautahi Christchurch, ¯ Aotearoa New Zealand. Data-driven analysis approaches were applied, including spa tial interpolation, autocorrelation, clustering, cross-correlation, and trend analysis. This comprehensive approach revealed discernible clusters and trends within the dataset, pro viding valuable insights into the spatial and temporal variability of shallow groundwater in urban coastal settings. Responses to stresses such as rainfall events and stream flow were successfully classified using clustering analysis, while anthropogenic influences were more challenging. The primary feature in hydrograph classification proved to be the prox imity to tidal rivers and their correlation with tidal signals. This study highlighted the importance of monitoring coastal groundwater and the need for a better understanding of its effects on urban infrastructure and the built environment. The fourth study focused on simulating the effects of SLR on water table rise. These processes may lead to groundwater flooding and infrastructure challenges. A numerical model was used to assess the transient water table movement in response to SLR. Various SLR scenarios and rates were used to simulate the magnitudes and rates of water table rise, considering a range of aquifer parameters for both fixed-head and fixed-flux inland boundary conditions. The magnitudes and rates of water table rise were always less than but proportional to SLR and decreased with distance from the coastline. The magnitude and rate of water table rise in response to SLR were the largest for fixed flux inland boundary conditions, but it takes a long time for conditions to equilibrate. Fixed-flux conditions were found to pose a greater hazard as the maximum impact may not be experienced for decades, posing challenges to planners and managers of coastal groundwater systems. Adding a drain reduced the magnitude and rate of water table rise, more on the inland side than on the coastal side. The final study examined the key impacts of SLR on coastal shallow groundwater, and subsequent challenges faced by infrastructure asset managers. The study showed that current and future issues such as saltwater intrusion, flooding, and earthquake liquefaction hazard due to groundwater are exacerbated by climate change-driven SLR. A key issue is determining who will take responsibility for shallow groundwater management in areas with multiple and overlapping local government jurisdictions. Another key finding is that current techniques to manage groundwater in infrastructure construction/operation and land management will be applied in future, and challenges to coastal infrastructure adaptation will be posed by political and economic considerations rather than technical understanding.
