Back in 2006, IT’S OUR FAULT supported Wellington to become a more resilient city through a comprehensive study of the likelihood of large Wellington earthquakes, their effects and impacts on humans and the built environment.
Today, the programme is supporting the region's growing resilience with targeted science and policy research projects in line with community and local government needs.
This task addresses the current needs of Wellington’s Territorial Authorities (TA) requirements the National Policy Statement on Urban Development 2022, specifically using natural hazards as “qualifying matters” as exceptions to the intensification requirements. The pace of adoption has meant each TA has developed its own criteria, weighting and balance of planning decisions int heir draft district plans and this task will review the various proposals in the draft district plans to document the criteria, decisions, and factors to help inform a common framework for the region and consistency of approach. This work will inform the Wellington Regional Growth framework, and those councils in the region who have not yet sought to apply the NPS-UD within their district plans.
A core part of the Planning and Policy project, and its predecessors, are the Science to Practice Workshops. Earlier workshops run at GNS Science sought to capture all natural hazards, relevant planning practice and Councils across the Wellington Region, but more recently workshops have been held with individual TA’s. This establishes a relationship and understanding of the natural hazard planning challenges they face and results in a workshop tailored to assist in addressing these challenges. This year the workshop will be for Wellington City Council.
The surface of Aotearoa is always on the move. Whether the result of tectonic (earthquakes, Slow Slip Events, Interseismic) and volcanic processes or more localised ground deformation caused by, for example, landslides, compaction/settlement, stream erosion and anthropogenic processes. Traditional ground-based methods to detect and monitor ground movements over large urban areas are costly and provide limited spatial and temporal resolutions. InSAR provides an alternative method which can provide deformation data at building scale spatial resolutions with fortnightly updates.
This project will exploit high-resolution (3 x 14 m) InSARdata covering the Wellington region following the 2016 Kaikōura earthquake toidentify anomalous areas of ground movement, quantify the rate and temporalevolution, and classify the likely processes causing the movement. We willproduce a geospatial ‘anomaly’ map identifying ground deformation areasclassified based on the dominant process(s) causing the deformation. Such hotspotscan then be overlain on infrastructure maps to identify potential hazardousground deformation and allow hazards to be identified, monitored and if needed,mitigated.
In the past few years, It’s Our Fault tsunami tasks have focused on tsunami hazard identification, tsunami arrival time estimates and evacuation modelling. In this year, we undertake the final agent-based evacuation modelling for Kāpiti Coast suburbs and start to investigate tsunami impacts on natural and man-made environments in the Greater Wellington Region. The research will be mainly focused on following aspects:
Agent-based evacuation modelling for Peka Peka, Te Horo Beach and Ōtaki Beach. Agent-based evacuation modelling simulates the movement of individual people during an evacuation, taking into account walking speeds, decisions speeds, and interactions between people(congestion). It is particularly useful to identify bottlenecks which can inform future response and urban planning.
Tsunami impact on coastal habitats(e.g., endangered little blue penguin or banded dotterel), and current coastal vegetation restoration efforts (e.g., those managed by DOC, council, associations, etc.) in major tsunami events; and
Tsunami impact on man-made environments, such as tsunami-induced currents and wave amplifications (seiche-related phenomena) in marinas. The focus of this study is on Mana Marina in Porirua, which experienced strong tsunami currents in recent (15 January 2022) Tonga tsunami.
The southern Hikurangi Subduction Zone is one of the biggest sources of seismic and tsunami hazard for the Wellington Region. Recent It’s Our Fault research has identified four earthquakes during the past 2000 years. These earthquake ages represent a major constraint for hazard models, but overall the subduction zone is still poorly understood. The work this year focuses on extending the earthquake record back in time and modelling earthquake shaking on the subduction zone and faults in the overlying plate (upper-plate faults).
Cores at Mataora-Wairau Lagoon have been used to constrain the timing of two subduction earthquakes, at ~500 and ~800 years BP. Evidence for older earthquakes will be examined from vibra cores collected from the top 5–7 m of sediment in the lagoon. If evidence of older earthquakes is found, the likely subsidence will be defined using paleo-ecological techniques. Bayesian age modelling of radiocarbon ages from the sediments will be used to further constrain the timing of past earthquakes, allowing comparisons with other earthquake ages from across the Wellington Region and northern South Island. Dislocation and tsunami modelling will be used to constrain likely characteristics of earthquakes that cause deformation at multiple sites.
In the Cook Strait area, it is often uncertain whether observed subsidence and especially uplift is due to: (1) a past subduction earthquake; or (2) rupture of a fault within the overriding Australian Plate. One of the best evidence to distinguish these may be distribution of landslides onshore and the earthquake-triggered turbidites in lakes and offshore canyons. We will run models of earthquake ground shaking (motions) to test whether landslides and turbidites are likely to be useful for distinguishing between subduction and upper-plate earthquakes in the Wellington Region. We will conduct scenario-based modelling that will encompass a range of fault geometries and include combined ruptures of the subduction interface with upper-plate faults. The modelling will complement probabilistic estimates of ground shaking from the ongoing 2022 National Seismic Hazard Model revision.
Several new likely active faults have recently been identified near towns in the Wairarapa Valley. These were identified from their expression in the landscape using Light Detecting and Ranging (LiDAR) data. Little is known about these faults and because of this, and their locations, they warrant further study to: (1) confirm whether they are active faults; and (2) if they are faults, what paleoseismic investigations could be undertaken to determine their recurrence interval and slip rate. We will address this through the use of non-invasive Ground Penetrating Radar (GPR). GPR uses radar pulses to image the shallow subsurface providing a window which we can use to search for offset stratigraphy and interrogate these newly identified faults. Transects will be run across selected mapped faults and compared with transects across non-fault features in similar materials. Reconnaissance fieldwork will also be undertaken to investigate the ages of terraces cut by faults and identifying suitable sites for further paleoseismic investigations if warranted.